Fermentation a word used loosely to describe desirable changes brought about by living micro-organisms (yeasts, moulds, and bacteria) in food and drink. Broadly speaking, it is the conversion of carbohydrates (including sugars) into ethanol (alcohol), carbon dioxide, or organic acids (especially lactic). Usually, but by no means invariably, the process occurs under anaerobic conditions. The term is often extended to changes caused by non-living enzymes, for example in the ‘fermentation’ of black tea. When micro-organisms or enzymes cause undesirable changes, for example making food go bad, what happens is called spoilage rather than fermentation (although one man’s spoilage may be another’s deliberate intent).