The Basics of Distillation; Part 2

There are two key components to the pot still. The part where the liquids and solids are (the beery wort created by the yeast) and the vapors that come off of it. Remember, the contents of the still include proteins, amino acids, enzymes, carbohydrates of varying complexity, phenols, alcohols, dead yeast, acids, and other chemicals, not all of which are water-soluble to the same degree (if at all), and some of which are alcohol-soluble. It’s not a simple Ethanol+Water mixture. The goal of distillation is to separate the good stuff from the bad, in a way that is very repeatable. If you make whisky, you need to do this in such a way that each batch of each of your expressions tastes the same from one batch to the next.

It’s been said that Scotch whisky has been said to have over 800 unique chemical compounds within it that contribute to the flavor. Distillation is the process whereby those chemicals are delivered from the wort to the cask. The point of distillation is to produce a liquid with progressively less water (by volume) and progressively higher alcohol (by volume). The point of distillation of Scotch is not to produce pure Ethanol (grain neutral spirits). Pure Ethanol would taste like Vodka…perhaps even blander than that. Scotch producers (and whisk(e)y producers in general) want to preserve the impurities that give their product its unique tastes and smells.

Modern pot stills use integral steam pipes that indirectly heat the wort from within. A still can hold thousands of liters. The temperature is presumably kept below the boiling point of water, but I don’t know that for a fact. Traditionally, direct heat was applied to the bottom of the pot still, and regardless of the source, the heat causes the alcohol and other vapors to escape into the conical or cylindrical column above the liquid level.

As the liquid is heated, the vapors interact with the copper interior of the still, which is said to influence the flavor (no one is precisely sure what’s going on there). Some of the vapor condenses and interacts with the copper multiple times before the condensate is taken out of the still. Stills have various shapes and the surface area and angles are different, which again is said to produce different flavor profiles in the new make spirit.

At the top, there is a downward-angled tube that carries the condensate to the next step of the process (either the next still, or ultimately the spirit safe). The tube is called the Lyne Arm, and is depicted in this excellent diagram. That carries the vapor with its alcohols and aromatic compounds (some of which is presumably already condensed) to the condenser, where most of the condensate is produced. This article on stills lays out many different designs but uses no definitive language: What seems to be clear is that different shaped stills produce different qualities in the spirits, but it’s also true that the stills are not all using the same input. The scientist in me wonders if anyone has tried using an identical mash formulation into various shaped pot stills to see what the specific chemical difference is due to shape alone. Also I wonder what kind of product would emerge if copper were replaced by stainless steel, or glass, or any other chemically inert material.

Next, in part 3, I’ll get to the final specifics of the process: What is the point of multiple distillations? What happens in the first? The second? The third?


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