Yeast is used to ferment sugar into alcohol through the brewing process.
1. Get sugar out of barley or grapes.
Beer: made from grain, usually barley, allowed to germinate a few days, starch in grains broken down into sugar by enzymes. Grains dried in kiln - malting. Malted grain mashed and water added to make sugary solution with lots of bits, sieved to remove bits. Hops added to mixture for bitter flavour.
Wine: Grapes mashed and water added.
2. Yeast added and mixture incubated (kept warm). Yeast ferments sugar into alcohol. Fermenting vessels designed to prevent unwanted microorganisms and air getting in.
Rising concentration of alcohol in fermentation mixture due to anerobic respiration eventually starts…