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Fermentation is generally considered anaerobic (without oxygen) breakdown of food. I assume rotting usually involves oxygen. (Maybe someone can nitpick that def

• Melatonic 3y ago
  Not always true - there is also aerobic fermentation. You are right in that many ferments require anaerobic conditions however it really just depends on the desired result and bacteria involved. Kombucha, for example, requires oxygen and is mostly an aerobic fermentation. In order to carbonate, however, it goes through a short anaerobic step at the end (which also causes it to switch from producing organic acids to producing alcohol). This is usually done during the bottling process since the bottle is sealed.
• giraffe_lady 3y ago
  That's the microbiological definition that a scientist would use. In food it is less well defined and usually just means something close to "intentional use of microorganisms in food production". Yeast does both aerobic and anaerobic metabolism but both are considered fermentation by bakers & brewers. Acetobacter is aerobic and vinegar making is considered fermentation. Koji is even farther out and usually still considered fermentation by fermenters.