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although Iīve been to Kentucky and visited eight different distilleries I do not recall the shape and funktion of the so called doubler. The column (or beer)still is familiar. (By the way that was the first experience to the fact that a column still does not necessarily has to be a less subtle production method than the much adored pot still. Itīs all depending at what level you recieve the destillate.) And Bourbon, I presume, often comes out from the column at about 60 % alc. Am I right? So, my question is , what does the doubler do in the production process, and what does it look like?
Another question I have is if Labrot& Graham still is the only distillery using pot stills? And is the Woodford Reserve now made by that method, or is it still bought in from another distillery?
Thank you, anyone who's answering!
Christina, Stockholm, Sweden
Christina, Thanks for you continued interest in Bourbon and Bourbon manufacture. I will try to take a crack at this one:
Bourbon manufactures use continuous distillation for their primary distillation. As a method, continuous distillation has the advantages of energy efficiency, much greater stripping efficiency (the amount of product left behind in the bottoms), more throuput, less cleanout time, and less footprint. They generally require better control equipment (flow meters, etc) and are less flexible.
To understand how a Bourbon distiller selects his equipment, one must first appreciate that ethanol (drinking alcohol) and water have a special relationship. Most liquid pairs, when placed in a still, will seperate a little based on boiling point. As a general example, take a 50-50 mixture and boil it, and get a 60-40 mixture in the distillate, and a 40-60 mixture in the bottoms, redistill and take another step in seperation. In distillation, these steps are called stages. A pot still provides one stage of seperation. A continuous still has as many stages as it has trays (times an efficiency factor). Back to ethanol - water. The distillation seperation curve is very abnormal for ethanol - water. If you take distillers beer at about 9 percent alcohol by volume, and boil it, the resultant vapor is about 60 percent alcohol (~120 proof). This is quite a large seperation for the first stage. If one condenses this and distills again (ie stage two), the result is around 80 percent alcohol (~160 proof). So as you can see, unlike most liquid pairs, alcohol - water can be seperated a great deal by just two stages.
Most Bourbon distillers are looking for a 'white dog' (distillate) that range from 125 to 143 proof to achieve a balance of purity and flavor componets. To achieve this, they need more than one stage of seperation, but less than two. Here is the dilima, if one adds another stage to the continous still, the distillate would be more akin to vodka than bourbon. So the soulition in the Bourbon industry is to use a continous still for the primary distillation, which is capable of stripping the beer to very low alcohol levels, and then taking the much smaller volume distillate and distilling further to the desired proof in a pot still called a doubler..
Remember that one of the advantages of batch distillation (ie a pot still) is flexibility. So it is a rather straight forward process to continue to boil the first distillate (low wines) to whatever proof of secondary distillate desired (high wines) simply by taking the desired amount of water overhead in the batch. In this way, the distiller can achieve the other 1/2 to 2/3 stage required. Another advantage of the doubler, is that the very light componets (heads) and very heavy (tails) can be discarded easily, a practice that removes some undesireables. (As a side note, if one were to remove the very lights using continuous distillation, it would require at least two continuous distillation columns).
So a doubler is just a small pot still used for the second distillation of the product taken from the continuous still. Some distilleries use a different piece of equipment called a 'thumper' for the second distillation. Which is basically a partial condenser, and is operated in continuous fasion. It is more efficient but less flexible than a doubler.
As for apperiance, I have never seen one in person, but it must look like a small tank or small pot still. Copper or a copper alloy would be preferred as contact with copper is generally felt to be benificial to whiskey (my guess is that the copper catalyzes benificial reactions among the flavor componets.)
I have approached this from the perception of someone in the Chemical industry, so I would welcome additional explinations from those closer to the whiskey industry. I want to thank John Lipman for sharing his experiences and insight on this subject in several conversations earlier this year. Touring a distillation room in on my must do list next time I am in Bourbon country.
Mark A. Mason, El Dorado, Arkansas
Mark gave a very good explanation. All I would add is that, having seen doublers, they are nothing special in terms of their appearance, simply a tank with a lot of pipes running into and out of it. Although it is, in fact, a pot still it does not have the classic appearance of one. Supposedly, the doubler at the Old Crow plant was a traditional copper pot still. I have seen photographs of it, but never saw it in person.
--Chuck Cowdery (http://cowdery.home.netcom.com)
Labrot and Graham is the only Kentucky distillery using pot stills and theirs are modified to run more-or-less continuously. They only have pot stills at that plant, so its products will all be pot distilled, however no whiskey made there is currently on the market. It is still aging. The Woodford Reserve you can buy now was made at the Early Times Distillery in Shivley, Kentucky, a suburb of Louisville. Both L&G and ET are owned by Brown-Forman.
Outside of Kentucky, in California, I believe Fritz Maytag uses pot stills for his Old Portero Rye Whisky.
--Chuck Cowdery (http://cowdery.home.netcom.com)
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