Yeast is what makes essentially all alcohol. Beer, wine, whisky, vodka/gin, sake, tequila, etc., all get their kick courtesy of the humble yeast: A single-celled organism that is classified as a fungus. Seriously! The edible (well, drinkable) kind of alcohol is Ethanol (C2H6O). If you are a chemistry or biology geek, you will recognize that Ethanol plus water (in the correct ratio) can be converted into sugar through some cellular magic that combines some water with some Ethanol and yields Glucose (chemically: C6H12O6). The latter can then be readily converted to energy in the body, which is why alcohol has calories.
Yes, Ethanol is readily converted into sugar (Glucose), but the body loses water in the process, which happens in the liver. The water the liver needs to metabolize alcohol is pulled from the bloodstream, which is why hangovers are often associated with a dry mouth. One way to prevent this is to drink lots of water before bed. Aspirin also is rumored to work. The fact that the liver is the first stage in alcohol metabolism is why the liver is affected (adversely) by excessive, prolonged alcohol consumption. But never fear, alcohol (Ethanol) is produced naturally in the body and one of the liver’s many functions is to be able to metabolize alcohol, a need that far pre-dated the discovery of fermentation and distillation!
All of this because a lowly fungus is adept at converting sugar or other simple carbohydrates into Ethanol. I can’t find any examples of Ethanol being produced naturally, except via the action of yeast. And that’s the source of all the alcohol that most people (and many animals) love to consume. All the various forms of alcohol, be they beer, wine, distilled spirits, involve Ethanol production in which yeast acts on a solution of carbohydrates, typically simpler ones.
In the case of whisky, the barley contains the complex carbohydrates that would normally fuel its growth into a barley plant, but they are stored deep inside the seed and distillers must trick the barley into exposing them and the enzymes that can break them down into simple sugars. That’s key to the malting process. Another word for this is sprouting, except that normally when a barley seed sprouts it isn’t killed right away with heat from a peat fire. In malting, you need to stop the process at the right time so the plant doesn’t consume too much of the precious carbohydrates. That’s the drying, sometimes over peat, sometimes over coal. Then the dried malted barley is mashed, warm water is added, and eventually yeast is added once the enzymes from the barley have been induced to break down the complex carbohydrates into simple sugars that are palatable to yeast. This action of the yeast on the mash makes a beer-like wort that is allowed to come to about 6-8% ABV over the course of several days. Then this is distilled, which concentrates the alcohol. Multiple distillations may be used to achieve higher concentration of Ethanol per unit volume. Scotch is, IIRC, usually distilled twice and put into barrels at about 70% ABV. Over time, the alcohol escapes and the barrel strength is reduced to no less than the legal minimum of 40% ABV. To be called Scotch, the final product has to be at least 40% ABV.
Sorry for the rambling post, but I thought it would be fun to give credit to the lowly yeast, without which this blog would not exist!