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

by Jeff Potter

  The UK magazine Intelligent Life did a piece on Dave Arnold, including the "stupid extra length" he went to to make a perfect gin and tonic. Dave explains:

  It was called the $10,000 gin and tonic because there was all this equipment and time, and rotary evaporation, and the PSI measured carefully, and clarifying juices, etc. I was redistilling lime essence to create a clear lime juice so that I could add that to my quinine simple syrup and gin and get the water level exactly where I wanted it and carbonate it. The reason you want it clear is because gin and tonic should be clear, and should have enough bubbles, and the right alcohol content. So I was able to break out every single variable and recombine them exactly the way I wanted.

  The idea of the original recipe, Bottle Strength G ’n T, was to produce a gin and tonic shot at bottle strength (80 proof). To do it, we distilled lime juice and gin to capture the fresh volatiles from the juice and increase the proof of the gin. We then added acids back to the distillate to recreate the flavor of the lime juice, along with sugar and quinine, the bitter part of tonic water. Why all this? Adding sugar, acid, etc. lowered the proof of the gin. If we wanted to serve bottle-strength gin and tonic shots, we had to raise the initial proof. Plus, distilling the lime volatiles gave us a perfectly clear drink that carbonates well (pulp is a carbonation killer). We no longer serve this version, because it only tastes good at around 0°F / –18° C. Served any warmer than 5°F / –15° C, and it tastes unbalanced; any colder than –9°F / –23° C, and it is painful going down. It was hard to get people to drink quickly enough, when the shots were at the right temperature.

  This same technique, when watered down to 15–20% alcohol by volume, produces our perfect G ’n T, and it’s much easier to do. I use what we call simple agar clarification on lime juice. I can do it in 20 minutes on a camp stove and I don’t need the high-end equipment to make it. It’s back to a normal cost in terms of equipment, except for a carbonation rig. The good news is that it’s very inexpensive to get a real carbonation rig at home. The whole carbonation rig costs well under $200. A single 20-pound tank of CO2 costs about $20 to refill, and it makes 200 to 400 gallons of seltzer or liquor. Everyone should have one in their house. Everyone.

  Clarified lime juice. Squeeze the juice from 10 limes into a container, running through a sieve to remove pulp. Weigh the juice; it should be around 500g. Set aside.

  In a pan, create an agar gel using water and agar. Measure out a quarter of the amount of lime juice in water, roughly 125g of water, and create a 10% agar gel, around 12g (this will result in a 2.0% concentration once mixed with the lime juice). Once the agar has melted, remove from heat and pour the water-agar mixture into the container with the lime juice and let it rest for half hour or so, until set.

  Once the lime gel has set, use a whisk to break the gel into pieces. Take the whisk and make zigzag slashing cuts; don’t actually whisk the gel.

  Transfer the broken gel to a cheesecloth (real cheesecloth, not the loose mesh stuff) or towel. Fold the cloth up into a ball.

  Hold the balled cloth above a coffee filter and squeeze it with your other hand, massaging it to force out as much liquid as possible. (The coffee filter will catch any small chunks of agar that happen to leak through).

  Simple syrup with quinine. Create a simple syrup (2 parts sugar, 1 part water), then add diluted quinine sulfate. Be careful! Quinine in anything other than minute quantities is poisonous! The legal limit is 83 parts per million of quinine, which is 0.083 grams of quinine sulfate per liter of liquid. You will need considerably less than this. Quinine goes from pleasantly bitter to extraordinarily bitter rather quickly. Make a solution of 1g quinine sulfate in 500 ml of water (or gin) and use no more than 40 ml of this solution per liter of finished product and you will be okay. You will probably like less than half that amount.

  To assemble:

  4 oz gin

  2 oz clarified lime juice

  Simple syrup with quinine to taste

  Salt to taste

  Chill in freezer. Carbonate to 40 PSI.

  Cream Whippers (a.k.a. "iSi Whippers")

  We’re all familiar with whipped cream in a can. A cream whipper is a reusable version of the can, without the cream, that you fill with cream or whatever else you like. They’re a simple yet clever design: pour your contents into the container, screw on the lid, and pressurize using a small, bullet-like cartridge that provides either nitrous oxide or carbon dioxide to the can through a one-way valve.

  Cream whippers take their name from their primary purpose: making whipped cream. With a whipper, you can control the quality of the ingredients and the amount of sugar used. Fill it up, store in the fridge, and there’s no functional difference between a whipper and the more familiar whipped cream in a can.

  The obvious extension is to create flavored whipped cream. Toss some orange zest and maybe a bit of vanilla sugar into a pint of organic cream, and spray away. Try tea-infused cream: steep some Earl Gray in cream and transfer it to the whipper, or go smoky and use Lapsang Souchong. Just remember to strain the tea leaves out before filling the canister of the whipper! You can also spike the cream—make amaretto cream to go on your coffee with 4 parts heavy cream, 2 parts amaretto liqueur, and 1 part powdered sugar.

  But the real fun with cream whippers (besides whipped cream fights) is passing other liquids through them. You can whip any liquid or mixture that has the ability to hold air—that is, anything that can be turned into a foam (sometimes called an espuma in menu speak), including foamed "waters" flavored like carrots or desserts like chocolate mousse. You can even put pancake batter in a cream whipper (hence the whole "pancakes in a can" thing). Because the contents are ejected under pressure, small, pressurized bubbles come along for the ride and expand, leading to mechanical injection of air into the liquid. This is why cream turns into whipped cream, although the foam that’s generated isn’t as stable as manually whisked whipped cream.

  The most common brand of cream whipper used in the food industry is made by iSi (it’s not uncommon to hear a cream whipper simply called an "iSi"). Regardless of manufacturer, basic models run $40 to $60 dollars; cartridges are about $0.50 each in bulk.

  Note

  Don’t use chargers made for BB guns. They aren’t food grade.

  This might be more than you want to spend upfront for just whipped cream, but if you’re a regular user of the canned stuff, the long-term savings alone will make it worthwhile. If you want to play around with textures and flavors in the kitchen, it’s downright cheap.

  Cream whippers also come in a "thermal" style (i.e., built like a Thermos) that’s useful for keeping contents cold if you’re working onsite. The thermal versions can’t be used in water baths, though, making it harder to do hot foams or to partially poach the contents à la sous vide for egg-based custards.

  A few things to keep in mind when working with a whipper:

  Make sure the gasket is properly seated and the threads on the lid are clean when screwing on the lid, unless you want chocolate cake batter, cream, or pancake mix sprayed 10 feet in a random direction.

  Always run your liquid through a strainer (~500 micron is fine) to remove any particulates that might clog the nozzle. You can skip straining things like plain cream, of course.

  When working with heavier batters, you can double-pressurize the canister. After pressurizing with one cartridge, remove it and pressurize with a second one. You’ll find that the pressure decreases as you run through the contents, because the airspace in the whipper increases as the contents are ejected.

  If your liquids fail to foam correctly, try adding some gelatin, which provides structure. If you don’t mind taking a shortcut, try using flavored Jell-O.

  You can also use a whipper as a source of pressure. One technique uses an adaptor from McMaster-Carr to connect the spray nozzle of the whipper to a length of plastic tubing. Fill the tubing with a hot liquid with agar or other gelling agent, let it set, and use the whipper to force-eject the "no
odle."

  Another thing to try is using a CO2 cartridge to create "whipper fizzy fruit"—fruit that has been carbonated, giving it a fizzy texture. Try popping grapes, strawberries, or sliced fruit such as apples and pears into the canister and pressurizing it. Let rest for an hour, depressurize, and remove fruit. Not exactly haute cuisine, but fun to do as a party trick. Fizzy raspberries make a great basis for a mixed drink.

  Chocolate Mousse

  This creates a very light chocolate mousse, almost the complete opposite of the dense chocolate mousse based on agar from Chapter 6 (see Chocolate Panna Cotta).

  Heat to a temperature hot enough to melt chocolate (130°F / 55°C):

  1 cup (250g) heavy cream

  Remove from heat and whisk in to melt:

  6 tablespoons (60g) bittersweet chocolate

  ¼ teaspoon (0.6g) cinnamon

  Transfer to whipper canister and chill. Make sure the liquid is completely cold—fridge temp—before using. Otherwise, the cream won’t whip.

  Pressurize and dispense into serving glasses or on a plate, as desired.

  Notes

  You can dump the canister in a plastic container filled with half ice, half water to chill it quickly.

  The cream really does need to be completely chilled. If it’s not, instead of getting a light, airy chocolate mousse foam, you’ll get a jet of chocolate-flavored heavy cream.

  Foamed Scrambled Eggs

  This egg foam is something like a whipped mayonnaise, but incredibly light. Try it with steak and fries. This recipe is based on a recipe by Alex and Aki of http://www.ideasonfood.com fame.

  Measure out into a bowl:

  4 large (240g) eggs

  5 tablespoons (75g) heavy cream

  ½ teaspoon (2g) salt

  ½ teaspoon (2g) sriracha sauce

  Using an immersion blender, thoroughly purée the ingredients. Strain into a nonthermal whipper and screw lid on, but do not pressurize. Place whipper in a water bath at 158°F / 70°C and cook until the mixture is partially curdled, around 60 to 90 minutes. Remove from bath, check that eggs are just partially set, and pressurize. Dispense into small bowls and garnish, or use as a component in a dish.

  Notes

  Try using the small strainer from a loose-leaf teapot when filtering liquids—it’s easier to hold above the container while pouring in the mixture.

  30-Second Chocolate Cake

  In a microwave-safe bowl, melt:

  4 oz (113g) chocolate (bittersweet preferably)

  Add and thoroughly whisk together:

  4 large (240g) eggs

  6 tablespoons (80g) sugar

  3 tablespoons (25g) flour

  Pass the mixture through a strainer to remove any lumps and to filter out the chalazaes (the little white strands that attach the yolk to the egg white). Transfer to whipper and pressurize.

  Spray mixture into a greased glass, ramekin, or whatever microwave-safe container you will cook it in, leaving at least the top third of the container empty. The first time you do this, I recommend using a clear glass so that you can see the cake rise and fall as it cooks.

  Microwave for 30 seconds or until the foam has set. Flip onto a plate and dust with powdered sugar.

  Powdered sugar is the bacon of the pastry world. It goes well with almost everything and is great for covering up things like tears or holes—in this case, covering up the Nutella filling.

  For better-tasting results, try adding Nutella or Fluff: spray a thin layer of cake batter, drop a spoonful of filling into the center, and then spray more cake batter on top of and around the filling.

  Note

  After cooking, cover in chocolate and do a small loopy white icing thing on the top, and you’ve got something close to commercial cream-filled cupcakes.

  Notes

  Try spraying a thin layer of the batter onto a plate and cooking that. Peel it off the plate, coat the top with a layer of jam or whipped cream, and roll it up to create a log-shaped chocolate treat.

  To be fair, you can do a close approximation without using a whipper. Search online for "microwave chocolate cake." I find that the iSi Whipper version produces a more uniform, spongier cake, though.

  Unbaked: nonwhipped (left) and whipped (right).

  Baked: nonwhipped (left) and whipped (right).

  "Cooking" with Cold: Liquid Nitrogen and Dry Ice

  Common and uncommon cold temperatures.

  Okay, strictly speaking, cooking involves the application of heat, but "cooking" with cold can allow for some novel dishes to be made. And liquid nitrogen and dry ice can be a lot of fun, too!

  If there’s one food-related science demo to rule them all, ice cream made with liquid nitrogen has got to be the hands-down winner. Large billowy clouds, the titillating excitement of danger, evil mad scientist cackles, and it all ends with sugar-infused dairy fat for everyone? Sign me up.

  While the gimmick of liquid nitrogen ice cream never seems to grow old (heck, they were making it over a hundred years ago at the Royal Institution in London), a number of more recent culinary applications are moving liquid nitrogen (LN2, for those in the know) from the "gimmick" category into the "occasionally useful" column.

  Dangers of liquid nitrogen

  But first, a big, long rant about the dangers of liquid nitrogen. Nitrogen, one of the noble gases, is inert and in and of itself harmless. The major risks are burning yourself (frostbite burn—it’s cold!), suffocating yourself (it’s not oxygen), or blowing yourself up (it’s boiling, which can result in pressure buildup). Let’s take each of those in turn:

  It’s cold. Liquid nitrogen boils at –320°F / –196°C. To put that in perspective, it’s further away from room temperature than oil in a deep-fat fryer: seriously cold. Thermal shock and breaking things are very real concerns with liquid nitrogen. Think about what can happen when you’re working with hot oil, and show more respect when working with liquid nitrogen. Pouring 400°F / 200°C oil into a room-temperature glass pan is not a good idea (thermal shock), so avoid pouring liquid nitrogen into a glass pan. Splashes are also a potential problem. A drop of hot oil hitting your eye would definitely not be fun, and the same is true with a drop of liquid nitrogen. Wear closed-toed shoes and eye protection. Gloves, too. While the probability of a splash is low, the error condition isn’t pleasant.

  It’s not oxygen. This means that you can asphyxiate as a result of the oxygen being displaced in a small room. When using it, make sure you’re in a relatively well-ventilated space. Dorm rooms with the door closed = bad; big kitchen space with open windows and good air circulation = okay.

  It’s boiling. When things boil, they like to expand, and when they can’t, the pressure goes up. When the pressure gets high enough, the container fails and turns into a bomb. Don’t ever store liquid nitrogen in a completely sealed container. The container will rupture at some point. Ice plugs can form in narrow-mouthed openings, too, so avoid stuffing things like cotton into the opening.

  "Yeah, yeah," you might be thinking, "thanks, but I’ll be fine."

  Probably. But that’s what most people think until they’re posthumously (post-humorously?) given a Darwin Award. What could possibly go wrong once you get it home? One German chef blew both hands off while attempting to recreate some of Chef Heston Blumenthal’s recipes. And then there’s what happened when someone at Texas A&M removed the pressure-release valve on a large dewar and welded the opening shut. From the accident report:

  The cylinder had been standing at one end of a ~20’ × 40’ laboratory on the second floor of the chemistry building. It was on a tile-covered, 4–6″ thick concrete floor, directly over a reinforced concrete beam. The explosion blew all of the tile off of the floor for a 5’ radius around the tank, turning the tile into quarter-sized pieces of shrapnel that embedded themselves in the walls and doors of the lab... The cylinder came to rest on the third floor leaving a neat 20″ diameter hole in its wake. The entrance door and wall of the lab were blown out into the hallway. All of
the remaining walls of the lab were blown 4 to 8″ off of their foundations. All of the windows, save one that was open, were blown out into the courtyard.

  Do I have your attention? Good. End rant.

  Okay, I promise to be safe. Where do I get some?

  Look for a scientific gas distributor in your area. Some welding supply stores also carry liquid nitrogen.

  You’ll need a dewar—an insulated container designed to handle the extremely cold temperatures. Depending upon the supplier, you may be able to rent one. Dewars come in two types: nonpressurized and pressurized. Nonpressurized dewars are essentially large Thermoses. The pressurized variety has a pressure-release valve, allowing the liquid nitrogen to remain liquid at higher temperatures, increasing the hold time.

  Unless you’re renting dewars and having them delivered to your location, stick with a non-pressurized one. Small quantities of liquid nitrogen in nonpressurized dewars don’t require hazmat licenses or vehicle placarding when properly secured and transported in a private car. It’s still considered hazardous material though, because handled improperly, it can cause death. Transportation falls under "material of trades" and it is your responsibility to understand the regulations. For example, New York State defines anything under 30 liters / 8 gallons as a small quantity. (For details, see https://www.nysdot.gov/divisions/operating/osss/truck/carrier/materials-of-trade.)