The history of L. acidophilus goes a while back. Fermented milks had been made since early times when raw milk from animals was naturally preserved by common strains of Lactobacillus bacteria. These common strains made it possible to preserve fresh milk for many days without refrigeration. When the development of microbiological and nutritional sciences began in the late 19^th century, the technology that was needed in order to produce cultured dairy products was created. Finally, cultured products eventually became ethnic favorites and were introduced around the world. The fermentation process, which is the conversion of lactose (a milk sugar) to lactic acid, is the most important part of the production of cultured milk.  Today the fermentation process is used in many industries.