People have been fermenting vegetables for centuries to increase the stability of fresh foods, to make the foods safer to eat in the absence of refrigeration and to enhance their flavor. Today, vegetable fermentation is done on a large-scale setting in factories as well as in households across the world. In the United States, the primary vegetables fermented are cucumbers (pickles), cabbage (sauerkraut and Kimchi) and olives. In many parts of the world, especially in developing countries where refrigeration is not common, fermented foods constitute a major portion of the diet. During vegetable fermentation, mainly bacteria and, at times, yeast break down vegetable sugars into acid, carbon dioxide gas and other flavor compounds. The acid produced gives the vegetable tartness and also keeps the food safe by preventing harmful bacteria from growing. The acid and carbon dioxide also keeps spoilage microorganisms from growing so fermented vegetables can last much longer than their fresh counterparts. Fermentation changes the flavor of vegetables as well as increases the nutritional content by producing B-vitamins and increasing the digestibility of the vegetable by breaking down vegetable fiber.