The Basics of Distillation; Part 3

You’ll probably hear some unfamiliar terms in discussing the actual process of distillation. These terms appear in distilling brandy and whisky; I don’t know about white spirits like Vodka and Gin. One term is: Low wines. What does wine have to do with whisky? My theory is that this term probably came from some of the first applications of [double] distillation: Making brandy, which is distilled wine. So what’s low about it? Well, I suspect that the “low” comes from the fact that the ABV isn’t high enough yet, meaning the low wines have to be further distilled.

What about these: Foreshots? Heads? Middle cut? Feints? Tails? A “cut” is when the output of a pot still changes from undesirable to desirable (or vice versa). When the cut is made, the liquid output from the still is literally redirected to a different receiver (container). “Heads” (also known as “foreshots”) precede the “middle cut,” which precedes the “tails” (also known as “feints”). The “heads” or “foreshots” can contain unsafe or unpalatable chemicals. The “middle cut” is the desired output of the pot still. The “tails” or “feints” are what comes out of the still after sufficient alcohol has been extracted from the still such that the concentration in the output is no longer high enough.

We already know that the distillation process for Scotch takes at least two passes. The first pass is performed by the wash still, which takes the beery contents of the washback and concentrates the alcohol content to create the “low wines,” the output of the first step of distillation. The low wines are the middle cut of the wash still. According to this description, the foreshots off the wash still are discarded into animal feed. I have heard that a stillman (the person who operates the still; sorry for the politically incorrect term!) can tell by smell when the “middle cut” begins. The resulting low wines are 15-20% ABV, about double the alcohol concentration of the wash. Here are two additional descriptions of the distillation process, with decent diagrams.

It’s useful to step back and remember what’s happening here. The big picture is that distillation is a process of taking a liquid mixture that contains lots of chemicals with different boiling points, boiling the lot of them, and controlling the condensation process. The more volatile liquids will boil sooner than the less volatile liquids, so they can be preferentially captured since they will condense sooner. The pot still is not a continuous process. It is filled (the official term is: charged), and heated until virtually empty, then charged again for the next batch. (There are other types of stills that operate continuously, but they are not used in the production of Single-Malt Scotch Whisky. You’ll find them in petroleum distillation, Single-Grain Scotch Whisky distillation, and many other chemical engineering applications.)

The second step in the distillation process is another pot still known as the spirit still. The spirit still’s foreshots may be recycled into the wash still for the next pass. For most Scotch whisky, the middle cut is the final output: New make spirit. As with any pot still, the feints are too weak and are captured and recycled into earlier stages of the process. After the second distillation, the ABV is 65-70%, which strongly depends on the alcohol content of the low wines, which in turn strongly depended on the alcohol concentration of the wash.

Lowland Scotch Whisky and Irish Whiskey is distilled a third time, through a second spirit safe. The resulting new make spirit might be around 80% ABV. Since the spirit used to charge the second spirit still is already fairly concentrated in terms of ABV, this additional step doesn’t increase the ABV as much as the pass through the first spirit still did. Occasionally, Single-Malt Scotch Whisky is distilled a fourth time. Bruichladdich recently did this with their “X4 (Perilous Whisky).” The final ABV of that product was 90%…you can see that each step is giving diminishing returns in terms of ABV. On the other hand, there was enough Ethanol in this product to run a Formula 1 racing car.

Aside on ABV: A higher ABV has an interesting effect. Because alcohol’s boiling point is less than human body temperature, when a high-ABV whisky hits the tongue the alcohol “flashes” — it evaporates very quickly. This carries aromas to the nose that may not be obvious before you taste. Keep in mind that the ABV of the final bottled product is less than the ABV of the new make spirit that goes into the spirit safe because the aging process reduces the ABV by up to 3% per year in Scotland, depending on seasonal humidity and temperature variations.


1 Comment»

[…] also find this improves the flavor of the final product, particularly if the tails are recycled (a common practice at Scotch […]

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