Sugar + yeast = alcohol + carbon dioxide (CO2) + heat. This formula describes fermentation, the process by which all alcoholic beverages are created. This is how all drinking alcohol, since the beginning of time, was rendered.
Now, you ask, “Why the hell do I need to know that?!” Well, I’ll tell you. That formula is one of the governing dynamics for anything alcoholic that was ever put in a bottle or poured in a glass. Think of it like Newton’s Laws, but for booze.
How might this help you? You know your really hot dinner date likes dry Riesling, but hates anything sweet. You’re at the wine store. The wine guy is no where in sight and you’re picking her up at the train station in 5 minutes (yes, I know, I live in New York). How do you find the dry Riesling? The Germans aren’t making it easy with their multi-syllabic wine labels. “Mosel-Saar-Ruwer Zilliken Forstmiester Geliz Saarburger Rauch Auslaser” doesn’t exactly scream clarity. But the (federally required) alcohol % on the wine will reveal everything. And I’ll tell you why.
We pick grapes. We make juice. Juice is sugary. We add yeast (or they’re there already). They eat the sugar, producing CO2 , heat, and you guessed it, alcohol. Now, this formula happens at a very even rate (Yay! Chemistry!). For approximately every 17 grams of sugar per liter of the original juice, the yeast will turn that into 1% of alcohol. Isn’t that handy!
Most table wine grapes are harvested with between 10% and 15% potential alcohol (whites stick to the lower end of that bracket, reds to the higher). That means most grape juice intended to be table wine has 170 to 255 grams of sugar per liter before it’s fermented.
So, back to our friend with the date and the Riesling. He sees one Riesling at % 7.5 alcohol, and given that he knows the fermentation formula, he realizes that, “Wow, at only % 7.5 alcohol, there’s probably at least 51 grams/liter residual sugar in this! Way too sweet.”
Conversely, he knows that the higher the alcohol in the wine, the dryer (dryness/sweetness are opposed in wine). He finds a nice Riesling Kabinett at 11% alcohol, and picks up his date on time, they have a lovely dinner, fall in love, make babies, etc.
Keep the fermentation formula in the back of your head as I move on to other topics. It will be particularly important if I’m ever talking about sparkling wines, body, balance, distillation, and well, pretty much everything with which you get shitface (pronounced in the french manner “shee-fah-say”).