Editor's note: Cooking Issues, the French Culinary Institute blog that Dave Arnold runs with Nils Norén, is perhaps America's most influential blog devoted to the high-tech cooking techniques used in "molecular gastronomy." This post is the first in an ongoing collaboration between Cooking Issues and The Atlantic's Food Channel.
For years I have been distilling illegally in my rotary evaporator because the products are delicious. I don't feel bad about being a scofflaw—our distillation laws are preposterous.
Distillation is defined in the United States as any process that separates ethanol from an ethanol-containing mixture. Unless you are licensed, distillation is illegal. There are no exceptions for personal consumption; adding botanicals to high-proof alcohol and re-distilling it for flavor (to make gin, for example) is verboten, even if you don't raise the proof of the liquor. So most home distillers remain underground and won't talk about their craft for fear of the government knocking on their door, and bartenders are unable to serve house-made distillates for fear of losing their liquor license.
The rotary evaporator, described in my primer here, is an amazing piece of equipment that makes some of the cleanest, purest, brightest-tasting liquors I have ever tasted. Unfortunately, the handful of U.S. chefs that have them in their restaurants in the U.S. only distill water-based products for fear of the aforementioned laws—a horrible pity. Once you have used the rotovap for liquor, water-based distillates are a disappointment. They smell nice, but they taste like lightly flavored water—nothing like the kick-in-the-teeth flavor punch you get from ethanol distillates. I have always been disappointed by water based distillations—until now.
Rotovap setup with a standard tube condenser running propylene glycol.
It's the Condenser, Stupid!
To distill, you must first boil something and then re-condense it back into a liquid. The job of chilling a vapor and turning it back into a liquid is done by a device aptly named the condenser. In a rotary evaporator you have two basic condenser choices—standard cooling tube and cold finger. Standard condensers have a long length of tightly coiled tube on the inside, through which you pump coolant. The large surface area of the coiled tube coupled with the constant flow of fresh coolant makes for efficient condensing. For maximum flavor retention, you want this coolant to be as cold as possible without freezing your distillate to the coils. In practice, it is hard for me to get condenser temperatures below -20 C. You don't want your distillate to freeze because then you don't know how much distillate you have produced (it is difficult to judge from the rotating flask) and if, like me, you have installed a pump that lets you taste your product as you make it, you can't taste. The standard condenser is what most everyone uses. It works great with liquor.
The cold finger condenser doesn't have circulating coolant or coiled tubes. It has an internal sleeve that you fill with something cold—dry ice and acetone, for example, or liquid nitrogen. Because they are filled with super-cold fluid, cold-finger condensers run much, much colder than standard condensers do. You should be able to run them at the same temperature as regular condensers by filling them with ice, salt, and water; this technique sucks so don't bother trying it.
I've had a cold finger condenser for years but it didn't fit my old rotovap. I never bothered adapting it to that machine because I didn't like the idea of freezing my distillate. But my cold finger is compatible with my new rotovap. Experiment time.
Cold finger condenser setup.
I started by using one of my standard liquor recipes but distilling it with the cold-finger filled with liquid nitrogen (about -200 C) instead of my tube condenser at -20 C. The results were good, but I didn't think they were better than normal. (To be fair, I didn't taste side-by-side; more on that later.) I chocked that up to a victory for tube condensers. During distillation, I noticed that a thin layer of frost formed on the cold-finger almost immediately, even before the distillation proper started. Then I thought—hey, what if I ran water-based flavors through this thing? Maybe the super-cold condenser would capture flavors that are lost in water-based distillations made with a standard condenser? The immediate formation of frost, and its implied condensation and capture of flavorful vapor, was encouraging.
If I could get water based distillation to work it would be LEGAL!
Illegal Distilling vs. Legal Distilling: Chocolate Vodka Side-by-Side Test
I made some 120-proof Smirnoff vodka (by illegally re-distilling 80-proof Smirnoff) in a regular condenser. I then added equal amounts of cocoa powder to one liter of 80-proof Smirnoff and 600 milliliters of water (the amount of water in the bottle of Smirnoff). I then distilled the vodka/cocoa mixture in the regular condenser and the water/cocoa mixture in the cold-finger. I tried to judge the amount I had distilled by looking at the remaining liquid level in my distillation flask—a difficult task. My aim was to distill 600 milliliters from the liter of vodka and add enough water to make a liter of 80-proof, and distill a little under 400 milliliters from the water-based cocoa, then melt the distillate off the condenser using the high-proof Smirnoff to make a liter of 80-proof.
Frost builds immediately in the condenser.
In a side-by-side, the illegal chocolate beat the legal one hands down—but there was still hope for the legal method. It was good. It was oodles better than any other legal distillate I'd ever made. I decided the Smirnoff was no good for these tests; I needed something higher-proof. I didn't want to use the 195-proof stuff you can get in the liquor store. It is horrendous—you'd rather suck on an isopropyl alcohol prep swab. Instead I looked online at Spectrum, the chemical supply house. It just so happened that they were running a special on 200-proof pure, anhydrous (no water), USP (food grade) ethanol (booze). They were selling it for only 16 dollars a liter—the equivalent of $6.40 a liter for 80-proof. I ordered some and tasted it. It was primo! I immediately ordered 16 gallons (a day later the price went back to normal—triple what I paid).
I re-ran the experiment with the super-hooch. This time, my alcohol-based distillation consisted of cocoa powder plus 200-proof and water in the standard condenser, versus straight water and cocoa in the cold-finger. Again I melted the water-based distillate off the condenser with booze, this time 200-proof. When I corrected both distillates for proof, the illegal chocolate still won—but not by as wide a margin. Legal was getting better, but still not up to par.
NEXT: The final verdict on legal, water-based distilling