Saccharomyces is a genus of fungi that includes many species of yeasts. It is a common symbiotic yeast that inhabits the gastrointestinal tract, respiratory tract, and the vaginal mucosa and can only infect the host under specific conditions. They are unicellular and saprotrophic fungi. The inability to use nitrate and the ability to ferment various carbohydrates are typical characteristics of Saccharomyces.
Many members of Saccharomyces are considered very important in food production. It is known as the brewer's yeast or baker's yeast. The brewing strains can be classified into two groups; the ale strains (Saccharomyces cerevisiae) and the lager strains (Saccharomyces pastorianus). Lager strains are a hybrid strain of S. cerevisiae and S. eubayanus and are often referred to as bottom-fermenting. In contrast, ale strains are referred to as top-fermenting strains, reflecting their separation characteristics in open square fermenters.
S. cerevisiae has been an essential component of human civilization because of its extensive use in food and beverage fermentation in which it has a high commercial significance. Regarding the beverage industry, S. cerevisiae is involved in the production of many fermented beverages, distilled beverages, and alcoholic beverages. S. cerevisiae is the most common yeast species in bread and sourdoughs. It has been used as a starter culture since the 19th century, where Baker's yeasts were obtained from the leftovers of the beer manufacture.