Distillation of Scotch

04 Dec

We know that the process starts with barley, which is malted and dried over heat, perhaps from burning peat, perhaps not. The dried malted barley is then pulverized to expose the complex carbohydrates and enzymes in the center of the barley. The barley plant uses similar cell metabolism used by other plants and by people. In short, the energy to drive the processes within the cell come from simple sugars.

The preferred food of brewer’s yeast is also simple sugars, like Glucose. After all, brewer’s yeast is as much a life form as a barley plant or a cow. Or you. At the cellular level, we need Glucose for energy. But glucose is hard to store. Glucose can be converted into complex carbohydrates which are easier to store…or into fats which store even more energy but which require more complex chemistry to convert sugars to and from fats.

Plants mostly don’t use fats (they lack organs like livers that are good at manipulating fat molecules, and they lack fat cells that are good at storing fat). I say mostly because some fruits (avocado for one) are rich in simple fats. Glucose makes the yeast happy but only after the Glucose can be freed from its captivity within the starches. But even the plants, fungus (yeast) and animals on this planet can’t directly consume starch molecules. The enzymes are special molecules that can help do specialized tasks, among them breaking apart complex carbohydrates into simple sugar.

The first trick the distillery needs the enzymes to perform for them is to break up those carbs. They do this by mixing the pulverized malted barley with hot water (to speed the chemical reactions needed to create the Glucose). To ensure that all the available Glucose is produced, this might take more than one pass through hot water. The final product is a sweet liquid that is also warm…in short, the perfect environment for yeast: Wee yeasties.

After a few days, the yeast has done enough work and the resulting liquid can be distilled. It’s now running about 7-10% ABV. The still that is used is known as a pot still. I’m not sure of the origin of that name, but there are other types of stills: Column or Coffey stills (used in producing Single Grain whisky, and from what I understand, Bourbon and Rye), and other types of stills used in chemical applications such as in oil refining. The principle is the same, even if the process is much stinkier.

The liquid that is distilled is like a beer in many ways, and the contents are not a pure “beer” product that you might find in a bottle of your favorite cold beverage. So because the still operates by heating liquids, and because the solids would sink to the bottom, the still has integrated agitators (like a washing machine).

Now, in my first article on distilling, I was mainly focused on purification, and in the case of water distillation that’s the whole point. In the case of Scotch, we really like the impurities. Pure alcohol would taste like…Vodka. In other words, not much flavor. (Note: I am not a fan of Vodka. YMMV.) So what the Scotch producer wants is a way to increase the ABV, and retain those flavorful compounds that we like, some of which may be alcohol-soluble and which may be relatively easy to collect with the alcohol. The bad news is that there are some fairly toxic by-products of the distillation process. Things like fusel oils (a misnomer…they are very volatile alcohol-like chemicals) and other nasty chemicals can be in the mix. If your whisky smells like bananas, don’t drink it — that’s a hint that fusel oils are present.

So the distillers run two passes through two different stills, and this article is long enough now that I’ll go over the actual mechanics of the two passes (or three, or four) when I return to this topic in the near future.

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Posted by on 4-December-2008 in Whisky2.0


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