Your drink is the result of a battle between chemistry and biology. Lucky for you, chemistry won. That’s why your glass of scotch doesn’t taste like rotten eggs and stinky meat.

Yeasts are hardy creatures. You can set them adrift on the air or plunge them in water. You can dry them up and cool them down. Through it all, they’ll just keep coming back. Sometimes the methods they use to stick around aren’t so nice.

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Adam Rogers explains the many biological quirks of yeast in his fascinating book, Proof: The Science of Booze. Rogers examines the discovery of yeasts, their heavy cultivation, and the way the do and do not cooperate with the people who use them to make liquor. By taking a real look at these organisms as living creatures, instead of just an ingredient, he helps us understand some of the factors that shape the modern drink industry.

One major problem that makers of alcohol have to deal with is the internal workings of the yeast, and the fact that they produce something that no one wants to drink. You might recall hydrogen sulfide if you’ve ever been taken on a tedious field trip to see a geyser. While you sat, with your class, watching the Earth’s wet farts, you were bathed in distinctive rotten-egg smell. That’s hydrogen sulfide. That’s what yeasts make. When their material starts getting nutrient-poor, they make even more. Most of that stays in the yeast, which is why leftover yeast in wine is more than an aesthetic problem. When the yeast breaks up, it spill hydrogen sulfide into the drink.

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And when yeast is deliberately mashed up, in the scotch-making process, the entire thing smells bad and tastes bad. Imagine a drink that smells like sulfur and tastes like a meal of meat, eggs, and vegetables, all of which have gone off. That’s what a lot of tasters got when they got scotch made in a special still constructed from steel, Rogers explained. The sulfur compounds gave the entire thing an awful, ripe taste.

So why does your scotch, your whiskey, your bourbon, taste good? Because generally, brown liquors made in copper stills, and copper is greedy for sulfur. It will suck the sulfur right out of your drink. (Wine makers add copper sulfate crystals to their wines to get rid of the hydrogen sulfide.) Knowing they can’t negate biology — although attempts have been made to create yeasts that don’t make as many sulfur compounds — they turned to chemistry, and chemistry came through for them. So enjoy your drink.

Top Image: Culligan

For more insights into the science of how you get drunk, read Proof: The Science of Booze by Adam Rogers.

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