The nice folks at PolyScience generously loaned me a Sonicprep ultrasonic homogenizer for a few weeks of experimentation.  If the last sentence sounded like gibberish, it’s probably a good idea to read Jethro’s post on our experiments for a little background knowledge.  The Sonicprep is a device that emits powerful ultrasonic energy through the tip of a metal probe, into your food.  Fundamentally, high-amplitude ultrasound is really good at two things: making stable emulsions and smashing molecules together. The Sonicprep excels in both applications, but has a few nuances to overcome before I can justify the price for this gorgeous piece of technology.  Here I’ll describe some of the tests I preformed with the Sonicprep (many with Jethro’s assistance) and the conclusions we reached. 

Making Emulsions

The Sonicprep is really good at emulsifying liquids.  Like, scary good.  The first thing I did after unboxing the beast of a machine was to pour arbitrary amounts of oil and water into small glasses and give them a whirl in the Sonicprep.  Within seconds, the oil and water were mixed into a pale “milk”, and there was almost no trace of the source liquids remaining. 

The photo at the top shows a small amount of chili oil being mixed into water.  I only let the machine run for a few seconds at full power, which is why you can see the unincorporated oil on the right-hand side.  However, if I had continued sonicating, all of the oil would have become incorporated.  This isn’t necessarily an oil-to-water ratio I’d recommend; it was mostly to illustrate the process.

Unfortunately, all of my oil-based emulsions were plagued by a confounding problem: they tasted like metal and smelled like an electrical fire.  I’ve talked to several other folks who routinely use ultrasonic homogenizers and nobody else has ever encountered the problem.  Chris Young (Modernist Cuisine co-author) suggested that the intense ultrasonic energy may be setting off a chain reaction of free radical release within the oil, but unfortunately I don’t have the equipment necessary to test this theory.  It is possible that there was something specific about the machine I was using, or perhaps I was attempting to mix quantities that were just too small… the jury is still out on the cause, but this threw an unfortunate wrench in most emulsion tests. 

I did manage to create some very promising fat-based emulsions.  For example, I made the Serious Eats 36-hour Sous Vide Porchetta, which yielded quite a bit of delicious, liquid fat.  I sonicated the seasoned fat together with apple and pear cider with a touch of added xanthan gum and it turned into an exquisite gravy with the texture of thickened heavy cream.  It was stable over several days and had far more flavor than a comparable dairy-based gravy.  WIN!

I also created emulsions with duck fat and used the Sonicprep to emulsify a vegan gelato.  It performed wonderfully at those tasks.

The picture to the left shows the tip of the Sonicprep submerged in water with a sesame oil float.  The “cloud” emitted from the tip is the turbulent cavitation created by the high-energy ultrasound waves. 

Alcohol

Most of the buzz I’d heard about the Sonicprep was related to its ability to “instant age” spirits.  By sonicating alcohol with charred oak chips and other flavorful substances, allegedly one could turn cheap booze into good booze.  This promise was tempting, so we ran a few tests.  The net-net is that the Sonicprep does seem to improve the quality and “agedness” of spirits through this process. 

However, (and this is a big deal) the Sonicprep didn’t produce our favorite faux-aged booze.  We set up a double-blind experiment in which we infused whiskey with charred American oak barrel chips and orange peel (rind and pith) using three different infusion methods.  We controlled the proportion of wood and orange to whiskey and proceeded to infuse with a) the Sonicprep, b) the Smoking Gun, and c) a whipping siphon with nitrous oxide.   I labeled each sample with a letter, then Jethro re-labeled each sample with a symbol (shown above) – that way, neither of us knew which was which.  We tasted all three samples and wrote down our tasting notes privately.  At the end, we compared our notes and discovered that we reached the same conclusion.  The Smoking Gun sample was our least favorite – I attribute this to the fact that orange peel is not meant for burning.  I’ve done experiments with Smoking Gun-smoked drinks before, and I’m a fan.  The Sonicprep sample came in second – it had a light smokiness and a little burn on the throat.  The nitrogen-cavitated sample we infused in the whipping siphon took first place – medium smokiness and a smoother finish.  This was a huge shock to both of us. 

So, we got a little more creative.  I had a notion that, if people enjoy smoking cigars while drinking cognac, a cigar-infused cognac might be delicious.  Unfortunately, Jethro’s neighborhood bodega didn’t carry actual cigars, so he grabbed a peach flavored Swisher Sweets instead.  Ooookkkay, we’re up for anything.  In trial one, we unrolled the cigar and sonicated the tobacco in a small bottle of Courvoisier (I know, we’re super classy).  This produced a drink that was indistinguishable from the control.  So, in trial two, we charred the tobacco and sonicated it into the liquor.  This produced a drink with the color of old coffee and the flavor of an ashtray’s butthole.  To date, it was the worst thing I’ve ever tasted. 

We also tried “barrel aging” beer using the same approach as our liquor trials.  The good news is, yes, you can barrel age beer.  Even PBR!  As you can tell, I’m very selective about my alcohol.  Unfortunately, in the process of sonicating the beer, the Sonicprep effectively degassed it.  Had we kept CO2 cartriges on-hand, this would have been easy to remedy.  Unfortunately, we only had nitrous which doesn’t produce the same acidic flavors.  Was barrel aged PBR good?  I’m not sure, honestly.  Without blind-tasting it, carbonated, at the same temperature as a control, my personal bias creeps in and influences what I think I prefer.  But, I believe it has promise.

I also decided to make beer using the Sonicprep.  My thinking was this: traditionally, you dissolve the ingredients in a batch of beer by boiling them in water.  But, the heat of boiling likely changes the flavor of the beer.  If you could dissolve the ingredients and extract flavors without boiling, you’d have a fundamentally different beer.  Perhaps it would be the whitest white beer ever!  So, I poured a batch of Belgian-style ale ingredients and distilled water into a 5-gallon plastic bucket and started sonicating. 

Unfortunately, the effective range of the Sonicprep tip is only a few inches, so it didn’t circulate the beer ingredients as I hoped.  The malt extract sank to the bottom and the fuggle floated on the top.  Hmph. 

Rather than give up (like a sane person might), I divided the 5-gallon batch into 1-liter mini-batches and processed them one-by-one.  I added charred oak chips and sonicated the beer on full power for about 5 minutes per batch, then poured the batch through a strainer.  Once I had reached the end of 5 gallons (which felt like days later) I added the yeast and let it do its thing.  Again, without a control to compare to it’s hard to render an objective judgment, but it’s a good beer.  There’s a faint note of charred oak and the beer is light in color, but in no way “white” – the malt extract is quite dark and is responsible for most of the color in the beer.  In any event, I got 5 gallons of a very drinkable beer that was never boiled.  I’ll call that a WIN.

Coffee

I reasoned that if the Sonicprep could pull flavors from charred oak, it might do interesting things with ground coffee.  The photo above shows two shots of espresso – the one on the left was pulled from my Capresso C1000 at full strength; the one on the right was 21g of ground espresso beans sonicated in 200g of water at 76C for 30 seconds at 100% power.  Clearly, the two methods produced different results.  The Sonicprep espresso has the cloudiness of an emulsion, leading me to hypothesize that some of the oils from the beans were suspended in the water.  Strangely, both espressos had the same strength.  Due to the different extraction temperatures (the Capresso is closer to 86C), the two samples have unique flavor notes.  [I sound like a broken record, but] without a blind taste test, I can’t honestly tell you my preference.  However, this result was enough to convince me that the Sonicprep does have the potential for novel applications with coffee. 

In Conclusion…

I get really excited every time I hear about a new piece of culinary technology.  In this case, as with most of the other tools in my kitchen, the technology itself isn’t new, but it’s application for food and cooking is just being discovered.  Ultrasonic machines like the Sonicprep have been used in laboratory sciences as “cell disruptors” and marketed as jewelry cleaners to commercial jewelers.  However, they are just beginning to find their place in the kitchen.  I admit that I was a little disappointed by some of the limitations of the  Sonicprep – low volume processing, the fact that it heats liquids as it processes, my metallic oil issue -  but I’m still convinced that there are novel culinary applications for this technology just waiting to be discovered… somebody just has to think them up! 

I’m planning to conduct a series of blind taste tests to gather objective data on the Sonicprep results compared to other methods.  Playing with the device has also turned on several lightbulbs in my head about the way we approach infusion – I now look at my whipping siphon, vacuum chamber and pressure cooker in a different way than I did before.  But, when someone does figure out the truly revolutionary use for high-amplitude ultrasound in the kitchen, we’ll wonder how we ever lived without it. 

After much ogling, I finally took the plunge and purchased a VacMaster chamber vacuum sealer when I caught an irresistible deal for an older model on Craigslist.  I had known for a while that my FoodSaver was woefully inadequate at sealing wet foods for sous vide, but after witnessing how much of a workhorse the chamber sealer is at the Modernist Cuisine lab, I knew it was an essential missing piece of gear for my own kitchen.  These are the results of my first real experimentation with the chamber vacuum sealer: “quick pickling.”

A chamber sealer pulls a much stronger vacuum than a FoodSaver – so strong, in fact, that it will boil water at room temperature.  When you apply this ultra-strong vacuum pressure to plant foods, you can physically change their cell structure in a way that causes the foods to quickly absorb  liquids that surround them.  Modernist Cuisine explains the phenomenon best:

The cells of plant tissue contain pockets of air and water called vacuoles.  As the outside pressure decreases during vacuum sealing, these vacuoles act like balloons rising up through the atmosphere, and like balloons they eventually pop.  The popped vacuoles cannot reinflate[…] so they collapse under the weight of atmospheric pressure as soon as the sealing chamber is opened.[…]
Incidentally, this phenomenon also is the reason that infusing liquids into fruits or vegetables under vacuum compression works so well.  Once the vacuoles rupture, they quickly fill with any surrounding liquid.

So, I set out to exploit this phenomenon with a bunch of different plant foods.  Here are the results.

Tomatoes

The image at the top of this post shows the outcome of my tomato experiments.  On the left is a raw tomato, sliced 3mm thick.  In the middle is a tomato infused with olive oil.  On the right is a tomato infused with olive oil and balsamic vinegar.  Since the oil replaces much of the water in the tomato slice, you can safely top these tomatoes with salt without the salt melting, which is a neat trick.

The image just above shows a macro shot of the oil and balsamic tomato slice.  You can actually see the expanded vacuoles, which are now filled with oil.  As the pressure in the vacuum chamber dropped, the tomatoes boiled vigorously in the olive oil – they actually looked like they were being deep-fried, but at room temperature.  I think there’s more to explore here…

Cucumber

[Raw on the left, infused on the right].  These are classic pickles.  I infused 3mm cucumber slices in a brine of rice wine vinegar, sugar, salt, water, coriander seed, black peppercorn and fresh dill.  Because the cell walls are collapsed, these pickles don’t quite have the same “snap” as traditional pickles, but they were still excellent.  Having total control over the flavor of the brine and being able to make pickles in less than 60 seconds more than makes up for the difference in mouthfeel.

Quince

[Raw on the left, infused on the right].  Because the quince was so firm, I sliced it to 3/4mm on the mandoline.  I pickled the slices with Noble Tonic No. 4 and thyme.  Although they are quite acidic as a standalone snack, they’d make a fantastic garnish for something fatty, like a slab of pork belly or a chunk of tuna.  They’re also much more attractive when they turn translucent.

Jicama

[Raw on the left, infused middle and right].  Much to my surprise, the jicama didn’t compress much or turn translucent.  However, it did do a fantastic job taking on surrounding flavors.  My first test was Sriracha and light coconut milk.  This worked like a charm – the liquid was quite thick, but even after I rinsed the jicama, the flavors remained.  The second test was a brine of apple cider and fennel seed.  This has the potential to become a fantastic slaw.  Although I was happy with the flavors, I didn’t compare the results of the vacuum compression to simply soaking jicama in these liquids, so I can’t say for sure that vacuum did any magic here.

Turnip

[Raw on the left, infused on the right]. This was one of the most promising results – I infused 3/4mm sliced raw turnip with Nobile Tonic No. 1 Maple Syrup.  In fairness, I could lick that maple syrup off a cast iron griddle and still love it.  However, the sweetness of the syrup added a wonderful complexity to the bitter, spicy finish of raw turnip.  I could see these infused turnip sheets used as a wrapper for a filling, or perhaps deep fried into chips.

I’m very excited about the results of this first round of testing, and I look forward to more experimentation with the chamber sealer.

I’ve assembled a list of must-have cooking gear, kitchen toys, and foodie fetishes for 2011.  If you have a food geek in your life and you’re looking for gift inspiration, I’m here to help.  They say “‘tis better to give,” but ‘tis best to give to someone who’ll cook you dinner in return!

	Bob Kramer 10" Carbon Steel Chef’s Knife by Zwilling J.A. Henckels® Say hello to the “it knife” of 2011. Bob Kramer is the only Master Bladesmith in the world who specializes in culinary knifes, and his rare, hand-made blades sell for thousands of dollars.  (see my post on touring Bob Kramer’s workshop.)  Now, he’s produced a line of exceptional quality carbon steel cutlery that conforms to his exacting standards, but is affordable enough for the home chef.  $349.95 – Sur La Table $349.95 – Amazon.com
	Skillet Bacon Jam Seattle residents are already familiar with the spreadable jar of heaven known as “Bacon Jam”.  Produced by the same Skillet group that brought us the Skillet Street Food truck and the Skillet Diner,  the jam is a mixture of rendered bacon and spices that adds a succulent kick to sandwiches, burgers, omelets, Ritz crackers, or any other bacon-submissive food.  Makes a great stocking stuffer – just hope you can fit into your stockings after you’ve plowed through a jar. $15.95 – Amazon.com
	Rouxbe Cooking School In this day and age, anything that’s worth doing is worth doing online – learning to cook is no exception.  Rouxbe is the world’s leading online cooking school that teaches people of all levels to become better, more confident cooks.  Focused on techniques, not recipes, Rouxbe offers over 1,100 close-up instructional videos that capture the exact same curriculum found in professional cooking schools around the world. $23.00/month (other packages available) – Rouxbe.com
	SousVide Supreme Any serious food geek cooks sous vide.  And those who don’t?  Well, they’re waiting for you to buy them a sous vide machine… that is, if you’re not up for building one yourself.  By far, the easiest way to get started with sous vide cooking is the SousVide Supreme line of water ovens.  Their machines are available in multiple sizes and colors and they’re currently running some fantastic deals for the holidays, including a Modernist Cuisine gift set! $299 and up – SousVideSupreme.com
	VacMaster Chamber Vacuum Sealer Whether you’re cooking sous vide or tackling a whole slew of other modernist techniques, a vacuum sealer is an absolute necessity.  FoodSaver-style sealers work fine for dry foods, but for wet foods like meat and fish or liquids of any kind, you need a chamber sealer.  Unlike an edge sealer, which sucks all of the air out of the bag from one edge, the VacMaster removes the air from the entire chamber, then seals the bag.  When the vacuum is released, the pressure of the atmosphere compresses the bag against its contents for a fool-proof, air-free seal with no messy liquid sucked from the edge of the bag.  $799 – SousVideSupreme.com $824 – Amazon.com
	Excalibur 3500 Deluxe Series 5 Tray Food Dehydrator If you thought dehydrators were just for jerky and fruit snacks, you’re missing a whole world of possible applications for dried foods.  For example, why not whip up some Shrimp in Cocktail Leather for your next dinner party?  The Excalibur dehydrator is the brand trusted by chefs everywhere.  The rectangular drying trays provide 8 square feet of drying space, and the 85º – 145ºF thermostat let’s you dehydrate everything from soup to nuts (and yes, jerky too)! $189.95 – Amazon.com
	Presto 1755 16-Quart Aluminum Pressure Cooker/Canner For some reason, lots of folks think of pressure cookers as “your grandmother’s kitchen gadget”.  And, while it’s true that grannie may have reached for her pressure cooker as a way to save time in the kitchen, their usefulness extends well beyond expediency.  Pressure cookers are fantastic for extracting flavors, for example, when making stocks and sauces.  When coupled with a little baking soda, they’re also key to making the best vegetable soups I’ve ever tasted.  I’d recommend purchasing a pressure canner rather than just a pressure cooker.  The difference is the inclusion of a pressure gauge which allows you to can many foods that you couldn’t otherwise safely preserve. $71.99 – Amazon.com
	Noble Tonics: Handcrafted Matured Maple Syrups & Vinegars This is my new favorite breakfast condiment: Tahitian Vanilla Bean & Egyptian Chomomile Blossom Matured Maple Syrup.  Just speaking its name evokes images of meticulous artisans patiently watching over these syrups as they mature in charred American oak barrels. It is to maple syrup what Château d’Yquem is to wine.  The complete line includes two maple syrups, a sherry bourbon oak vinegar, an heirloom lemon matured white wine vinegar, and XO, a viscous, rich “finishing vinegar”.  $22.95 – $69.95 – MikuniWildHarvest.com Disclosure: I received a free sample of Noble Tonic products.
	Eleven Madison Park: The Cookbook Although this cookbook was only released a few weeks ago, it’s already one of the most talked-about cookbooks of the year.  And rightfully so – this book is so much more than a cookbook; it is a window into the soul of Eleven Madison Park.  Featuring breathtaking photography and over 125 sophisticated recipes, this will be one of the [very few] cookbooks I reference on a regular basis, both for inspiration and for technique.  $31.50 [hardcover] – Amazon.com
	Momofuku Milk Bar Imagine an incredible collection of desserts that all seem like they were designed by stoners with phenomenal pastry skills.  That would, more or less, be Monofuku Milk Bar.  Written by pastry chef Christina Tosi, the book includes an entire section on cereal milk ice creams.  Other notable dishes include the infamous “crack pie”, “compost cookie”, and “gutter sundae” (directions: Go to the hardware store.  Buy a gutter.  Invite your friends and family over.  Make a gutter sundae to celebrate).  Yet, somehow, the whole thing is irresistible! $20.18 – Amazon.com
	Lucky Peach This has been a great year for chef David Chang and his ever-expanding influence.  Case in point: Lucky Peach.  In an era when print publishing is dying a very public death, Chang had the chutzpah to start his own food journal.  Issue Two’s theme is "The Sweet Spot," and will feature Rene Redzepi on vintage vegetables, Tajikistani apricots with Adam Gollner, a visit to Callaway Golf and Louisville Slugger, time-sensitive fermentation, banana pie with Momofuku Milk Bar chef Christina Tosi, and much, much more. $9.50/issue – Amazon.com
	Top Pot Hand-Forged Doughnuts: Secrets and Recipes for the Home Baker Top Pot Doughnuts are a treasured part of Seattle’s edible landscape.  Let it be said that no other doughnut pairs as well with a nonfat, fair trade, soy, double, vanilla cappuccino.  Committed bakers, casual home cooks, and sweet-toothed fans will eat up these 50 tried-and-true recipes from classic Old-Fashioneds to the signature Pink Feather Boa and become experts themselves after learning the secrets of doughnut-making tools, terms, and techniques (no, you don t need a deep fryer). $10.98 – Amazon.com
	Modernist Cuisine: The Art and Science of Cooking If you’re searching for a food geek gift that will make all others pale in comparison, look no further.  For the price of a stand mixer and a handful of tasteful stocking stuffers, you can give the gift that will keep your food geek cooking for a lifetime.  I’ve already written quite a bit about Modernist Cuisine, but for the first time ever, you can wrap it in a bow and put it under the tree.  Nothing says “Merry Christmas” like a 40 lb. cookbook! $450.84 – Amazon.com
	iSi Professional Food & Cream Gourmet Whipper Thanks to Ferran Adria and others, the term “culinary foam” now means more than whipped cream.  If you’re interested in experimenting with foam-at-home, you’ll need to own a whipping siphon.  A now-essential part of both sweet and savory preparations, whipping siphons are also great for quick infusions and making carbonated snacks.  Unlike cheaper siphons, this model is designed to handle more viscous liquids commonly called for in modernist preparations. $138.99 – Amazon.com iSi N20 Cream Chargers, 24-Pack: $15.75 – Amazon.com
	Krups 203 Electric Coffee and Spice Grinder with Stainless-Steel blades Textural transformations are a hallmark of modernist cooking, and powders play in important role in achieving the correct mouthfeel and presentation of many dishes.  If you’ve ever attempted to turn a solid into a powder using a blender or food processor, you’ll understand why it’s important to have the right tool for the job.  This spice grinder is compact, inexpensive and incredibly efficient at making very fine powders in a matter of seconds. $19.00 – Amazon.com
	Canon EOS 5D Mark II with EF 24-105mm f/4 L IS USM Lens Modern food-enthusiasts (see how hard I tried not to use the word “foodie”?) never travel without a camera in-hand.  But, approaching your plate of foie gras and truffles with a cell phone camera is as gauche as wearing a sport coat and shorts just to spite the dress code.  If you or the food geek in your life are ready to get serious about food photography, there’s currently no better value than the iconic Canon 5D Mark II.  It shoots 21MP stills and broadcast-quality video, all for less than a bottle of Chateau Margaux.  $3,019.98 – Amazon.com
	Nikon 1 J1 10.1 MP HD Digital Camera System with 10-30mm VR 1 NIKKOR Lens So, you’ve realized that you want to improve your food photography, but you don’t want to lug a giant (and conspicuous) DSLR to every restaurant you visit.  Nikon’s “1” line is a brand new imaging system that’s designed to be highly portable and highly performant.  Featuring interchangeable lenses, a high-speed sensor for great low-light shooting, and the ability to snap stills while you’re shooting 1080p HD video, this is a great camera for the fooderazzi.  $599.00 – Amazon.com

Happy Holidays,

Scott

As you may know, one hallmark of the photography in Modernist Cuisine is their use of cutaway photos that show what’s happening inside your food – and cookware – as you cook.  Since I plan on (eventually) trying to recreate all of the recipes in the  book, I thought it might be prudent to recreate those cutaway shots, too.  Unlike the MC lab, however, I don’t have a waterjet. 

Enter the fantastic folks at Flow International Corporation.  They happened to catch my half-joking tweet asking if anyone had a waterjet I could borrow, and as it turns out, they do.  In fact, Flow manufactures waterjet machines and invited me to visit them at their headquarters in Kent, WA.  When I arrived, they led me – and my box of fully intact cookware – into their demonstration room, an enormous space punctuated by a handful of monstrous waterjets machines. 

Under normal circumstances, they’d load a 3D model of the object we were cutting and the cutting nozzle would follow an exact path through the object.  However, since I just wanted my pans cut “in twain” the operator switched  the machine into manual mode and piloted the cutting head across the surface of the pan like a Jedi.  The video below shows the cutting process. 

Water and abrasive grit forced at 87,000 psi through an opening the size of a human hair is powerful. And, it doesn’t discriminate – it’ll cut paper, tile, glass, stone, metals (including titanium) and just about anything else that gets in its path. As it turns out, water jets are also commonly used for cutting food products.  Since the water jet doesn’t generate much heat as it cuts, it’s perfect for portioning frozen meat and fish or slicing a sheet of nougat into individual candy bars.  Of course, now I totally want one of these machines for home.  Cutting the crust off a loaf of Wonderbread would never be the same again.

The image at the top shows one of my new half-skillets and depicts the problem with cooking a thick steak on a hot surface (see those gray bands of well-done?).  Now I can do my very own cutaway shots, just like the big boys

Huge thanks to the fantastic folks at Flow for helping me out!

This idea was inspired by a post I recently ran across on The Novice Chef that showed an egg cooked in a waffle iron.  I thought that as pretty clever, so I ripped it off.  However, I don’t have a waffle iron.  I only have a waffle cone iron, which is great for making (duh) waffle cones, tuile, and other thin, ridged treats.  I heated the iron to about 250F (checking the surface temp with my infrared thermometer), then unplugged it.  These irons get so hot that, at full temperature, they’ll quickly scorch the eggs and you’re left with a flaky mess.  I separated the yolk and white of one egg and cooked them individually.  You are free to cook the yolk however you like – poach it, put it in a hemisphere mold and cook it in a combi-oven, cook sous vide in a bag, fry it, etc. 

Now I’m going to make a logical leap to try to justify this playful experiment: with a waffled texture, the egg will hold more condiment on its surface.  Butter, syrup, hot sauce, ketchup,  pea butter, balsamic vinegar… they can all hang out in the shallow ponds created by the waffled surface.  But who am I kidding?  This was just fun.

Seal Test

The Ziploc vacuum bags work via a special flat, plastic valve built into one corner.  To seal foods, you zip the top of the bag closed, then place the hand pump over the valve and pump until all the air is removed.  This process only takes a few seconds, but achieves a similar compression strength to the FoodSaver (I attempted to measure the strength of the vacuum, but neither the FoodSaver nor the Ziploc registered a vacuum pressure high enough to register on my vacuum pressure gauge).  And, unlike the FoodSaver, there’s no heat sealing required.  If you’ve ever had the unpleasant experience of trying to get a FoodSaver to seal moist foods, you’ll know that heat sealing and liquids are nearly incompatible.  I can’t count the number times I’ve had to reseal a vacuum bag of meat because the heat seal failed.  The Ziploc bags don’t solve the liquids problem completely (for that, you want a chamber vacuum sealer) but it does seal just as well for wet foods as dry ones. 

To compare the seal and permeability of each bag, I placed a folded paper towel in a Ziploc vacuum bag and an equivalently sized FoodSaver bag.  I measured the mass of each paper towel before sealing, then placed both bags in a 60C water bath for 8 hours.  I dried the bags and measured the mass of the paper towels from each – if there were any increase in mass, I could attribute it to a leak in the bag’s seal, or water permeability of the bag itself.  For both the Ziploc and FoodSaver bags, there was no detectable increase in mass, implying that when sealed properly, both bags offer the same leak resistance. 

Price

Since pricing varies between retailer, I’m running the numbers based on Amazon’s prices.

Ziploc Vacuum System
Starter Kit (includes pump and 3 quart bags) – $4.20
1 Gallon Bags – $0.69/ea

FoodSaver Vacuum System
FoodSaver V3460 – $149.50
1 Gallon Bags – $0.71/ea

Other Considerations

Although the Ziploc bags are just slightly cheaper than their FoodSaver equivalents, the FoodSaver system offers continuous rolls of bag material which I find to be extremely convenient for sealing odd-size foods like a rack or ribs.  In addition, the FoodSaver offers accessories such as rigid vacuum canisters.  In my experience, these canisters are the best part of the FoodSaver system.  Whereas vacuum bags don’t create negative atmospheric pressure (since the atmosphere keeps pressing the bag against the food) the canisters allow you to actually create a vacuum environment.  This is highly useful for making vacuum-set foams, vacuum brining or vacuum infusing foods. 

Since the Ziploc bags don’t rely on a heat seal, the bag is not permanently altered when you use it.  That means that you could theoretically re-use your Ziploc bags over and over again.  Ziploc (wisely) recommends against reuse in general because the bags are difficult to clean and the risk of contamination between uses is significant.  However, if you’re using the bags to store dry goods like rice or grain, you can open the top, take what you need, then reseal.  If you were using a FoodSaver, the bag would get about three inches shorter every time you wanted to open and close it. 

Both FoodSaver and Ziploc bags are BPA-free and have been tested for to meet food safety standards.  The Ziploc bags are advertised as microwave-safe, but are not intended for use in boiling water.  After eight hours at 60C in the sous vide bath, the Ziploc bag showed no signs of deterioration.  That’s great news if you want to cook red meat.  However, I did not test higher temperature cooking conditions.  The Ziploc bags are not marketed for sous vide cooking, though ironically the words “sous vide” appear on the bag because they are printed in both French and English (“sous vide” is French for vacuum). 

Given my experience so far, I highly recommend the Ziploc system.  For the ability to vacuum seal foods for less than five dollars, there’s no reason not to give it a try.  In my opinion, this is a great step toward reducing the total cost of cooking sous vide at home and reducing the barriers to entry for people who aren’t obsessively geeky in the kitchen.  And, of course, if you’re still looking for a good way to heat your water bath, may I recommend another cheap solution?

[If you noticed that the picture at the top of this post looks just like the picture comparing sous vide bags from Modernist Cuisine, +10 points!  Instead of sealing colored water, though, I opted for a heartier payload.]

Have you ever wondered what happens when you subject shelf-stable emulsions from your local grocery store to 3,000 times the force of Earth’s gravity using a centrifuge?  Yeah, me too! 

I chose three different types of emulsions: mayonnaise, salad dressing, and canned soup.  [I also tested spaghetti sauce, but one of the test vials exploded mid-‘fuge, so the results were inconclusive].  For each emulsion, I centrifuged two popular brands to note their differences in separation after an hour at 3,000 RPMs (equivalent to 3,000 Gs in my centrifuge).  It is important to note that an emulsion that separates under these conditions does not indicate a better or worse product, simply a stronger or weaker emulsion.  The goal of this experiment was not to determine which brand you should buy.  The goal of this experiment was to spin a bunch of shit at extremely high G-forces and see what happened. 

The results:

1. Best Foods Real Mayonnaise – Mayonnaise, as it turns out, is a pretty strong emulsion.  This brand showed a slight separation visible at the bottom of the vial, but more or less held together.  If I spun it for longer, I wonder if I would have ended up with a layer of egg and a layer of oil…
2. Miracle Whip – This was the strongest emulsion I tested, showing no signs of separation whatsoever.  I personally can’t stand the stuff, but for those of you who are fans of this mayo alternative, rest assured that it is highly acceleration-resistant.
3. Kroger Zesty Italian Dressing – If you’ve ever made an oil and vinegar salad dressing at home, you know it’s naturally prone to separation.  This brand separated easily leaving perfectly clear oil at the top, vinegar in the middle and solids at the bottom.  +1 for “just like mom makes”, especially if your mom makes it from a bottle.
4. Kraft Free Zesty Italian Dressing – I chose this product because, on the shelf, the emulsion looked extremely stable – all of the solids were held in suspension, which was likely for marketing reasons.  Although all of the solids separated out, the liquid phase didn’t clarify at all.  It seems the people at Kraft have found a way to make oil, water and vinegar extremely fond of one another.
5. Kroger Chunky New England Style Clam Chowder – I expected that the chunky solids would wind up compressed at the bottom of the vial, but I was surprised to discover that the soupy part of the soup held intact.  I guess Chef Kroger (cough, cough) must have been very careful with his roux when he made this particular can of soup.
6. Campbell’s Select Harvest 98% Fat Free New England Clam Chowder – As you can see, there was some significant separation in this sample.  My guess is the light-colored top layer of thin, watery liquid has something to do with the low fat claims on the label – diluting soup with water would certainly be an easier way to make it “healthier”. 

As I said earlier, this experiment was more about messing around than testing a hypothesis.  Speaking of messing around, what substances would you like me to try spinning?  The centrifuge is still my newest toy, and like all toys, I’m eager to fill it with unusual liquids. 

Did you know that you can cure meat at home using nothing more than a wine refrigerator? 

This was my first attempt at meat curing, and I’d say it went fantastically well.  This project was inspired by Matt Wright and his insanely beautiful blog, WrightFood.  Matt has some serious curing experience under his belt, and offers detailed recipes and techniques for home curing.  For this project, I followed his recipe for Duck Prosciutto (recipe is towards the bottom of the post). 

The recipe calls for curing duck breasts in salt for 24 hours before hanging them up to cure at 55F with 60% relative humidity until they have lost 30% of their original mass. 

Although I’ve got big plans in my head for building a high-tech curing chamber (one day), I also remembered that I had an unused wine refrigerator sitting in the basement.  Nothing is sadder than an empty wine fridge, so I decided to repurpose it for a bold new mission.  The fridge has an adjustable temperature setting for champagne, whites, reds and long-term storage.  Luckily for me, one of those settings corresponds to 55F.  I didn’t bother measuring the humidity in the wine fridge, but I reasoned that it would have to maintain a reasonable humidity level to keep wine corks from drying out.  The fridge also has a small fan, which is great for circulating the air inside and a desirable condition for curing meat. 

I followed Matt’s directions, though I accidentally let the breasts sit for 48 hours in salt (instead of 24) before hanging.  I weighed the breasts and recorded their starting weight and the date on a piece of tape which I affixed to the door of the wine refrigerator.  I also skipped the step of wrapping the duck breasts in cheesecloth, which Matt said was OK.  I let the breasts hang  in the wine fridge and I checked on them every 5 days or so, inspecting them for signs of bacterial growth (bad) and giving them a squeeze test [with clean hands] to check for doneness.  After 25 days, they looked and felt about right, so I weighed them.  They had lost about 27% of their weight, which was all from moisture leaving the meat.  I called it “done” and carefully sliced off my first taste of home-cured meat.  It was fantastic, if a little on the salty side.  However, I’m really thrilled with the results of my first attempt and I can’t wait to start curing more and more meat! 

As it turns out, a wine refrigerator is reasonably ideal for this kind of curing.  Temperature settings range from 45-65F with relative humidity of 55-75%, which is just about the sweet spot for slowly dehydrating and aging meat.  Most models use a piezoelectric cooling element, which is quiet and barely sips electricity.  Plus, these days, they’re cheap: wine fridges range from under $100 for a no-frills model, to $150 for a model with decent capacity, and well on into the stratosphere from there.  Just remove all but the top rack and you’ve got space to hang tens of pounds of meat at once! 

I’m planning to investigate retrofitting my wine fridge with strips of ultraviolet LED lighting as a safeguard against possible mold or bacterial growth during the aging process.  I also bought a USB scale, which I’d like to add so I can monitor the weight loss of my meats remotely.  I’ll report back once the retrofit is complete, but in the meantime, I’m going to go enjoy a well-deserved charcuterie platter straight from my own home.

Further Reading: Check out Matt’s Home Cured Duck Prosciutto, and his other charcuterie recipes.  He’s also got a great step-by-step guide on building a proper curing chamber at home. 

As you might know, I’ve been working on sous vide machine designs for a little over a year now.  I’m happy to announce today that I’ve finally got a model ready for sale: the Easy-Vide Sous Vide Water Oven for Kids! 

I discovered that children are currently the biggest untapped market for kitchen technology, and in order to make sous vide cooking pervasive in the future, we need to educate the next generation of chefs and home cooks.  I created the Easy-Vide to be the simplest, easiest and most fun way to teach kids about sous vide.

Features:

• Screw in the light bulb (included), fill the basin with water, and pug in the power cord. 
• No pesky temperature settings to remember.  The water bath is heated by the light bulb – it’s that simple!
• Works for all types of foods including steak, chicken, fish, and even vegetables!
• Kids will love searing their favorite snacks with the included Mini Blowtorch

I’m still in negotiations with several retailers, so check back soon for pricing and availability.  The Easy-Vide promises to be the must-have toy for the aspiring cook in your family!

For just that reason, I’ve rounded up the best and geekiest kitchen gifts of 2010.  And, if you’re feeling extra generous, I also threw in a few “luxury items” sure to induce a Christmas morning nerdgasm.

Books

2010 was a great year for cookbooks.  In fact, all of the books below are new this year, with the exception of Modernist Cuisine, which is available for preorder but won’t ship until March.  At $475, it’s not exactly a stocking stuffer, but you can spread out the joy by wrapping each of the five volumes separately. 

• Modernist Cuisine: The Art and Science of Cooking by Nathan Myhrvold, Chris Young, and Maxime Bilet – $475
• Keys to Good Cooking: A Guide to Making the Best of Foods and Recipes by Harold McGee – $19.23
• Noma: Time and Place in Nordic Cuisine by René Redzepi – $32.97
• Sous Vide for the Home Cook by Douglas Baldwin – $25.95
• Cooking for Geeks: Real Science, Great Hacks, and Good Food by Jeff Potter – $20.71
• Modern Gastronomy: A to Z by Ferran Adria – $43.90

Modernist Cooking “Ingredients”

If the food geek on your Christmas list is dying to pull off the latest techniques, he’ll need some ingredients.  I’ve found the WillPowder brand to be a great value for the price.

• For spherification (you’ll need all three): Sodium Alginate – $27.69, Calcium Chloride- $15.08, and Sodium Citrate – $13.62
• For gels: AGAR AGAR – $52.35, Methylcellulose F50 – $28.64
• Thickeners: Ultratex 3 – $13.42, Ultratex 8 – $18.12
• For foams: Versawhip 600K – $36.08
• For powders: Tapioca Maltodextrin – $14.13

Essential Kitchen Gear

Who doesn’t like playing with new toys?  Over the last year, prices of induction cooktops have plummeted.  They are a great way to expand your stovetop capacity, and they’re extremely energy efficient for heating small quantities of food. 

• Max Burton 6000 1800-Watt Portable Induction Cooktop – $99.99
• Whip-It! Professional Cream Whipper – $49.99
• Infrared Thermometer – $47.96
• Distilling Apparatus – $55.12
• Bernzomatic Self-Igniting Torch – $20.89 (fuel sold separately)

In My Dreams…

Some guys dream of sports cars, some guys dream of rotor/stater homogenizers.  Here is the equipment in the kitchen of my dreams. 

• Torbeo Hand-Held Homogenizer – $841.00
  For blending sauces into a consistency that is unachievably smooth using a conventional blender
• Ultravac 250 Vacuum Chamber Packaging Machine – $4600.00
  Step aside, FoodSaver, this is a vacuum sealer for the big boys.
• Polyscience Sous Vide Professional – $799.95
  Hands-down the best sous vide machine I’ve ever tested.
• Vacuum Rotary Evaporator – $9230.00
  For distilling and extracting essential oils.  No more store-bought vanilla extract!
• PacoJet – $3950.00
  Best known for making extraordinarily smooth and creamy desserts.
• Freeze Dryer – $2,000-20,000
  DIY astronaut ice cream!
• Centrifuge – $7000
  For separating and clarifying stocks and sauces.
• Laser Cutter – $30,000
  For making templates, etching and cutting foods

Luckily, the folks at Char-Broil have created The Big Easy Oil-Less Infrared Turkey Deep Fryer, and were kind enough to loan me a unit for testing.  This cooker looks and works just like a conventional turkey fryer, except it uses no oil.  Instead, a ring of gas burners heat up the inside of the cooking chamber, roasting your meat evenly and allowing the fat to drip down, with no risk of flame-ups. 

Rather than test the machine with a turkey, though, I thought I’d try out a few other dishes.  Check out my video review after the jump.

First, I roasted a whole chicken, along with red potatoes on skewers.  This was hands-down the best chicken I’ve ever roasted at home: super-crisp skin, even cooking and juicy meat.  Unlike roasting a chicken in the oven, the skin was crisp and evenly browned on all sides.  Next, I roasted a whole leg of lamb (pre-seasoned, care of Trader Joe’s).  I hung the lamb in the center of the cooker using a pair of metal skewers.  Although the roasting time was about the same as if I had cooked the lamb in a standard oven, it developed a much nicer crust in The Big Easy.  And, cleanup was much simpler too – all the fat dripped into a non-stick tray at the bottom. 

Finally, I put the unit to the test as a bread oven.  I placed a mound of dough (premade, thanks again, Trader Joes) on a preheated salt block and baked it for 35 minutes.  I was hoping for wood-fired oven results – an intense crust and super-quick baking time, but unfortunately, the result was identical to what you’d expect from a standard oven.  Based on my measurements with an infrared thermometer, the inside of the cooking chamber only reaches between 350°F and 450°F – a wood burning pizza oven can be upwards of 900°F.  Still, considering that this $99 device was only designed for turkey frying, it may not be so single-purpose after all!

Char-Broil “Big Easy” Oil-Less Turkey Fryer – $94.99 [Amazon.com]

Then, I came up with another idea… a radical idea.

The blocking issue in all of my trials was that the top layer of the water froze first and prevented the dissolved gasses in the water below to escape during freezing.  As a result, the middle of the cubes ended up cloudy.  However, under circumstances where water is constantly flowing (like in rivers and around glaciers) no such cloudiness occurs.

I filled a tall jar with regular tap water and placed an aquarium pump just below the water line.  The pump was oriented to suck water up from the bottom of the jar and shoot it out at a right angle.  The result: the water below the pump was 100% clear, but the water surrounding the pump’s outflow nozzle was completely cloudy.  Although I could have cut off the cloudy section of the block and cut the clear section into cubes, my criteria for success is that I can create clear ice with no manual intervention during or after the freezing process. 

Next, I thought, “What if I keep the water in motion as it freezes?” extrapolating the concept behind clear river ice.  I bought a vibrating “personal massager” (yeah, you know the subtext) from Bartell’s for $15.  I clamped the massager in place and balanced the ice cube tray on top.  When I filed the tray and turned on the massager, it created cool standing waves in the water (shown above) and made the texture of the water feel like gelatin.  I was hoping this vibration would be sufficient to allow gas bubbles to release during freezing.  After two hours of freezing, the water was still completely clear, but not yet fully frozen.  I was optimistic, and left the tray overnight to freeze.

The next morning, I was dismayed to see that this experiment had failed as well.  Sometime during the late stages of freezing, the ice had turned cloudy in the middle, just like all my other tests.

Next up, I’m going to try to force the ice to freeze from the bottom-up.  My idea is to place a heating pad over the ice cube tray and slowly reduce the heat over a period of hours.  Hopefully, this will ensure that the top layer of water is the last to freeze and all of the trapped gasses can escape.  In the meantime, I’ll just have to cool my drinks with the vibrator cubes.

I bought a box of these magic bacteria and started experimenting.  The instructions recommend using filtered juices that don’t require refrigeration and aren’t artificially sweetened. But, I’m bad at following instructions, and I don’t trust a juice that doesn’t require refrigeration.  I grabbed a bottle of Pink Lemonade, Mango, Blackberry and Sweet Tea from Trader Joe’s.  The pink lemonade worked well – after 48 hours, it was quite fizzy, though I couldn’t really taste the alcohol.  The Sweet Tea fizzed a bit, but also didn’t taste “spiked” – it just tasted awful.  The Mango juice (which wasn’t fully filtered) formed big solid clumps during fermentation.  I’m not sure why, exactly, but they were gross so I filtered them out with cheesecloth before drinking.  Again, some fizz, no buzz. 

The Blackberry juice was the winner by far.  It also developed some solids (even though it was very clear juice to begin with), and you’d never mistake it for wine, but it was delicious.  Think blackberry Lambic, but with an adjusted price of $1.75 per bottle (64oz of juice at $3, $1.50 per packet of yeast, 25oz in a wine bottle).  This is something I’d make again, and certainly something I’d serve to dinner guests or corruptible children. 

The instructions state that you can allow the fermentation to continue longer than 48 hours to achieve up to 14% ABV.  It also recommends using Welch’s or Ocean Spray – I guess we’ll have to agree to disagree there.  To me, the best part of this product is that you’re free to choose great starting ingredients, like a locally-produced cider, or raspberry juice from plants in your back yard.  But for the fun of quick, easy DIY booze, I’ll raise my glass to this product!

Spike Your Juice – $9.99 (or $20 for a 2-pack on Amazon)

I smoked each of the beverages below by submerging the Smoking Gun’s rubber tube in the liquid.  In the case of the wines, it served to both smoke and aerate the drinks (BTW, I never understood why it should be impolite to blow bubbles into your wine – if someone complains, tell them you’re “helping the wine open up.”)  I ran the smoker for about 30 seconds for each beverage, then blew away any lingering surface smoke before tasting. 

The results were surprising…

In order from most awful to best, here are my tasting notes:

As you can see from the tasting notes, sometimes this was just way too much smoke.  However, I think there’s potential for this technique.  I’ve heard of restaurants using hand-held smokers to create dramatic tableside presentations, and I’m sure that somewhere out there, a slick bartender is serving whisky with smoked barrels.  But, as far as I know, this is pretty open territory. 

Next up on the smoked beverages list: coffee, tequila, scotch, milk, Muscat, hot chocolate… if you’ve got ideas, leave ‘em in the comments below.

*Disclosure: The Smoking Gun I am using is on loan from Polyscience

The ball on the far left was made from plain tap water – never boiled, never filtered.  The 2nd ball from the left was made from tap water which I boiled for 3 minutes, then cooled, then boiled again.  The 3rd ball was made from water I filtered through my Brita then boiled once.  The ball on the far right was made from filtered, double-boiled water. 

Can you see the difference in clarity? Yeah, me neither.

My goal was to make clear ice – that is, ice that is totally transparent without any haziness or white fissures.  I know that commercial ice makers use fancy processes like upside down freezing, but several websites propose that you can make your own clear ice just by boiling (or double boiling) water before freezing.  I put this to the test, and as you can see, my results were less than stellar. 

The complication may have to do with the ice ball molds I was using.  The molds are sealed, so it’s possible that some gasses (or evil spirits) weren’t able to escape during the freezing process.  I’ll try again with regular cubes or blocks, but for now, I’m a little pissed that I’ll have to chill my morning gin with cloudy ice.

Calibrating your thermometer is quick and easy.  Many analog and digital thermometers allow you to offset the temperature to adjust for the calibrated value.  However, if your thermometer doesn’t offer an offset function, a piece of blue tape with the delta will work just fine. 

Method 1: Ice Water

1. Fill a glass with ice cubes, then top off with cold water. 
2. Stir the water and let sit for 3 minutes.
3. Stir again, then insert your thermometer into the glass, making sure not to touch the sides. 
4. The temperature should read 32°F (0°C).  Record the difference and offset your thermometer as appropriate.

Method 2: Boiling Water

1. Boil a pot of distilled water.
2. Once the water has reached a rolling boil, insert your thermometer, making sure not to touch the sides or bottom of the pot.
3. The temperature should read 212°F (100°C).  Record the difference and offset your thermometer as appropriate.
   [Note: The boiling point of water will vary with altitude.  Use this handy water boiling point calculator to find the right temperature for your elevation.]

Now that you’ve got a thermometer you can trust, go forth and cook with confidence!

Total kitchen time: 25 minutes

Shopping list:

• 2 salmon fillets, about 15mm thick
• 1 tsp. smoked salt
• 1/4 tsp. freshly ground black pepper

1. Preheat your water bath to 45.5°C.  [Note: Consuming undercooked fish blah blah blah.  Some people will cook their salmon at 39°C, but that’s a little rare even for my taste.  If you’re squeamish, crank up the temp to 52°C.]
2. Remove the skin from the salmon fillets (reserve for frying, if you want.)  Divide the salt and pepper between the fillets and coat both sides.  Place the fillets, together or individually) into vacuum seal bags, but don’t seal them yet.
3. Prepare an ice bath large enough for the salmon fillets in their bags.
4. Load a Smoking Gun with hickory wood shavings.  Insert the exhaust hose into the open end of the bag and fold over the open edge to partially seal the bag.

   

5. Turn on the Smoking Gun and light the wood chips.  Smoke the entire bowl into the bag, retaining as much smoke as possible. 
6. Holding the open end of the bag up, submerge the bag into the ice bath for a few seconds to condense the remaining smoke.  Seal the open end in the vacuum sealer.
7. Cook the salmon in the water bath for 15 minutes.  Remove and serve.

Given the soft texture of the salmon, I thought it would be good to pair it with something crunchy.  I fried kale leaves in grapeseed oil for a few seconds per side (look out for major oil splatter!) and roasted asparagus with olive oil and rosemary salt.  I also fried the leftover salmon skin until it was slightly crispy and used it to wrap the asparagus.  This is one of my new favorite salmon preparations, and I can’t wait to see what else I can instant-smoke!

In the meantime, I thought I’d share a little prediction.  By the year 2020, you’ll be able to purchase the following items anywhere that also carries a George Foreman Grill.  These devices are way out there now – only the most adventurous (and well funded) chefs are using them, but they’re headed to a kitchen near you… along with those jetpacks.

What the hell is it?
A centrifuge.

What does it do?
It spins little vials of liquid around really, really fast. 

What say the white lab coats?
Centrifuges are used for separating out the parts of a liquid by density.  Your doctor probably uses one to separate your blood cells from plasma to, um, look at them and stuff. 

You put food in that thing?
Although centrifuges have already been used for years in industrial food processing (separating cream from milk, separating sugar crystals from their mother liquor), they’re just now starting to appear in the geekiest restaurant kitchens.  Chefs use centrifuges to clarify stocks, sauces and even lime juice.  Even the finest mesh strainer is no match for the separating power of the sedimentation principle, so the next time you’re making consommé consider your centrifuge instead of your chinoise. 

What the hell is it?
A rotary evaporator.

What does it do?
It extracts solvents from substances.  Kind of like a moonshine still, but designed by robots from the future.

What say the white lab coats?
By creating a vacuum inside the glass chamber, the rotary evaporator reduces the boiling point of a compound liquid.  Then, through gentle heating and turning, solvents dissolved in the liquid are evaporated and removed.

You put food in that thing?
Imagine being able to extract the essential flavor from just about anything into a highly-concentrated liquid.  Sure, you can go buy mint extract or even rosemary extract (if you know where to look), but what about the essential oil of bacon or saffron?  Chicago’s famed Alinea restaurant has been using rotovaps to distill the essential oils from herbs, and even chiles – all flavor, no heat.  So, when you’re baking cookies and the recipe calls for vanilla extract, don’t turn to the plastic vial from the grocery store; make your own!

What the hell is it?
It’s a freeze dryer.

What does it do?
It freeze dries, R-tard.

What say the white lab coats?
Freeze drying has all the benefits of freezing, but without those nasty ice crystals.  The freeze dryer freezes the materials inside, then creates a vacuum and adds just enough heat so that the water frozen inside the materials converts directly to gas and escapes.

You put food in that thing?
It may not surprise you to hear that freeze dryers are used for culinary applications.  After all, this was the space-age piece of technology that brought us Astronaut Ice Cream.  But it’s not all about infinite shelf lives and lightweight transportation.  Ferran Adrià, often called the best chef in the world, has been freeze drying slices of fruit at his restaurant El Bulli.  10 years from now, when you want to make apple chips and jerky, you won’t be reaching for the dehydrator – you’ll be freeze drying!

1.  Extra-Long BBQ Tongs.  They don’t sound geeky, but this single piece of equipment can mean the difference between retaining your forearm hair or not.  Look for locking tongs at least 16” long, with metal ends since plastic and even silicone can melt at grilling temperature.

2.  TurboQue Turbo-Charged Smoker.  This battery-operated fan attaches to the inside of your grill and turns it into a convection smoker.  This means reduced cooking time and extra exposure to smoke from wood chips. 

3.  Infrared Thermometer.  Sure, you could hold your hand above the grill grate and count “one Mississippi… two Mississippi,” but it’s far more geeky to be accurate to .1 degrees Fahrenheit.  This non-contact thermometer instantly measures surface temperatures with the pull of a trigger, enticing you to be quick on the draw. 

4.  Instant Digital Probe Thermometer.  While the infrared thermometer will tell you how hot the grill is, it won’t give you a read on the internal temperature of your porterhouse.  Use a probe thermometer to quickly check the doneness of thick cuts without having to slice them open.  Choose a digital instant read over an analog model, unless you enjoy waiting while your fingernails melt over the fire.

5.  Onion Goggles.  You may look a little… special… flipping burgers with these on, but if you’re cooking with smoke, or better yet, over a campfire, they are indispensable.  The foam-lined glasses are highly effective at keeping the smoke out of your eyes, and keeping girls from ever talking to you.  But hey, form follows function, right?

I’ve recently been fascinated by the idea of sous vide cooking – a method of slowly cooking vacu-sealed foods in a precisely controlled water bath to achieve the optimal doneness.  Last year, Sur La Table started carrying the world’s first “home” sous vide cooker, the SousVide Supreme.  This was fantastic, since commercial sous vide cooking machines cost north of $2000.  However, the home model (priced at $450) is still a steep investment for something that essentially just keeps water warm.  I was determined that I could build a better device on-the-cheap.

Behold, the $75 DIY sous vide heating immersion circulator!  By scrapping together parts that are readily available on eBay and Amazon, I was able to build a self-contained device that heats and circulates water while maintaining a temperature accurate to .1 degree Celsius (yes, point one degrees!).  And unlike the SousVide Supreme, my device can be mounted onto any container (up to a reasonable size, perhaps 15 gallons) allowing you more room to cook, if needed.

To build your own device, you’ll need some basic soldering skills, the list of stuff below, about 6 hours of free time (plus time for glue to dry) and the can-do attitude of a geek who doesn’t want to pay $450 for a water heater.  Click the “more” link for complete step-by-step instructions.

If these instructions have helped you build you own machine, I hope you’ll consider donating.  My goal is to mass-produce the world’s first sous vide heating immersion circulator for under $100, and every donation helps!

Makes: 1 sous vide immersion heater
Total tinker time: about 6 hours

Shopping list:

• Clear Storage Container – Medium $4.95
• 3x NORPRO 559 Immersion Heater for Warming Liquids $17.97
• 79 GPH Fountain, Hydroponics, or Aquarium pump- VA80 $9.99
• PID Temperature Controller with SSR Output $39.50 (I’ve found similar controllers on eBay for under $30.00, but this one is very popular among builders of this project)

Note: Make sure the controller you purchase has an SSR or Voltage output.  Controllers with a relay-only output will require an external relay and different wiring than what is listed in this project.

• PT100 Thermocouple Probe $5.99
• SPST Heavy-Duty Rocker Switch $2.99
• 7-9VDC/12A SPDT Relay $4.49  (Only use if you have a CD101 PID controller and want to save a few bucks over buying the SSR)
• 25A Solid State Relay, DC Input, AC Output $14.50 (Necessary for the JLD612 PID Controller)

I’ve updated the parts list to specify an SSR – it adds a little to the cost of the project, but it is far more reliable, easier to connect, and works with any SSR/Voltage-output PID controller.

• 1 piece of 1/4” acrylic, about 5cm x 20cm
• 1/4” x 2” eye bolt and nut
• About 2’ of 16-18 gauge wire
• 3 wire nuts
• Electrical tape
• A means of cutting acrylic (see article)
• Soldering iron and solder
• Multimeter (tool that measures voltage, current, resistance)
• Hobby knife (X-Acto or similar)
• Tub and Tile Silicone Caulk
• Hot glue gun
• Krazy Glue

Step 1 – Making cutouts in your enclosure

This is the most difficult part of the whole project.  In order for the final assembly to be sturdy, water-resistant and decent looking, you’ll need to cut your mounting holes as precisely as possible.  I am very lucky to have access to a laser cutter at a lab at work, which makes this kind of precision cutting very easy and accurate.  However, in the absence of a $30K computerized laser cutting machine, with a steady hand, you can achieve the same results using a high-speed rotary tool like a Dremel.

I’ve included a cutting template that is matched to the heaters, PID controller and switch in the shopping list.  However, if you use different parts (different models, different manufacturers) you’ll need to adjust the template to ensure a tight fit of all parts.

Click here for the 1:1 scale diagram (PDF)

1. Pick a side of the storage container that you want to be the bottom.  Using the template as a guide, cut out the three holes for the immersion heaters.  Make sure that these holes are closest to the open end of the container (the end that has the lid) to ensure you’ll be able to reach inside later for wiring, etc.
2. Next, cut the small oval-shaped hole for the water pump power cord.
3. Turn the container over so the side with the holes is facing down.  Now, cut out the openings for the PID controller, the on-off switch, and the power cord.  Be sure that the hole for the PID controller is towards the top.  Otherwise, you’ll be cramped for space when trying to reach the back of the controller. 
4. Next, dry-fit all of the parts to ensure a good, snug fit.  The tighter the fit, the more sturdy the finished product will be.

Step 2 – Making the mounting bracket and pump holder

The mounting bracket is a J-shaped piece of acrylic that will let you attach the finished sous vide cooker to the side of a pot or basin.

1. Cut out the rectangle on the 2nd page of the parts diagram and drill the hole as indicated.
2. Find a rectangular surface that will allow you to make the 2 90-degree bends necessary to shape the acrylic into a “J”.  I used a small, glass olive oil bottle with flat sides and rounded corners.
3. Turn on your stove.  Holding the long end of the acrylic with an oven mitt, warm it a few inches above your stovetop, turning to heat both sides.  It may take a few minutes for the acrylic to be warm enough to bend- you’ll know you’re getting close when the acrylic starts to curl away from the heat.
4. Bend the acrylic along (approximately) the lines indicated in the diagram to form a “J”.  Press the bottom part of the J (not the side with the hole, and not the long side) against a flat surface such as your counter top.  Immediately cool the acrylic with cool water to hold its form.

Step 3 – Mounting the immersion heaters

The immersion heaters are the primary working element of the sous vide machine.  We’ll mount them hanging down from the bottom of the enclosure, and arranged so that the opening in the middle of the coil is lined up between all three heaters.

1. Cut the power cord off of each heater, leaving about a 4” tail of wires from the heating end.  Keep one of the long lengths of power cord (including the plug) to use later as the main power cord. 
2. Using your hobby knife, scrape down the flat sides of the heater handles to remove lettering and to flatten out the circular rim at the top of the handle.  This will allow for a deeper and tighter fit in the heater openings.
   
3. Arrange all three heaters in their respective openings.  Note that the heaters should be oriented such that the coils are facing towards the center-line of the enclosure.  You should be able to fit your finger down the middle of all three coils.  Make sure the heaters are snug in their openings.
4. Apply a small bead of tub and tile caulk around the heaters on the outside of the enclosure.  Allow to dry overnight before proceeding.

Step 4 – Wiring

CAUTION: Don’t ever power on the heater coils unless they are submerged in water!  Also, don’t electrocute yourself.

If you have experience with basic circuitry and wiring, this will be pretty easy.  However, if you’ve never worked with a soldering iron or circuit diagrams, these steps will take you a while.  Refer to the wiring diagram below for the “big picture.”

Wiring diagram for JLD612 PID Controller with SSR

Wiring Diagram for CD101 PID Controller with physical relay

Update: I’ve updated the wiring diagram to make it clear that the view of the relay posts is from below.  In other words, if you set the relay down on your table with the pins facing up, that will match the alignment in the wiring diagram.

1. Strip off about 1/4” of shielding from your power cord (remember, the cord that you saved from one of the immersion heaters?).  Run the power cord in through the power cord opening on the front of the enclosure.  Separate the 2 wires about 6”.  One of these wires will go through the power switch, and the other will go directly to the PID controller, heaters and pump.
2. Use your multimeter to find the two posts on the back of the power switch that are normally open, but closed when the switch is on.  On my power switch, these were the far and middle posts (not the two posts closest to the “ON” side of the switch, you know, with the dot). 
3. Pass the switch mounting nut (the thing that screws on the back) over one lead from the power cable, inside the enclosure.  Run the lead out through the power switch hole.  Solder that lead to one of the posts you identified in step 2.  Cut an 8” length of wire and solder one end to the 2nd lead on the switch.  Tuck the wires inside the enclosure, place the switch in its hole, and tighten the mounding nut to secure it in place.  You’re now done with the power switch.
4. Next, wire together the heater leads.  Separate the leads from the heating coils.  Gather together one lead from each coil to make two bundles of three.  Cut two 6” lengths of wire and add one to each bundle.  You should now have two bundles, each with four wires – 3 of which go to the heaters, and one left dangling.  Solder the wires in each bundle together, then cap with a wire nut and some electrical tape.
   
5. Of the leads you have coming out of the heater bundles, one will go straight to the incoming power, and the other will go to the relay that turns on and off the heaters.   
6. At this point, it gets too difficult to describe the rest of the wiring in words, so refer to the wiring diagram.  Just make sure to be aware of how everything will mount in the enclosure when you’re all done.  Pass the wires through the mounting ring on of the PID controller before attaching them to the terminals, etc.
7. After wiring the connections to the relay (or SSR), coat the bottom with hot glue to surround the connection points.  This will act as an insulator and prevent the relay from shorting out against any metal inside the case.  Or, if your SSR came with a plastic cover, secure it in place to prevent the connections from shorting.
8. If you are using the PT100 thermocouple (which I recommend), make sure you connect the leads exactly as shown in the wiring diagram or you will have an inaccurate temperature reading.  (There’s no instruction manual with these probes, so it took 30 minutes of trying different combinations before I found the right one).

Step 5 – Final Assembly

1. Using Krazy Glue, glue the J clamp to the bottom-front of the enclosure.  Wait until dry before proceeding.
   Note: This glue joint is a popular point of failure.  If you’d like, strengthen the connection between the J clamp and the body by using two screws and nuts.
2. Glue the nut for the eye bolt to the inside of the hole in the J clamp.  Ensure that the nut lines up with the hole so the eye bolt can pass through. 
    
3. Seal the openings for the power cord and pump cord using tub and tile caulk.
4. Put the back cover on the enclosure and wrap the seam with electrical tape.
5. Stick the suction cup feet of the immersion pump to the flat end of the J clamp and position the water outlet to pump through the middle of the heating coils.

Step 6 – Testing

Now that everything is wired up and assembled, you probably want to see if it works.  WAIT!  Don’t turn the machine on (ever!) unless the coils are submerged in water or, they will burn out in about 5 seconds (I learned this the hard way). 
To test the machine out, fill a basin with water so that it covers at least the coil part of the heaters.   Mount the machine on the edge, so that the J clamp hangs over the lip.  Tighten the eye bolt to secure the machine.  Plug in the cord and flip the power switch!  If the PID controller turns on and the pump starts pumping, that’s a good sign!  Note that the heaters may not warm up just yet, depending on what the target temperature is by default.

Step 7 – Programming the PID Controller

For users of the JLD612 PID Controller

For programming instructions such as running Auto-tune and changing alarm values, refer to the JLD612 manual.  Here are the steps you should take when programming your controller for the first time.

1. Press SET and enter code 0089, then press SET.
2. Set the value of Inty to Pt10.0 to get the temperature to display with one decimal place.  (I had to set it to Pt100, then back to Pt10.0 to get this to work the first time.
3. Select End to exit the programming menu.

For users of the CD101 PID Controller

Out-of-the-box, the PID controller is designed to work with a different type of thermocouple, so the readings that you get using a PT100 will be strange.  Follow the instructions in this manual (that doesn’t ship with the PID controller) to set it for the PT100 probe.  You can also follow the instructions there to set the number of decimal points of precision.

Next, set a target temperature by tapping the SET button, then using the up and down arrows to pick a number and pressing SET again to confirm.  50C is a good target temp.  The OUT1 light will light up, indicating that the PID controller is turning on the heater.  You should hear a soft clicking noise – this is the relay kicking in.  At this point, the heating coils are on and warming up.  As the temperature measured by the probe (green, top line) approaches the target value (orange, 2nd line), the relay will click on and off more frequently to sustain the temperature..

Ideas, Improvements, Thoughts

After burning out my first set of heating coils, I realized that there must be a better method of heating the water.  The coils are very effective and heat the water very quickly.  However, I’m pretty paranoid about burning them out again, and they’re a pain to replace.  I’ve found some commercial immersion heating elements, but they’re about $100, which inflates the budget for this project by quite a bit.  I may try using the heating element and pump system from an old espresso machine, the kind that makes steam.  Since it already has a self-contained heater and an pump, it might even be cheaper than the heating coils and aquarium pump.

I’ve also thought about turning this machine into a general-purpose temperature control unit.   Instead of wiring the heaters directly to the relay, I would install a power outlet on the back of the enclosure and add a jack to plug in an external temperature probe.  If I wanted to use the immersion heaters, I’d just plug them in to the power outlet.  If one got fried, I’m only out $6 instead of an hour of removing glue and solder.  Also, a general-purpose temperature controller is great for making your own smoker box.  A-la Alton Brown, you can plug in a hotplate filled with wood chips and have a precisely temperature-controlled smoker for just a few bucks.

I’m thrilled to start playing with sous vide cooking, and I’m happy that I was able to build an accurate, reliable machine for $75.  Even the PID Controller + Crockpot method costs $185 (not including the Crockpot!).

Troubleshooting

I gotten a lot of emails and comments asking for troubleshooting help, and rightfully so – there’s a lot going on in this project, especially if you’re pretty new to DIY electronics.  I’ve decided to add my basic troubleshooting routine, which should hopefully get you sorted out.  If you still have problems, please post a comment below, or send me an email at scott@seattlefoodgeek.com.

If your heaters don’t get hot when they should (i.e., your machine isn’t working), do the following:

1. Ensure that your OUT1 light goes on and off when it should.  It should be on when the unit is heating, and off when you’re at or above the set value.  If not, double check that you’ve set your temperature probe type correctly, and that OUT1 is set to heating mode in the PID settings menu.  If this looks correct, proceed to step 2.
2. Verify that your PID controller has an SSR/Voltage output.  This should be specified on the sticker on the side of your PID controller.  The controller in the photo below only has a relay output (this is not what you want).
   
   PID controllers generally have two types of outputs: relay and voltage.  Contrary to how it sounds, a relay output is not used for controlling a relay.  Rather, a PID controller with a relay output actually has an internal relay.  Unfortunately, the internal relay is typically not rated for the kind of load that the heating coils pull, so you cannot connect them directly to the internal relay.  A PID controller with an SSR/voltage output produces a DC voltage (8-12V DC) that we can use to control an external mechanical relay or a solid state relay (SSR).  That’s what we want.
   Telltale signs that your PID controller has a relay-only output: a) there’s no voltage across pins 5&6 (or the corresponding pins on your controller) when the OUT1 light is on, b) you hear a clicking sound when OUT1 turns on and off, even when your external (blue) relay is disconnected, and c) you measure continuity across the pins that correspond to OUT1 when OUT1 is on.
   If you have a PID controller with a relay output, not all is lost.  You’ve got two options:
   1)  Return it for a PID controller with an SSR/voltage output, or
   2)  Use the internal relay to control an external 120VAC relay that is rated for 8+ Amps @ 120VAC.  The wiring for this configuration is a little messier, and you’ll need to buy a different relay than the one specified in the parts list.  The wiring diagram for this configuration is below.  Note that I haven’t attempted to show the actual pin configuration of the external relay – rather this is the logical way you’ll need to wire it in.  
   
   If you’re sure that your PID controller has an SSR/voltage output, proceed to step 3.
3. Verify that you are using the right kind of relay for your PID controller. The CD101 will work with either an SSR (solid state relay) or a physical relay. However, the JLD612 and many other PID controllers will only work with an SSR.
4. If you’re using a CD101 and a physical relay, ensure that your external (blue) relay is wired correctly.  You should hear a clicking noise coming from that relay when OUT1 lights up or turns off.  If not, you may have connected the leads from pins 5 & 6 backwards, or your external relay may require a higher activation voltage than what your PID controller outputs.  Measure the voltage from pins 5 & 6 and compare to the coil voltage specified by your relay.  In practice, there is some wiggle room (ex., a relay with a 9V coil will often be activated by less than 9V).  If the PID doesn’t produce enough voltage, buy an SSR.  If your relay is clicking, proceed to step 5.
5. Check for 120VAC going to the heater leads when OUT1 is on.  If you’re not seeing a voltage, check the connections across your relay and between pin 1 and your heaters.  If you’re getting 120VAC to your heater bundles, proceed to step 6.
6. Your heaters are likely burnt out.  This can happen in a flash if you accidentally supply power to the heaters when they are out of water.  Double check by submerging your heaters and connecting an 120VAC power source directly to the leads (exercising great caution not to electrocute yourself).  If they heat up, you’ve got a loose wire somewhere in your connections.  If they don’t heat up, they’re burnt out and you’ll need to replace them.

If these instructions have helped you build you own machine, I hope you’ll consider donating.  My goal is to mass-produce the world’s first sous vide heating immersion circulator for under $100, and every donation helps!

I’m a huge geek, and I love carving pumpkins.  So, when I found out that I had access to a 30W CO2 cutting laser, there was only one thing that came to mind: laser-carved pumpkins.  Every October, I spend a few weeks in the lab working on new techniques for perfecting my laser pumpkins.  Below is a research paper I wrote detailing the process.  It might be a little dry, but the results are, well, scary!  And, in case you haven’t seen the results, here are my laser-carved creations from the past few years.

Aims

The purpose of this document is to communicate the results of research relating to laser etching the surface of pumpkins. I will describe the heuristics I developed for successful and repeatable etching. Additionally, I will suggest new possible approaches and applications of my research that may produce patentable processes with broader-reaching applications than pumpkin etching.

Rationale

I originally began this research to fulfil a personal hobby – pumpkin etching. For the last several years, I have been creating pumpkin versions of fine art paintings by hand. My prior method involved

· preparing an image for etching using digital photo editing software,

· transferring the design to the pumpkin by means of tracing,

· removing the outer flesh of the pumpkin in the areas of negative image space,

· and, illuminating the pumpkin from the interior to provide a high-contrast effect.

Although the manual method has been very successful, it is limited in two primary ways:

1. The entire process, even for a simple image, takes upwards of 90 minutes to complete.

2. The level of detail and accuracy of the shapes in the image is limited by human precision and patience.

However, using a computer-controlled device to produce the etched image overcomes these limitations. A CO₂ laser cutter and engraving machine suits this application quite well.

Methods

I prepared images for laser engraving by employing various image manipulation techniques. Then, using a laser cutter, I engraved the images on to the surface of pumpkins. By managing the speed, power and distance from the focal point I was able to optimize the quality of the final etchings.

Future Research

I believe that a spiral method of engraving may be more efficient than the 2-axis engraving method. I propose that a design for a spiral-based engraving technique may be patentable.

Materials and Methods

Materials

• Laser Cutter and Engraver
  • LS Model M-300
  • 50 Watt CO₂ Laser
  • 2” and 4” focal length lenses
  • 12”x24” cutting area with 8” of vertical clearance
  • Adjustable-height cutting table
  • Air-cooled cutting head
  • Red Dot Pointer
• Pumpkins
  • 6-8” Sugar Pie pumpkins
    • Spherical
    • Medium-dark orange flesh
    • Shallow ridges
  • 3-5” Jack Be Little pumpkins
    • Flattened shape
    • Orange flesh
    • Deep ridges
• Software
  • Adobe Photoshop CS3 (image authoring)
  • Adobe Illustrator CS3 (vector transformation)
  • CorelDraw

Image Preparation

The first step in the etching process is to prepare the source images. This step is critical to the success of the pumpkin. Over-detailed or overcomplicated images do not present well, particularly on the small pumpkins that the laser could accommodate. Therefore, it is necessary to prepare ones artwork thoughtfully before etching. I used a variety of image sources for my designs (scanned images, digital photos, vector graphics) but I needed to reduce all of the images to black and white. I employed one or more of the following techniques to create an “etchable” image:

Color Flattening
This is the simplest method of image preparation. Simply open a color image in Photoshop and change the image mode to black and white.

Color flattening works well on images that were originally black and white. However, this technique will not always work well on images that depend on color information. For example, human faces often end up missing critical details.

Thresholding
The thresholding method converts the source image to black and white based on the luminosity of each pixel. Bright areas will end up as white and dark areas will end up as black. To apply, open an image in Photoshop and choose Image > Threshold. Then, adjust the slider on the histogram to change the luminosity threshold.

This method is very effective on evenly-lit images. However, if an image contains a shadowy area, all of the detail in that region will be lost by the threshold. Partition the image into sections or blend multiple thresholds together by duplicating the source layer to avoid detail loss in dark areas.

Stamping
This method uses a built-in Photoshop filter to convert an image to black and white. From the Filters menu, select Sketch > Stamp. Adjust the brightness threshold similarly to the thresholding technique. Adjust the detail slider to produce an image with bold, whole shapes while avoiding “outliers” and areas of floating pixel islands.

Stamping is a useful method for hand-carving as well as computerized etching. Since stamping reduces the number of whole shapes in the image, it produces more striking pumpkins when viewed at a distance. However, stamping is also likely to lose key details of your image, and ultimately affect the recognisability of your artwork.

Halftoning
Halftoning is a method that will be familiar to comic book and magazine readers. If you look at most printed publications with a magnifying glass, you’ll notice that the images are actually composed of groupings of dots. These dots are discrete shapes, and therefore they can be etched by the laser. Halftoning is a more complicated process than the other image preparation methods. For more information, view this tutorial.

Vector Tracing
This method converts a bitmap into a vector graphic by finding the dominant shapes in the image and transforming them into paths. Open an image in Adobe Illustrator and select Object > Live Trace. Adjust the threshold, blur, path fitting and minimum area settings to produce a vector version of your image.

Vector tracing results in extremely clean, sleek images. However, since it is based on selecting a threshold value, it suffers the same contrast issues of our standard thresholding method. Vector tracing is often effective when combined with a secondary method.

Haloing
Haloing is a process for outlining an image with a thick dark line. Haloing is necessary for images that have un-etched areas at their outermost boundaries. Without a stroke outline, the un-etched areas would blend in to the rest of the pumpkin and information about the image would be lost.

Note: Haloing should be done as a last or next-to-last step (following inversion). If you are haloing a positive (non-inverted) image, you will need to add a white outline. This also requires that the background of your image is transparent, as opposed to white. If you are haloing an image that has already been inverted, you will need to add a black outline.

In Photoshop, open your image. Select the layer you wish to outline in the layers window. Right-click and choose Layer Effects. Select Stroke in the next screen and adjust the settings until you have a thick line of the appropriate color. If your final image will measure 5” on the pumpkin, choose a stroke width of at least 1/8”.

Inversion
Inversion is the process of reflecting color values across the spectrum origin. For black and white images, everything that is black becomes white and vice versa. This is a critical final step for any images being etched onto a pumpkin. The laser will etch any black (dark) areas of the image, removing the outer flesh. However, on the pumpkin, these areas are actually lighter than the surrounding negative space. In order for images to appear positively on the pumpkin, you must invert your final image before processing.

In Adobe Photoshop, open your completed image. Then select Image > Adjustments > Invert.

Etching

Power, Speed and Focus
To produce the highest quality etchings, there were three independent variables that I needed to optimize: 1) the power output of the laser, 2) the speed at which the laser moved, and 3) the distance to place the pumpkin from the focal point of the laser.

Figure 1 – Power and speed test pattern

The image on the left shows an early test pattern. Each horizontal stripe shows the results of different combinations of power and speed. Although the stripes appear black (burned), the dark coloration wiped off easily with a damp cloth.

After numerous trials, I determined that using power and speed settings of 100% produced the best results. By far, the most critical factor in successful etching was the focal distance.

Burning
During my trials, I primarily used a two inch focal length lens for the laser. The cutting head of the laser was also equipped with an air cooling nozzle. This nozzle was vitally important to successful etchings. Since pumpkins are composed of organic material, they turn into carbon ash when they are burned. This is what turned the pumpkin in Figure 1 into a series of dark lines instead of revealing the lighter flesh below the skin. In to achieve the optimal etching, you must balance the focal length with the effective range of the air nozzle. As it turns out, the nozzle only prevents burning in a narrow window of distance, about one inch from the origin.

Figure 2 – Ideal distance for etching

Figure 2 shows the proper etching distance to produce an un-burned, etched pumpkin. Pumpkins placed between ¼” and 1” from the nozzle will etch well, with little or no burning. Pumpkins placed between 1” and 2” from the nozzle will suffer some burning, but the black areas are easily cleaned with a damp cloth. Pumpkins placed more than 2” from the nozzle will from permanent damage, such as burning and scarring. Scarring occurs when the laser is not sufficiently focused to vaporize the outer layers of the pumpkin flesh. As a result, the flesh turns white and develops a hard crust – a natural healing defence of gourd vegetables.

Spherical Distortion and other Consequences
Due to the near-spherical nature of pumpkins, achieving a uniformly-deep, unburned etching proved quite difficulty. However, I did develop a few strategies that overcame most of the challenges I faced.

Figure 3- Original and distorted images

Spherical distortion occurs when one projects an image from a rectilinear source onto a curved surface. In our case, we are projecting (one pixel at a time) a flat image onto a sphere-like pumpkin. The image on the left shows the “barrelling” effect of such a projection.

For most designs, this type of distortion was not an issue. Since the distortion is proportional to the distance from the origin, only very wide or very tall images suffered any noticeable distortion effects. However, these effects are avoidable using pre-etching image correction. In Photoshop, click Filters > Distortion > Spherize. Then, choose a negative value to offset the barrelling effect of the pumpkin.

Figure 4- Spherical Burning caused by focal distance

Spherical burning occurs when the curvature of the pumpkin causes the distance between the center of the image and the outer boundaries of the image to pass through the “ideal” zone of burning distance. For example, if I set the top-most spot of the pumpkin ¾” from the cutting nozzle, the outer sections of the pumpkin may be 1.5”-2” away from the nozzle, causing them to burn.

To combat this, I manually adjust the height of the cutting platform during the etching process. All images on the laser are etched from top to bottom, starting from the origin and moving in a negative Y direction. At the beginning of the etching, I adjust the platform so the top of the pumpkin is in the “green” zone. As the etching continues in the negative Y direction, I lower the platform by .05” at a time until I reach the crest of the curvature. Adjusting the platform height in larger increments than .05” causes visible differences in the cutting depth. Once the laser reaches the topmost section of the pumpkin, I manually raise the platform in the same increment until the etching is complete.

This technique is very effective for combating spherical burning, but it suffers from the following limitations:

· If the platform height is set such that the cutting nozzle is lower than the topmost section of the pumpkin, there is a risk of bumping into the pumpkin when the nozzle moves across the work area.

· This technique is effective against vertical burning, but does not address the same problem laterally.

· The technique requires manual intervention, which reduces the value proposition of automated etching.

[Dornob via Gizmodo]