I’m thinking of like when you bottle wine that’s still fermenting, and it explodes. I understand that the fermentation process raises the air pressure inside the bottle. What I *don’t* understand is how? When you pump air into a balloon, the air pressure rises because there are *more* air molecules entering the balloon.
With wine in a bottle, you have a fixed amount of matter at a certain temperature. I don’t understand how fermentation could increase air pressure in a closed system?
In: Physics
When yeast ferments sugar it is producing more molecules of gas, and those gas molecules take up far more space than when the atoms that make it up were all bonded with other atoms as sugar.
18 ml of water takes up 22,400ml at room temp and standard air pressure when it is water vapor. Gases take up way more space per molecule than liquids. So if you use a closed container and convert liquid to gas, the pressure goes way up, equivalent to the pressure of having to squeeze a much larger volume of gas down to fit inside the container. You can create gas from liquid a couple of ways. You can heat the liquid, like when you boil water and turn the liquid water into steam, or you can use a chemical reaction that converts the liquid to some other chemical that is a gas. Fermentation does the second one.
The fermentation of sugar by yeast converts a molecule of dissolved sugar into two molecules of alcohol, specifically ethanol, a liquid, and two molecules of carbon dioxide, a gas. That carbon dioxide gas is what is responsible for the increased pressure, because it is essentially being compressed as it is forms so it all fits in the bottle.
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