ABSTRACT
Fermentation is a process in which microorganisms, in the absence of oxygen, generate energy by oxidizing carbohydrates and related compounds. It has been used since ancient times as an important method for preserving food. Vegetables, fruits, cereals, milk, and other raw materials have been treated in special ways in order to promote the growth of beneficial microorganisms while inhibiting the growth of deteriorating and pathogenic microorganisms. Fermentation will preserve the food, and it will also enhance the taste, aroma, texture, and nutritional value of the product. The preservation effect is the result of synthesis of lactic acid and heterofermentation-also, acetic acids and, some times, antimicrobial substances. Besides lowering the pH level, organic acids are also toxic for many microorganisms. It is also important that the fermentable carbohydrates are completely utilized by the fermenting microorganisms and thereby made unavailable for the undesirable microorganisms. In some products the addition of salt will increase the shelf life of the products by lowering the water activity. The natural habitats of lactic acid bacteria, yeast, and molds are most often plant materials. However, the type of organisms can vary considerably (1), depending on type of plant, climatic conditions, and available nutrients in the raw material. During some fermentations (e.g., fermentation of plant material such as cabbage, cucumbers, olives, soya beans, and coffee), several different types of microorganisms are required at the various stages of the fermentation process. In other fermentations (e.g., production of yogurt and beer), only a few different microorganisms are required.
