Read Cooking for Geeks: Real Science, Great Hacks, and Good Food Online
Authors: Jeff Potter
Tags: #COOKING / Methods / General
Cooking for Geeks: Real Science, Great Hacks, and Good Food (71 page)
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 (LN
2
, for those in the know) from the “gimmick” category into the “occasionally useful” column.
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 nonpressurized 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
.)
Standard lab safety protocols for driving small quantities of liquid nitrogen around usually state that two people should be in the car and that you should drive with the windows down or at least cracked.
When it comes to working with liquid nitrogen, I find it easiest to work with a small quantity in a metal bowl placed on top of wooden cutting board. Keep your eyes on the container, and avoid placing yourself in a situation where, if the container were to fail, you would find yourself getting splashed.
Don’t sit at a table while working with it. Standing is probably a good general rule to reduce chances of injury. And remember: it’s cold! Placing a noninsulated container such as a metal bowl directly on top of countertops, especially glass ones, is not a good idea.
I once cracked a very nice countertop with an empty but still cold bowl during a demo at a large software company whose name begins with the letter M. I’m
still
sheepishly apologizing for it.
One final tip: when serving guests something straightaway after contact with liquid nitrogen, check the temperature (using an IR thermometer) to make sure the food is warm enough. (As a guideline, standard consumer freezers run around –10°F / –23°C.)
One of the classic “silly things you can do with liquid nitrogen” tricks is to freeze a leaf or a rose and then whack it against something to shatter it. Unlike traditional methods of freezing, liquid nitrogen freezes the water in the plant so quickly that the ice crystals do not have time to aggregate into crystals large enough to pierce the cell walls and destroy the tissue, meaning the leaf or flower won’t wilt when thawed.
In culinary applications, you can use this same property to create “dust” from plant material. Lavender flowers, for example, can be rapidly frozen, crushed with a mortar and pestle (which needs to be chilled in a freezer to keep the frozen plant material from thawing), and then allowed to thaw back out. Some chefs have frozen larger items — beets, for example — causing them to shatter in an organic pattern that couldn’t be obtained with a knife.
The standard formula for LN
2
ice cream goes something like this: cream + flavoring + liquid nitrogen + whisking / mixing = 30-second ice cream.
While you can make ice cream with a small quantity of alcohol using traditional methods, those versions have only a mild flavor brought by the alcohols, which are used more as extracts or flavorings than as actual components of the body. With liquid nitrogen, however, you can make a scoop of ice cream with an entire shot of alcohol. Calories are no longer the biggest problem with this type of ice cream; hangovers are.
As with anything you make with liquid nitrogen that’s served cold, check to make sure that it’s not
too
cold before serving it. An IR thermometer is a handy tool for this. Spot-check your ice cream, and if it’s too cold, let it warm up to normal freezer temperature.
Be sure to take the necessary safety precautions!
In the metal bowl of a stand mixer, mix:
- 1 cup (256g) milk
- 1 cup (240g) heavy cream
- ¾ cup (180g) Goldschläger (cinnamon liqueur)
- ¼ cup (80g) chocolate syrup
- ½ cup (80g) bittersweet chocolate, melted
- 2 tablespoons (25g) sugar
- ½ teaspoon (1g) salt
- ½ teaspoon (1g) cinnamon
Taste the mixture to check the balance (try not to drink it all at this point), and adjust accordingly. Once frozen, the mixture will not taste as strong, so an overly strong mixture is desirable.
Turn your stand mixer on and (carefully! with goggles and gloves!) slowly pour in liquid nitrogen. I find it takes about a 1:1 ratio of mixture to liquid nitrogen to set the ice cream. If you don’t have a stand mixer, you can also do this in a metal bowl and stir with a whisk or wooden spoon.
Note
- To melt the chocolate, microwave the milk and then add the chocolate to the hot milk. Let it rest for a minute, so the chocolate warms up, and then mix to combine. You can nuke the chocolate directly as well, but I find it easier and less likely to burn doing it this way.
Dry ice — solid carbon dioxide — is easier to work with than liquid nitrogen. For one thing, it’s solid, so you don’t need specialized equipment to handle it. A Styrofoam cooler or even a cardboard box is sufficient. And secondly, it’s much more readily available. Just make sure to ask for
food-grade
dry ice!
A few words of warning: like liquid nitrogen, dry ice expands into a much larger volume as it sublimates. Do not store dry ice in a sealed container. Also, dry ice and ethanol form a wet slurry that is
very
dangerous. It’s not cold enough to generate the Leidenfrost effect, the phenomenon where a liquid generates a vapor barrier around a much-hotter item. Dry ice and ethanol can wick through clothing and stick to skin.
Besides sticking a chunk of dry ice in a cup of coffee and pretending not to notice while drinking from it (the chunk will sink to the bottom), what else can you do?
Quick-freeze berries.
Industry lingo for this is
IQF
(individually quick frozen), in which large blast freezers rapidly freeze individual peas, raspberries, and chicken breasts. You can toss some dry ice in a Styrofoam cooler and mix in a roughly equal amount of berries or veggies, wait until the dry ice has sublimated away, and then bag ’em and stick them in the freezer.
Make ice cream.
Works just like liquid nitrogen, only alcoholic flavors probably won’t set quite as nicely. Take your food-grade dry ice, place it between two towels, and give it a few whacks with something like a rubber mallet or the back of a frying pan to create a powder. Whisk the powder into the ice cream base until set.
As with LN
2
ice cream, it’ll take a little less dry ice if you start with a base already at freezing temperatures.
Create “fizzy fruit.”
. Drop some grapes, bananas, strawberries — really, any moist fruit — into a pressure cooker, toss in some dry ice, and slap on the lid. As the dry ice sublimates, the chamber of the pressure cooker will hold the carbon dioxide (and bleed off any over-pressure amount), and the fruit will absorb some CO
2
. Wait 20 to 30 minutes, release the pressure, pop off the lid, and munch away.
If a griddle cooks foods by adding heat, it should follow that an anti-griddle “cooks” foods by removing heat. PolyScience, known by many chefs for its sous vide recirculating units, makes a product that does exactly that: its anti-griddle cools down whatever you put on the griddle surface.
You can make a do-it-yourself version by using dry ice, ethanol, and a sheet of stainless steel. You’ll need a solid chunk of stainless steel (plan on ordering a piece from a distributor such as McMaster-Carr). I have a 6” × 6” / 15 cm × 15 cm slab that normally lives in my freezer; it’s handy for those times when you want to cool down a small item quickly. Here’s how it works:
- Rig up a bed of crushed dry ice. Try using a cookie sheet placed on top of a wooden cutting board. The cookie sheet will hold the dry ice/ethanol slurry, and the cutting board will provide insulation between the extremely cold cookie sheet and your countertop. Alternatively, if you have the lid to a Styrofoam container, using the inside, indented part can serve both purposes.
- Pour a small amount of ethanol onto the bed of crushed dry ice — enough to create a level top. (You can use rubbing alcohol or cheap vodka.) The ethanol will remove any air gap between the pieces of dry ice and the stainless steel griddle, and it won’t cause the dry ice to froth in billowy clouds like water would.
- Plop the square of stainless steel on top of the ethanol-topped dry ice. It should be a complete contact fit, just like a heat sink on top of a CPU.
- Spray or coat the top surface of the stainless steel with a nonstick cooking spray, butter, or oil.
- Drop your food to “cook” on the surface, smoothing it out into a pancake shape if desired. After 10 seconds or so, use a spatula to flip it and set the other side. As a starter, try whipping some cream up in a bowl with a bit of sugar and chocolate syrup. Try using a cream whipper with flavored foams or the chocolate mousse recipe from earlier in this chapter.
PHOTO OF WINDELL AND LENORE USED BY PERMISSION OF SCOTT BEALE, LAUGHING SQUID (HTTP://LAUGHINGSQUID.COM)
Windell Oskay and Lenore Edman blog about DIY and open source hardware projects on their website
(
http://www.evilmadscientist.com
)
and occasionally dive into the food arena with their “Play with your food” posts.
You are unique in the sense that you do some really extreme stuff both in hardware and in food. How much of what you do is happenstance versus planned?
Lenore:
Most of the time we are brainstorming. Any topic is fair game for a project. We may have talked about doing an “Apple” apple pie long, long ago, and then we’re at the cooking store and looking at all of the different round-cornered square pans thinking, “This might work,” or “Oh, wow! This is perfect!”
Windell:
That also brings up one of the most important methods we have for solving problems, which is to put it on a list and wait for a really long time until we think of a solution.
How do you know if a project is going to work?
Lenore:
You try it. The apple pie went through several iterations before we figured out a way to make it aesthetically pleasing.
Windell:
There were a couple of different pie shells. We’re not running a commercial kitchen. It actually takes us time to make a pie shell and let it chill. We don’t have an extra one just sitting ready.
Why do you do these projects?
Lenore:
That’s a good question. Why do you breathe?
Windell:
What else are we supposed to be doing? We like to do cool stuff. We have a chance to, so why not?
Lenore:
It’s rewarding to see other people enjoying our projects, so publishing them is rewarding. And you’ve got to eat, right? So you might as well eat something interesting. You have to wear clothes.
Windell:
So wear something interesting.
If you knew the world were going to end tomorrow, what would you want your last meal to be?
Lenore:
I don’t know... We eat a lot of good food, so it’s not like there’s one thing in particular that I would regret not having eaten.
Windell:
If the world were going to end tomorrow, the last thing I think I would do is sit down and have a nice big comfy meal. It doesn’t really seem like that’s going to happen.
Lenore:
I guess if you knew you couldn’t do anything about it, that might be a fine way to end. Sit down and have a big comfy meal. It seems unlikely, but...
Windell:
Water and hard tack in the bunker.