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.
The Unscientific Re-Test
For several months I was too busy to pursue further legal distillation tests. Then I remembered I had promised to bring my rotovap to the 2010 Star Chefs demonstration, and the following occurred to me:
1. Crap, I don't want to lug my chiller with all the tubes and propylene glycol to Star Chefs.
2. Crap, they never have enough power in the demo rooms and I'll probably blow a circuit running the chiller and the rotovap.
3. They will have a boatload of liquid nitrogen at the event, which I could use to run the cold-finger (they ran out last year so they over-ordered this year).
4. People might like to see a legal distillation demonstration.
Legal it would be.
Legal Distillation at the Star Chefs Demo (for the rest of the demo, see my upcoming post)
I decided my earlier tests were fundamentally flawed. I had been comparing the results of cold-finger distillation to standard condenser distillation by trying to match the yield and proof of the cold-finger product to the standard product. What if that method was biased against the cold-finger?
For the Star Chefs demo I decided to focus only on making a delicious product with the cold-finger. I vacuum-bagged Thai basil and orange peel in ice water to thoroughly saturate the leaves and peels with water.
Experiments I had run with Tony Conigliaro at his bar 69 Colebrook Row in London (where he is allowed to re-distill with alcohol—the lucky cuss), showed that leaves not fully saturated wouldn't give up their flavor as readily. You can't blend the leaves to mingle their flavor with the water, either—blended herbs distilled with water in the rotovap taste brown and swampy. The swamp thing doesn't happen when you blend herbs and liquor. In a side-by-side test, distilled blended mint plus ethanol beat distilled vacuum-saturated mint plus ethanol; distilled blended mint in water was wretched, while distilled vacuum-saturated mint in water just lacked power.
I loaded the saturated peels and Thai basil in the rotovap, sucked a vacuum, filled the condenser with liquid nitrogen, lowered the distillation flask into the water bath, and commenced distillation. I left Nastassia to finish the process while we went on with the rest of the demo. When she felt she'd pulled off all the water she could, we melted the ice off the condenser with the 200-proof and tasted. It was fantastic. Really fantastic. Nastassia claims it was good because the rotovap required a woman's touch. I'm not so sure because she says that about everything.
The outcome of the demo left me very, very optimistic about the future of legal rotovapping.
Tips and Comments on Running the Cold Finger:
1. Running a cold finger isn't the same as running a standard condenser. Do not add coolant to the cold finger until you have established a partial vacuum in the system. If you ignore this warning you risk clogging the vacuum intake of the condenser with ice crystals—a pain in the rear.
Watch out for condensation here.
2. It's normal for the ice at the bottom of the cold finger to melt under heavy distillation, even with something as cold as liquid nitrogen as your coolant. Condensing water requires a lot of power.
3. A mixture of dry ice and 200-proof ethanol is food-grade and will probably work as well as liquid nitrogen. Dry ice isn't as cold as, but has much more cooling power than, an equal amount of liquid nitrogen. Dry ice is also easier for most people to source. Unlike me—I have liquid nitrogen dribbling out my ears.
Even though liquid nitrogen is super-cold, you will see liquid water at the bottom of the condenser and in the receiver flask. This is normal.
4. As a corollary to 3, you will need a lot more liquid nitrogen than you think. It will take many, many liters to condense 1 liter of product. Keep adding liquid nitrogen throughout the distillation (it runs out quickly). Don't be alarmed, but you will get a huge vapor plume once the distillation starts in earnest.
5. Make sure to melt the distillate off the condenser immediately with 200-proof ethanol. I have no scientific proof, but every distillate I have made with water loses its aroma very quickly. I feel melting it with liquor helps fix the flavor, but I'm willing to be proven wrong.
6. It is extremely difficult to determine how much product you have distilled off your mixture in a cold finger condenser. Some protocol has to be devised to figure this out or recipes won't be repeatable (suggestions anyone?).
Up for Comment:
My old theory as to why liquor-based distillation is inherently better than water-based was threefold:
1. Flavor is captured better in distillations that go through a range of boiling points with large amounts of distillate produced all the time—the way an ethanol-water system works. The range of boiling points in a water-based distillation is much lower, plus many of the more volatile compounds that boil at significantly lower temperatures than water will be boiled off unnoticed in a water-based distillation.
2. Ethanol and ethanol-water mixtures are inherently better at carrying volatile aromas and flavors than water alone.
3. Once distilled, ethanol mixtures hold volatile flavors better.
How do these theories jibe with the new water-based distillations?
First, I am willing to be challenged on all of these theoretical points, as they were arrived at through experience, not scientifically.
If my theories are correct, point 1 is partially addressed in the legal method, because the traces of flavor that get lost in a water-based distillation in a standard condenser freeze on the side of the cold finger and would then be dissolved in straight alcohol at the end of the distillation run, which solves the problem from theory 3.
As to the first part of theory 1 (that a range of boiling points in a distillation leads to better flavor) and theory 2 (that ethanol is a better flavor carrier than water), I guess it's open for discussion. In fact, I haven't been able to devise a good side-by-side test where legal distillation was as good as illegal, so maybe these theories are correct, and illegal distillation is inherently superior. The success I had at Star Chefs, however, leads me to think my theories should be revised.
This post also appears on CookingIssues.com. All photos courtesy of Cooking Issues.