I’ve been learning a thing or two about winemaking lately. I will now share one of those things with you.
The process that converts grape juice (or other fruits, or grains) into wine is ethanol fermentation. Here’s the formula:
C6H12O6 –>2 CO2+ 2C2H5OH + Energy Released (118 kJ mol-l)
At the most basic level, that’s all there is to it: sugar gets converted into carbon dioxide gas, ethyl alcohol and energy.
A little bit more specifically, though, here’s what happens:
When yeast come in contact with a high-sugar liquid, it starts multiplying. As it multiplies, it secretes enzymes — 5 of em. It’s these enzymes that actually do the work of breaking down the sugar to glyceric acid and glycerol and then to Pyruvic Acid (through a process called glycolysis) and then breaking that down to acetaldehyde + carbon dioxide (which bubbles away), and then converting the acetaldehyde into ethyl alcohol. What exactly are glyceric acid, glycerol, pyruvic acic, and acetaldehye, you ask? I don’t know yet, but I’ll find out.
Interestingly enough, another kind of fermentation, Lactic acic fermentation, happens in muscles of animals when the muscles need energy faster than the blood can supply oxygen.
Another interesting piece of info is that the exercise/>lose-weight-exercise/>weight of the carbon dioxide that’s produced is almost the same as the exercise/>lose-weight-exercise/>weight of the alcohol that’s produced. So, if you start with 10 lbs of sugar in your juice, you’ll end up with 5 lbs of alcohol and 5 lbs of CO2 that will have escaped. So, the crazy thing is that the wine weighs less than the juice did, but you still have the same volume. So, what changed? The density!
Specific Gravity is the ratio of the density of a liquid in relation to water. The grape juice that you start with might have a specific gravity of 1.081, and the wine you end up with might have a specific gravity of .990. From knowing how much less dense the wine is than the juice, you can figure out how much alcohol it has! Crazy.
My first wine, the Martian Red Australian Shiraz was made from juice with a specific gravity of 1.080. When it was done, it had a specific gravity of .995. One formula for calculating the alcohol content is ((Starting SG *100) – (Final SG *100)) / 7.36 . So, 1080 – 995 = 85 / 7.36 = 11.548%!
I’m going to update this article as I learn more. There’s a LOT of misinformation and conflicting information out there about exactly how fermentation works and exactly how winemaking works. I’m hoping to clear some of that up here as I learn more and make more wine.