by Dave Arnold
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 (like gin) 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.
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.
I started by using one of my standard liquor recipes but distilling 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 in 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!
Chocolate Vodka Side By Side:
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 1 liter of 80 proof Smirnoff and 600 ml 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 mls from the liter of vodka and add enough water to make a liter of 80 proof, and distill a little under 400 mls from the water based cocoa, then melt the distillate off the condenser using the high-proof Smirnoff to make a liter of 80 proof.
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 percent 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 + ethanol beat distilled vacuum saturated mint + 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 to distill. 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.
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.
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 LN 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 not arrived at through experience, not scientifically.
If my theories are correct, point 1 is partially addressed in the legal method, because the trace amounts 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.
OK, as a regular reader with a Ph.D. in chemistry I will warn you to be very careful when using liquid N2 for the condenser. I am not sure how likely it would be in this situation, but you run the risk of condensing liquid oxygen. This is just a warning, but liquid oxygen is NASTY, REACTIVE stuff that likes to go BOOM.
Ben
True nuff. Hopefully, we won’t get much liquid O2 in the condenser itself because of the oxygen poor environment, but who knows what happens on the surface up top.
The typical conditions where liquid O2 will collect in a lab setting involve a vacuum distillation, where there is a leak (even a very small leak). The liquid O2 will condense out if the atmospheric air. That being said you do have a couple of things acting in your favor. As the frozen alcohol adheres to the condenser I suspect that would raise the temperature of the surface above the temperature where where liquid oxygen condenses. The other aspect of your setup that which should retard liquid O2 is that you to not keep your collecting flask sitting in liquid N2. While I do think the risk is low, the operator of the rotovape should be aware of the possibility of liquid O2 collecting.
could you approximate these results with a freeze dryer and melting the condensate collected?
Dunno Alex,
You’ll have to try it and tell us!
I was always under the impression that 200 proof alcohol was made by distillation with benzene (water-ethanol forms a low-boiling azeotrope at 190 proof but water-ethanol-benzene forms a high-boiling azeotrope that allows you to distill off pure ethanol before the remaining water turns to vapor). It was always represented to me that there is residual (ppm level) benzene that made 200 proof alcohol unsuitable for consumption.
Or am I wrong, and USP grade anhydrous is made using another method to remove the rest of the water?
Howdy Nathan,
USP is indeed safe for consumption, but I don’t know how they get rid of the last 5% water.
Nathan is indeed correct. 200 proof uses benzene or other human-unsuitable entrainers most of the time. Maybe they’ve got away from using them in the last 15 years, but I’d suspect not; it’d be enough to give me serious pause for concern…
Howdy 2Yaks,
In retrospect, I should have used the 95%. I have been assuming that the USP grade, being rated for consumption, should be pure and free from benzene. I have spoken to two organic chemists, one of whom is worried, because although it is OK to consume in small quantities, the 200 proof might have too much benzene to consume in large quantities, whereas the other chemist used to drink it himself. They have offered to put sume through a GC mass spec to test it.
Does using your NO2 infusion with water give a better result than putting it in the vacuum or is it the other way around?
Dunno Brian, I haven’t done enough water based N2O infusions.
You have no idea how much I cringe to see a massive bottle of laboratory solvent put into lab equipment to make things that someone would consume. Logically, I know it’s all safe stuff but my instincts are screaming that even thinking about lab chemicals and equipment without a fume hood, gloves and glasses will give you cancer. Then make you explode.
Another great article. Although every time you bring up American distillation laws I recall you saying that New Zealand laws allow alcohol distillation. It makes me happy to know that I could, even though I don’t.
I have the same reaction, having spent most of my life in labs. Standards are so different in and out of a lab. Lab safety is, if anything, over-emphasized now, with requirements like annually reporting how much NaCl you have on the shelf, and whether it is in plastic, clear glass, or brown glass containers. Then you go into Home Depot and see a four foot-high stack of gallon jugs of muriatic acid, with no barrier to prevent a kid or cart from running into it.
The only way I can think of to know how much you’ve distilled is to weigh your distillation flask. You would have to break vacuum, detach the distillation flask, and weigh it to reach some predetermined target weight. This would be a bother, but eventually you’d have an approximate time. I also recommend dry ice-ethanol instead of liq. nitrogen.
Yeah I know, I just don’t have dry ice laying around. I used to have a dry ice generator, but it broke.
Theory #3 seems pretty plausible to me, at least for why water distillates retain flavor poorly. Most flavor compounds are fairly to highly hydrophobic, so they will volatilize out of water much faster than pure ethanol or ethanol/water.
It seems to be that a good test of water vs ethanol distillation (at least to validate #2) would be to try something where the flavor is highly oil-based. Orange rinds, cinnamon, hot peppers (well, the flavor is water-based, but the spice is oil-based). It seems to me that the results of ethanol vs water would be very different. If this is the case, then one could figure out what ingredients would work well in water vs ethanol.
Great post (as usual….)
the swamp phenomenon with blended leaves got me thinking. Maybe it is some oxidation process going on. You could try a frew things to prevent that:
Degas you water on the rotavap by repetedly pulling vac and venting with N2 to get O2 out of the water. (Alternatively you can bubble N2 thru water for a couple of minutes, same effect.)
Do the blending under inert atmosphere (add some liq. N2 in there and you have it….
Add some antioxidant pre blending like ascorbic acid, which will not distill over so it would not affect the product.
BTW did you ever try the simethicone idea against foaming in the flask?
Howdy,
I haven’t had a chance to try it yet. Just use the anti-gas stuff from the pharmacy, right?
that´s what I´d try first…..
Also the browning might be enzymatic so blanching might help (but might compromise the fresh flavours). Excellent work as usual, you inspired me to do a Food Science Masters partly so I have a slim chance to get paid to do things like this!
Thank you for the compliment. I’m honored.
An interesting experiment to try with your distillations (particularly the illegal ones) would be to use sequential traps between your vacuum and rotovap–say salt/ice water in the coldfinger, dry ice/IPA (or acetone), then liquid N2. Or just three sequential lN2 traps. Lots of interesting variables here since the volatiles would gradually migrate from the first trap to the last.
Also, Dan makes a good point about liquid oxygen around all those organics. Using an additional lN2 trap would probably be even more dangerous, since there would be less stuff around to keep the temperatures up. Might want to use a blast shield and if you see blue, step away.
Howdy Isaac, I did an event outside the school last night, so I ordered dry ice cause it is easier to ship around than LN2. Distillate tasted fine. I don’t use IPA or acetone cause they aren’t food grade and I don’t want to worry about contamination. I use dehydrated EtOH USP.
One last comment–if you want to use liquid nitrogen instead of dry ice, but want better temperature control, blend the liquid nitrogen with solvent until it gets slushy. The temperature of the slush depends on the solvent you use. You have to keep adding nitrogen as your slush melts, but you have to do this anyway. There are charts out there for this temperature for any solvent you’d like to use. Plus it would solve any liquid oxygen problem.
Or you could fix your dry ice generator.
Watch out for the 200 proof ethanol (which you incorrectly labeled “200 percent pure”). DO NOT DRINK IT!
Alcohol will only naturally distill to 190 proof (95% alcohol). To remove the remaining water to make 200 proof alcohol, benzene is added, and the benzene/alcohol mixture is then distilled to make 200 proof anhydrous. The stuff that you bought has very minute traces of benzene in it. I personally would not drink it. Rather, I’d use laboratory grade 190 proof which is ethanol and water and nothing else. The USP designation is meaningless with respect to the traces of benzene.
Howdy VMS,
I am aware of the benzene issue. I’m going to have mine tested.
I forgot to mention that there is a molecular sieve method for producing 200 proof ethanol from 190 proof that is completely safe, but you have to trace the 200 proof product to be 100% sure which way it was made.
In regards to distillation volume if you can’t easily monitor the mass or volume of the solution in the container that it’s being vaporized in I would try to control the factors that control the rate of vaporization. These would be volume of solution, surface area of vaporization, heat flow into the solution, and pressure of the system. If the condensor can maintain a constant temperature then you should be able to get at least an approximate idea of how much distillate you have made after a given time. As an example vaporizing 500 mL of mint water at 90 deg. C for 20 min with 100 cm squared surface area at one atmosphere should give about the same amount of distillate each time. In theory with some experimentation you could make a reference chart for how long it takes to distill a certain volume if you hold the other parameters constant. In practice I’m not sure how sensitive it would be to things like altitude, ambient humidity, and starting temperatures of the solution and still components. It could be more trouble than it’s worth to control all the variables well enough to have a predictable volume of distillate. It might be worth a try if you’re really keen on replicable results.
Dave,
Brilliant work! I would like to echo part of Jake’s comment above. Flavour molecules are often poorly water soluble and therefore distill much better when ethanol is present. For separation by distillation not only boiling points but also interactions between the compounds distilled are important. Ethanol can act as a “carrier” for flavour compounds.
There is a reason why flavour distillates are often made with ethanol… So, IMHO 2 is correct.
Like all scientist above, I was scared by your use of the 100% ethanol, we always order the 96% food grade for drinks with Christmas.
In the future I’ll order the lower proof –just to be safe.
Dave,
You make the following statement, “For maximum flavor retention, you want this coolant to be as cold as possible without freezing your distillate to the coils.” however is this true? I always thought that it was only important to get down to around the serving temperature, say somewhere in the mid 50sF. By not getting colder am I really losing something? I believe that in Cognac and Armagnac production, tap/well water is used as the coolant.
thanks
Howdy Mait,
In traditional distillation what you say is correct, because ethanol is the desired product with very few congeners desired. We want to capture essentially all of the congeners, so we try to get a very high temperature delta which lets us do a fast distillation without losing much.
Hi Dave,
I was rotovapping in lab thinking about this problem today, and I remembered a sidenote from an earlier post that faster distillations gave better flavor than slow distillations – is it possible that the water distillations are just too slow because of the higher boiling point/lower vacuum required?
Also in terms of retaining flavor would it be legal to add ethanol to your trap? you’d have to keep the trap cold (ice bath?) so it wouldn’t evaporate too much but that might retain some of the flavor better than the water.
Hello Allie,
I think part of the problem is as you state it, but there is something else as well. The aroma and flavor of water based distillates are extremely fugitive (compared to ethanol distillates). I think water is just poor at holding on to the flavors, so it is easy for them to get pumped out through the vacuum system. I don’t see a legal problem with adding ethanol to the trap because it is never subjected to a separation process –so it isn’t ever distilled.
For legal flavor extraction I’d think the way to go is heating a water-based solution under reflux, bubble some nitrogen through it, and connect the top of the condenser to a trap/bubbler and fill it with ethanol, so the off-gas from the top of the condenser bubbles through the ethanol. Put the trap in dry ice, and the combination of the ethanol solvent, and the low temperature should trap the volatiles in the trap. Since the solvent (water) is mostly not getting past the condenser, you can run the thing a long time w/o having to muck with the trap.
Oh, yeah, if you take 190 proof alcohol, and pass it over dry lime (CaO) as a dessicant, you should be able to get 199 proof alcohol.
We aren’t sure if our dehydrated alcohol has any benzene in it. It is USP, so I hope not.
P.S. The alcohol in the “thumper” is what catches most of the flavors that you would want.