Cooking for Geeks: Real Science, Great Hacks, and Good Food

by Jeff Potter

  I often cook steak tips at the same time that I preheat bok choy, Swiss chard, or other hearty greens, using the same water bath for both the steak and the veggies. This works because the veggies don’t actually cook at the temperature that the meat is cooking at.

  This technique works great for small dinner parties. I bag and seal the steak tips just before my guests show up, and once they arrive, I drop the bag of steak tips and some bok choy into a water bath set to 140°F / 60°C. Thirty minutes or so later—after catching up with my guests, sharing a beer or glass of wine, and noshing on cheese and bread—I pull the steak tips out and let them rest for a few minutes, during which time I quarter the bok choy and steam it in a hot frying pan.

  Because the bok choy is already warm, it reaches a pleasant cooked texture in two to three minutes, at which point I transfer it to the dinner plates. Reusing the same frying pan, I quickly sear the outside of the steak tips, which I then cut and transfer to the plates. Total time spent while guests wait? Five minutes, tops. Number of dirty dishes? One, plus plates. And it’s delicious!

  Enhancing texture

  Ever wonder why some vegetables in canned soups are mushy, textureless blobs, but others aren’t? Some vegetables—carrots, beets, but not potatoes—exhibit a rather counterintuitive behavior when precooked at 122°F / 50°C: they become "heat resistant," so they don’t break down as much when subsequently cooked at higher temperatures. Holding a carrot in a water bath at around 120°F / 50°C for 30 minutes causes enhanced cell-cell adhesion, science lingo for "the cells stick better to each other," which means that they’re less likely to collapse and get mushy when cooked at higher temperatures.

  During the precooking stage, calcium ions help form additional "crosslinks" between the walls of adjoining cells, literally adding more structure to the vegetable tissue. Since "mushy" textures occur because of ruptured cells, this additional structure keeps the vegetable tissue firmer by reducing the chance of cellular separation.

  The normal solution to mushy vegetables is to refrain from adding them until close to the end of the cooking process. This is why some beef stew recipes call for adding vegetables such as carrots only in the final half-hour of cooking.

  For industrial applications (read: canned soups), this isn’t always an option. In home cooking, you’re unlikely to need this trick, but it’s a fun experiment to do. Try holding carrots at 140°F / 60°C for half an hour and then simmering them in a sauce mixed in with a batch of sliced carrots that hasn’t been heat-treated. (You can cut the heat-treated carrots into slightly different shapes—say, slice the carrot in half and then half-rounds, versus full-round slices—if you don’t mind your experiment being obvious.)

  Chocolate

  Tempering chocolate—the process of selectively melting and solidifying the various forms of fat crystals in cocoa butter—can be an intimidating and finicky process. The chocolate must first be melted to above 110°F / 43°C, then cooled to around 82°F / 28°C, and then heated back up and held between 89°F / 31.5°C and 91°F / 32.5°C. Once tempered, you must play a thermal balancing act: too warm, you lose the temper, and too cold, it sets.

  It’s not exactly correct to describe chocolate as something that "melts," because chocolate is a solid sol, a colloid of two different solids: cocoa powder and cocoa fats. The cocoa powder itself can’t melt, but the cocoa fats that surround it can. Cocoa butter contains six different forms of fats, and each form melts at a slightly different temperature.

  The six forms of cocoa fat are actually six different crystalline structures of the same type of fat. Once melted, the fat can recrystallize into any of the six forms. It’s for this reason that tempering works at all—essentially, tempering is all about coercing the fats to solidify into the desired forms.

  Melting points of the six polymorphs of cocoa fat.

  Note

  How do scientists tell when something is melting? Two common techniques are used: differential scanning calorimetry (DSC) and x-ray diffraction. In DSC, energy is added to a closed system at a controlled rate, and the temperature of the system is monitored. DSC picks up phase changes (e.g., solid to liquid) because phase changes require energy without a temperature change. X-ray diffraction looks at how x-rays scatter when passed through a sample: with each phase change, the x-ray pattern changes.

  It’s not a matter of different types of fats; it’s the structure that the fat takes upon solidifying that determines its form. Two of these forms (Forms V and VI) link together to create a metastructure that gives chocolate a pleasing smoothness and firm snap when broken. Chocolate with a high number of Form V structures is said to be tempered. The other primary forms (I–IV) lead to a chalky, powdery texture. Form VI occurs in only small quantities, due to the temperature range at which it crystalizes. Chocolate that has been exposed to extreme temperature swings will slowly convert to Forms I–IV. Such chocolate is described as having bloomed—the cocoa particles and cocoa fats separate, giving the chocolate both a splotchy appearance and a gritty texture.

  To further complicate things, the fats in cocoa butters don’t actually melt at an exact temperature, and the composition of the fats varies between batches. The ratio of the different fats determines their exact melting point, and the ratio varies depending upon the growing conditions of the cocoa plant. The fat in chocolate from beans grown at lower elevations, for example, has a slightly higher melting point than chocolate from beans grown at higher, cooler elevations.

  Still, the temperature variances are relatively narrow, so the ranges used here generally work for dark chocolates. Milk chocolates require slightly cooler temperatures, because the additional ingredients affect the melting points of the different crystalline forms. When looking at chocolate for tempering, make sure it does not have other fats or lecithin added, because these ingredients affect the melting point.

  Luckily for chocolate lovers worldwide, chocolate has two quirks that make it so enjoyable. For one, the undesirable forms of fat all melt below 90°F / 32°C, while the desirable forms noticeably melt around 94°F / 34.4°C. If you heat the chocolate to a temperature between these two points, the undesirable forms melt and then solidify into the desirable form.

  The second happy quirk is a matter of simple biology: the temperature of the inside of your mouth is in the range of 95–98.6°F / 35–37°C, just above the melting point of tempered chocolate, while the surface temperature of your hand is below this point. Sure, a certain sugar-coated candy is known to be made to "melt in your mouth, not in your hands," but with properly tempered dark chocolate, the sugar coating isn’t necessary (it is necessary for milk chocolate, though, which melts at a temperature lower than that of your hand).

  Note

  M&Ms were developed in 1940 by Frank C. Mars and his son, Forrest Mars, Sr. During the Spanish Civil War (1936–1939), Forrest saw Spanish soldiers eating chocolate that had been covered in sugar as a way of "packaging" the chocolate to prevent it from making a mess.

  How does all of this relate to sous vide cooking? Traditional tempering works by melting all forms of fat in the chocolate, cooling it to a low enough temperature to trigger nucleation formation (i.e., causing some of the fat to crystallize into seed crystals, including some of the undesirable forms), and then raising it to a temperature around 90°F / 32.2°C, where the fats crystallize to make Form V crystals.

  This three-temperature process requires a watchful eye and, during the second step, constant stirring to encourage the crystals to form while keeping them small. Water baths allow for a shortcut in working with chocolate: already tempered chocolate doesn’t need to be tempered if you don’t get it any hotter than around 91°F / 32.8°C. The desirable forms of fat won’t melt, so you’re good to go. To melt already tempered chocolate, seal it in a vacuum bag and submerge it in a water bath set to 91°F / 32.8°C. (You can go a degree or so warmer; experiment!) Once it’s melted—which might take an hour or so—remove the bag from the water, dry the outside, and snip off one corner:
instant piping bag.

  Temperature versus time chart for melting and tempering chocolate.

  If you’re going to be working with chocolate on a regular basis, the sous vide hack will probably get tiring. It works, but if you have the dough to spend, search online for chocolate tempering machines. One vendor, ChocoVision, sells units that combine a heat source, a motorized stirrer, and a simple logic circuit that tempers and holds melted chocolate suitable for everything from dipping fruit to coating pastries to filling chocolate molds. Of course, if you have a slow cooker, thermocouple, and temperature controller...

  Chocolate Almond Bars

  My local grocery store recently started carrying specialty bars of chocolate infused with unusual ingredients: curry powder and coconut; plums, walnuts, and cardamom; even bacon bits. These exotic chocolate bars also carried exotic price tags, so I thought: how hard can it be to make these? With sous vide, it turns out it’s downright simple.

  Place tempered chocolate in a vacuum bag. Use chocolate in bar form; chocolate chips might not work if they aren’t as well tempered.

  Add your flavorings. Try almonds or hazelnuts (at about a 1:2 ratio—one part nuts to two parts chocolate by weight). Your ingredients should be dry. Any water in them will cause the chocolate to seize up.

  Seal, drop in a water bath set to 92°F / 33.5°C, and wait for chocolate to melt, which may take an hour or two.

  After the chocolate is thoroughly melted, work the bag to distribute the chocolate and flavorings. You can use a rolling pin to work the fillings around if using something like nuts.

  Let bag rest on counter to cool.

  Once cooled, snip the bag open and peel it off the chocolate. You can break the bar up into pieces.

  Try using coffee beans (yum), candied grapefruit rind, dried fruits such as cranberries, or a mix of toasted nuts (almonds, pistachio, and pecans, and maybe a pinch of cayenne pepper).

  Flash Pickling with a Vacuum Sealer

  ...or How to Void Your Warranty in Three Easy Steps

  Once you have a sous vide setup, you also have most of the tools needed to do flash pickling. In the culinary world, flash pickling refers to submerging a food item in a liquid-filled container, evacuating the container, and then repressurizing the container. Unlike traditional pickling, which requires time (or heat) to coerce the pickling liquid into the food, flash pickling is instant, hence its name.

  Under vacuum, microscopic air pockets in foods like sliced apples and cucumber wedges lose their air. Upon returning to atmospheric pressure, the food expands back out to its original shape, a bit like a sponge. But because the food is submerged, liquid is pulled back in, instead of air. Why bother? Because "Manhattan apples" (use whiskey) or "martini pickles" (use gin) are just plain awesome. See http://video.nytimes.com/video/2007/12/04/magazine/1194817116911/the-edible-martini.html for a video of Dave Arnold talking about the process using a commercial vacuum sealer.

  Cucumbers being flash-pickled in gin using a consumer jar sealer attachment.

  The pros, who use commercial vacuum chambers, can just drop the food into the liquid bath and clamp down on the lid. For the rest of us, though, generating a sufficiently strong vacuum isn’t so easy. But if you have a vacuum food sealer and don’t mind voiding your warranty, there is a way.

  Note

  I should have just written an entire chapter called "Voiding Your Warranty."

  Consumer vacuum sealers have a pressure switch that triggers them to stop pumping and start sealing, meaning that they stop short of creating a strong enough vacuum to create a good pickle. But if you disable the pressure switch, the unit should continue to pump indefinitely, or until the motor burns out.

  To make a DIY flash-pickling system, start with a consumer vacuum sealer. You’ll need a toggle switch and an extra piece of wire, along with a screwdriver and wire cutters.

  Start by popping open the vacuum sealer. It should look something like this.

  Locate the pressure switch (highlighted on left). Cut one of the wires that runs back to the circuit board and interpose a toggle switch (highlighted on right). Cut a small hole in the plastic and mount the toggle switch so that you can flip it from the outside.

  PHOTOS USED BY PERMISSION OF CARL HILL-POPPER

  Commercial Hardware and Techniques

  What goes on behind those two-way swinging doors leading to the commercial kitchen? More and more restaurants are sharing with the public what they’re doing, even going so far as to blog their thoughts and recipes for all the world to see. Why? Well, for one, it serves as great publicity for the restaurants. And secondly, so much of what’s done in the high-end modernist restaurants requires so much work that it’s probably cheaper for a home chef to go and eat at the restaurant than it would be to try undertaking one of their recipes anytime soon.

  Even if you’re not going to attempt a full 26-course dinner, you can learn a lot by seeing how the pros approach food and the lengths to which they go to in their quest for a truly fantastic and delightful meal.

  Since the techniques in this section are not, in and of themselves, going to put dinner on the table, you might wonder how to work them into your cooking. Think of this section like knife skills for modernist cuisine: a few pointers for what’s happening behind those swinging doors. For inspiration and ideas of what to do with these skills, try turning to the Internet. Here are a few blogs worth checking out (most of these are associated with interviewees in this book as well):

  Cooking Issues (http://cookingissues.com)

  Nils Norén, Dave Arnold, and other members of the French Culinary Institute blog about their investigations into cooking phenomena, giving good explanations of how to use new technologies.

  eGullet.org (http://forums.egullet.org)

  The mother of all forums related to food, eGullet is home to many threads covering almost any topic you can imagine related to the creation of food, including the infamous sous vide thread.

  Ideas in Food (http://blog.ideasinfood.com)

  Alexander Talbot and Aki Kamozawa blog about their work with food, sometimes including insightful recipes and tips.

  Playing with Fire and Water (http://www.playingwithfireandwater.com)

  Linda Anctil’s blog posts give an evocative and creative approach to food.

  In this section, we’ll take a look at a few techniques that are common in commercial restaurants and examine ways that they can be useful to the home chef. This isn’t by any means a complete list. Rather, this should be enough to get you started thinking outside the box (or, harking back to the functional fixedness concept discussed in the opening chapter, getting to see the box in a different way).

  3D Printing and Mold Making

  Many aspects of "playing with your food" are beyond the reach of most commercial restaurants, either because they’re not worth the time or require a geek to do it.

  For a few high-end restaurants, spending the time involved in making custom molds allows them to create innovative and unusual experiences. Working with fabricators, they’ll create custom silicone molds ranging in shapes of everything from vegetables to eggs, using them to mold asparagus puree set with gelling agents or for signature desserts.

  Then there’s the geek side of things. If you happen to have access to a CNC (computer numeric control) printer, such as MakerBot’s Cupcake, try printing your own molds and cookie cutters. Here’s an example, using none other than that famous penguin, Tux. (Tux is the Linux kernel’s official mascot.) You’ll need a cookie cutter, sugar cookie dough, and frosting.

  Create the cookie cutter. This is the hardest part (second hardest, if you’re the type to eat all the cookie dough before getting to the end). Assemble a MakerBot CNC printer and print a Tux cookie cutter, following the STL and G code files at http://www.cookingforgeeks.com/book/cookie-cutter/.

  Bake the cookies. Using the cookie cutter (shown on the left in the photo below), create your Tux cookies and bake. Allow the cookies to cool before frosting.
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br />   Frost. Until MakerBot comes out with a Frostruder that supports multiple colors, you’ll have to do this by hand. Prepare a batch of frosting (see Baking Soda in Chapter 5 for a simple frosting recipe) and divide it into three bowls, putting most of the frosting in the first bowl. Add yellow food coloring to the second bowl; you’ll use this for Tux’s yellow feet and beak. Add red and blue food coloring to the final bowl; when mixed together, this will make an almost-black frosting.

  To frost, take a first pass using the white frosting, covering the entire cookie in a single full layer of white frosting. Using a dinner knife, take a second pass, lightly smearing the yellow frosting for his beak and feet. For the third pass, transfer the black frosting to a plastic sandwich bag, snipping off the corner to make a piping bag, and carefully dot the two eyes and black edge.

  Filtration

  Filtering is a common technique for separating solids from liquids in a slurry. Filtering is usually done to remove the solids—for example, to create a clear broth free of particulate matter or a juice free of pulp. Other times, the solid matter, such as browned butter solids, is the desired item.

  Sizes of common items (top portion) and common filters (bottom portion).

  Besides filtration, which we’ll talk about here, additives can be used to separate out some types of solids. Some manufacturers use isinglass, a collagen derived from fish bladders, in beer and wine making. The isinglass binds with yeast and causes it to precipitate out. (Sorry, vegetarian beer lovers.) And consommé is traditionally clarified using egg whites, which, like isinglass, bind to small particulates and then coagulate into a large mass that’s easily removed. Mechanical filtration, in contrast, has the advantage of being fast and easy.