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[10/7, I’m not ready to release a product yet, but my prototypes keep exceeding my expectations. I’m about to get a few out there for others to test.]
I am about to offer an American made, well tested Clevenger apparatus for gin distillers. A lot of the extra information here is to keep me happy and prove I did my homework.
[Notice the glass rod to prevent bumping. I did not know that trick. I use pumice stones and have seen silicon carbide used in old books.]
For quite a few years I have been exploring botanical analysis for gin production & other aromatized products. A device that has always intrigued me is the Clevenger apparatus for measuring essential oil via steam distillation which was invented in 1928. This test is particularly important because botanicals can fluctuate significantly in oil content. Operation is quite simple; botanicals are boiled in a flask with water. Vapor ascends, condenses via a cold finger, runs into a graduated section where oil separates from the water then the water gradually fills a return tube and runs back to the boiling flask to redistill (often called cohobation). So you’ve got a loop with a section where the oil separates, but getting a useful measurement becomes a little trickier than that.
Gin distillers picked this up and Herman Willkie used it at Hiram Walker as described in Controlling Gin Flavor, 1937, which is still the most important work on gin production ever written. Clevenger data was used to show the degradation and loss of essential oil over prolonged storage of botanicals. It was also used to scale the botanical charge for production consistency which is an industry standard for all mass market gins, but not currently practiced at the craft level.
We see even more Clevenger use from Willkie representing Seagram in 1940 via a seldom seen text (that strategically makes no mention of gin) aiming to develop domestic interest in growing fine botanicals. The appendix is where botanical analysis for gin is detailed. Seagram’s modification has to do with how the Clevengers are ganged side by side to run in a hot wax bath, avoiding condensation, and how the condensers are setup.
Willkie also details his protocol for essential oil measurement via Soxhlet extraction with organic solvents which I’ve explored, but it is not viable for the distillery with anything less than strong national distribution. Clevenger analysis takes five minutes of active time to setup and possibly five more minutes to measure the result. It can run for a few hours unattended with a timer to shut it off. Soxhlet extraction requires more skilled active time and then a lot of accessories on top of the glassware (analytical balance) plus organic solvents that are hard to source (hexane, dichloromethane). A Clevenger apparatus may cost $300 while Soxhlet determination may require no less than $3000 and then even more if you need compliance for disposing of the organic solvents. The point is the Clevenger is the only practical tool for small scale gin producers.
The state of the art for standardizing a botanical charge may be $30,000 pressurized solvent extraction that can handle an entire carousel of samples. That is just for quantitative essential oil determinations. It is not clear what brands are large enough to use that. You can stack GCMS on top of that and spend even more money.
Backing up a bit to Clevenger’s 1928 paper, they were aware of solvent based essential oil yield determinations, but still pursued the simpler Clevenger apparatus because it allowed the isolated essential oil to be available for other determinations like optical rotation & refractive index which are proxies for qualitative changes. Clevenger was also immediately aware of using his device with a solvent assist like xylene, but acknowledged it was only used when additional analysis was not being preformed. Modern gin distillers will likely always use xylene and never measure optical rotation, refractive index, or specific gravity of the oil. For all qualitative work on botanicals, the birectifier has proven, cheaper, faster, and more insightful.
Xylene is a common organic solvent you can purchase at any hardware store and is a close cousin of Acetone. With a Clevenger, it is used only as a single 1.0 ml. It is less dense than water and insoluble. It floats in the tubing where the essential oil collects. If you do not use xylene, the essential oil often end up as globs that don’t flow together. Xylene dissolves the oil globules creating a cohesive easier to measure mass. Clevenger acknowledged that without xylene, you often you had to take a piece of wire and stir the oil into a cohesive mass, but then you would introduce a degree of error with what stuck to the wire which he allowed as acceptable. Xylene was also commonly kept around for moisture determinations with a Dean-Stark tube.
[Surface tension is really interesting and what I’ve found is that even with xylene, after completion, you may have to hold the Clevenger then rock it back and forth slightly to dislodge water that may be stuck next to the xylene. Without xylene, things can be a nightmare. When you tackle these idiosyncrasies, you can get really repeatable measurements. This is all fairly simple, but important for delegating operating tasks.]
Solvent assistance from Xylene also has the benefit of making all oils less dense than water, meaning one Clevenger design can be used. If you don’t use xylene, botanicals like cinnamon, clove, et. al. require a different design where the return tube is in a different position. This design is only relevant when you want the oil to be pure for other measurements. It is functionally obsolete to the gin distiller.
[Integrated slant in the 1955 design so you don’t have to tilt the device.]
I have owned several different Clevengers and even had one custom made years ago, but have never been satisfied with how they work. That has changed with the 1955 A.O.A.C. design. The 1955 Clevenger builds upon the original by how the legs are positioned and how the condenser is scaled. It also features a large pear shaped reservoir under the oil collection tube to accumulate insoluble emulsion rather than returning it all to the boiling flask.
One other Clevenger design does exist and I have explored it. The glass is elaborate and instead of featuring a cold trap, it features an integrated five bulb Allihn condenser. It then has ports to input xylene and equalize pressure. It features a 3-way stopcock that wholesales for $150 (an American made 2-way is $40). My import version immediately broke at the stopcock. They used a 2-way stopcock and drilled a hole to create a 3-way. I have tried to make this version myself and there are so many extra steps to manufacture. It would cost more than the birectifier to produce as American made and the average import will no doubt break from inferior fittings. At the same time, it does not use any of the optimizations in the 1955 design.
The big design problem solved by the 1955 version is condensing the vapor on one side of the device then rolling that condensate across a slant so it enters the graduated tube will minimal turbulence. Operators of the original design often set theirs up at a slant to achieve the effect somewhat. Integrating the slant, makes it easier to delegate ideal operation (and look purposeful to a tour group!). Minimizing turbulence reduces time to collect the essential oil because less oil is inadvertently returned to the boiling flask. Maintaining the cold trap design also reduces the complexity of having fittings to equalize the pressure. Not using a 3-way stop cock saves a ton of money, but we can elaborate on that.
I systematically tried a lot of stuff to innovate and learned a lot of lessons as well as how the optimizations work. I even tried to replace the cold side of the device with Luer Lock fittings to reduce complexity and use a small syringe body for its graduation. The issue there is that the tubing must be wider than what surface tension can bridge across or the inner diameter hydraulically seals. The tubing must be wide enough that water can slide past the oil without surface tension interference. Otherwise it pushes the oil downwards until it is pushed up the return tube, back to the boiling flask.
The typical Clevenger has collection tube graduated for 4.0 ml printed right on the glass. This is extremely laborious to make and prone to errors. I’m not sure how accurately import Clevengers are graduated. The stopcock is used to lower the oil level until it zeros on the graduation you want, but you often overshoot then have to add more water to raise the oil level and try again. An alternative may be to mechanically attach a moving scale that is simply raised or lowered to zero at the oil meniscus. This would increase accuracy and reduce production complexity. It may also eliminate the need for a stopcock which are expensive and prone to leaking. It would be replaced with a threaded drain plug. Stopcocks comprise multiple pieces which are notorious for being lost when cleaning.
The best method for calculating the oil volume may be to attach collars similar to what is on a graduated cylinder. A caliper would be used to measure the height of the 1.0 ml xylene. After operation, the collars would be moved to measure the xylene plus oil. The difference in height, compared to the 1.0 ml xylene would compute the oil volume and possibly more accurately than any contrived scale. Production would simultaneously be simpler and measurements more accurate.
I have combed every old book for every insight on using Clevengers for essential oil determinations. Seagram’s protocol used 100 grams per botanical, irregardless of expected oil yield. Typically, this was in a 1000 ml boiling flask with 350 ml of water. Other protocols use an a botanical amount proportional to the oil yield so nearly 1.0 ml of oil is collected. In-house experience will guide any particularities. The apparatus is run until the oil level does not increase over 15 minutes which is typically 1.5-2 hours.
Device operation comes with many visual queues but nowhere in the literature are they clearly explained. Some botanicals have emulsion while others do not. It is hard to say what the emulsion is or how it relates to the accuracy of the oil measurement. It may simply be unquantifiable noise and a loose proxy for qualitative differences in the constituents. Sometimes the boiling flask starts to foam. That may be an indication that oil has been exhausted and surface tension within the boiling flask has changed. Sometimes, as with juniper, a film of condensate forms on the surface of the boiling flask then goes away. This is likely poorly volatile terpenes that eventually evaporate and leave the flask. It is not clear if there is value in sampling the emulsion because the entire product is contaminated with xylene. You could run a clean device again without xylene to sample any odd phenomena like emulsions to get qualitative queues (I’d just use the birectifier).
What remains to be done before making a device available is more testing and more production practice to make neater joints. I also need to determine if a stopcock is truly necessary because the graduation will not be printed. A stopcock makes the device much more expensive. A solution may also be adapting a Leur lock stopcock to the threaded drain plug. The price will be near $250 and there may be a cheaper student version available in the beginning while I master the joints. If you know you want one, please send me an email or an Instagram DM. If you have any questions, don’t hesitate to ask.
This device is not the end-all-be-all of this kind of analysis, but is affordable, pragmatic, and effective with a strong history of use in gin production. The 1955 is also clearly the best design to use. There is an extremely low learning curve and it is easy to make the results actionable. The price is a minuscule investment relative to letting inconsistent botanicals threaten product quality. This kind of standardization can also drive confidence and buy-in for scale up. I would not want to invest in expensive equipment while flying blind on process consistency! I would not want to blindly plug in wacky botanicals due to supply chain issues! Essential oil determinations are also the key to making special edition gins that splice in smaller batch, rarer circumstance botanicals of terroir which is an entire creative category not presently explored.
[Stopcocks are expensive and must be high quality or you are wasting your time. Making the volumetric scale slide to zero may render the stopcock unnecessary and make the device cheaper to manufacture. I may just make it an option incase someone has an opinion.]
From a business perspective, once, you set your botanical formula, the Clevenger can allow you to start delegating more of production to junior staff, giving them a paint by numbers process. Many startup gin distillers suffer production starts & stops due to sales fluctuations where botanicals are purchased but not used immediately. Essential oil determination can help scale older botanicals for old yield loss keeping product consistency which is critical to driving future sales.
Another angle to consider is when working with a consultant; what is their deliverable? If they make you one good batch using various pounds of various botanicals per charge, how useful is that if it doesn’t come with deeper analysis for botanicals they used? When you have this information as part of the recipe, you can better troubleshoot production issues.
For brands that need to scale up dramatically to national distribution, essential oil determination helps a distiller take on new purveyors when they have exhausted the supply of others. This was extremely important to Seagram which was scaling to global distribution at a time when botanicals took more leg work to get. Stratospheric scale up & supplier exhaustion lead to tackling qualitative changes to botanicals and there is no more practical tool than the birectifier.
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