Fermentation is a process in which microorganisms, such as bacteria or yeast, convert carbohydrates into alcohol, gases, or other products. This occurs when certain enzymes break down sugars and other organic compounds under anaerobic conditions (in the absence of oxygen). Fermentation is commonly used in food production to create products such as bread, beer, wine, cheese, yogurt, sauerkraut, and kimchi. The process can also occur naturally in fruits or vegetables that have been stored for a long time, causing them to produce gases which cause spoilage.