Why is distillation required for producing certain alcoholic drinks?

NCERT Exemplar · Q26

Q. Why is distillation required for producing certain alcoholic drinks?

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Concept understanding — Microbial Fermentation Foods

Let’s begin with something you already know. Think of a pot of milk left out in warm weather. After a few hours, it turns sour and thickens into curd. That change is not spoilage in the usual sense — it is a controlled transformation caused by tiny living organisms called microbes. This is the heart of microbial fermentation.

Fermentation is a process in which microorganisms — bacteria, yeast, or moulds — break down organic substances (like sugars) in the absence of oxygen, producing energy for themselves and, as a by‑product, substances that change the food. When we deliberately use this process to make food, we call the result microbial fermented foods.

You have eaten many of them without thinking twice: curd (yogurt), idli and dosa batter, bread, cheese, pickles, vinegar, and even the dark chocolate you might enjoy. Each of these relies on specific microbes doing their work.

Note

The NCERT textbook (Class XII, Biology, Chapter 10: Microbes in Human Welfare) introduces fermented foods under the topic “Microbes in Household Products.” It lists curd, cheese, idli, dosa, and bread as common examples. The key point is that these are not modern inventions — they have been part of Indian and global diets for centuries.

Why does this matter? Because fermentation does three things that are valuable for us:

Preserves food — The acids or alcohol produced by microbes prevent spoilage by harmful bacteria. Pickles stay edible for months because of lactic acid from fermentation.
Improves digestibility — Microbes break down complex molecules. Lactose in milk becomes easier to digest in curd; the proteins in soy become more digestible in tempeh.
Enhances flavour and texture — The tang of yogurt, the airy holes in bread, the umami of soy sauce — all come from fermentation.

Let’s look at a few examples from your daily life, as the NCERT would describe them:

Curd (yogurt): Milk is boiled and cooled, then a small amount of previous curd (containing Lactobacillus bacteria) is added. The bacteria convert lactose into lactic acid, which thickens the milk and gives it a sour taste.
Idli and dosa batter: Rice and urad dal are soaked, ground, and left to ferment overnight. Naturally occurring Leuconostoc and other bacteria produce carbon dioxide gas, which makes the batter rise and gives idlis their spongy texture.
Bread: Baker’s yeast (Saccharomyces cerevisiae) ferments the sugars in dough, releasing carbon dioxide that makes the dough rise. The alcohol produced evaporates during baking.
Cheese: Milk is curdled using rennet (an enzyme) or acid, then specific bacteria and moulds are added to ripen it. Different microbes give different cheeses their distinct flavours — for example, Penicillium roqueforti gives blue cheese its veins and sharp taste. …

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Distillation is required to produce alcoholic drinks with a higher alcohol content than what natural fermentation alone can achieve, because fermentation stops when the alcohol level reaches about 15% — distillation concentrates the alcohol by separating it from water and other components.

Fermentation, the natural process by which sugars are converted into alcohol by yeast, has a built-in limit. Yeast cannot survive in an environment where the alcohol concentration exceeds roughly 15 percent. This means that any drink produced solely by fermentation — beer, wine, cider — will have an alcohol content capped at that level. If you want a drink with a higher alcohol percentage, such as whisky, rum, vodka, or brandy, you need a method to concentrate the alcohol that is already present in the fermented liquid.

That method is distillation. Distillation works on a simple principle: alcohol boils at a lower temperature (about 78°C) than water (100°C). When the fermented liquid — called the "wash" or "wine" — is heated carefully in a still, the alcohol vaporises first. This vapour is then collected and cooled in a condenser, turning it back into liquid. The resulting liquid, called the distillate, has a much higher alcohol content, often between 40% and 60% or even higher.

Note

The exact alcohol percentage of the final drink depends on how many times the liquid is distilled and whether the distiller keeps only the "heart" of the distillate, discarding the first and last parts (the "heads" and "tails") which contain unwanted compounds.

Distillation does more than just raise the alcohol level. It also allows the producer to control the flavour of the final drink. During distillation, various flavour compounds — called congeners — are separated based on their boiling points. Some of these compounds contribute pleasant aromas and tastes, while others can be harsh or even toxic. By carefully managing the temperature and the cut points, a skilled distiller can create a spirit with a clean, smooth character or one with a rich, complex flavour profile. …

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Q.Why is distillation required for producing certain alcoholic drinks?

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