Yeast has many appliances in food preparation: bread yeast results in fluffy and soft bread, and beer yeast and wine yeast ferment sugar into alcohol. However, there are also types of yeast that cause infections in humans, such as vaginal candidiasis (vaginal candida or thrush).
What is yeast?
Yeast is a collective term for many different types of single-celled fungi of the order Saccharomycetales, including more than 1,500 species. They live in different habitats, including in soil, plants and water, but also on the skin and in the intestines of warm-blooded animals, including humans. Yeast reproduce asexually, usually through budding or mitosis. History
Yeast has been used by humans to create bread and alcohol for thousands of years, but it was first microscopically observed in the late 17th century by the Dutch scholar Anton van Leeuwenhoek. However, it was Louis Pasteur, the famous 19th-century French microbiologist, who concluded that yeast were living micro-organisms. How do you get a yeast infection?
Yeast naturally occurs in the human body. The most common causes of a yeast infection is an overgrowth of the naturally occurring yeast fungi Candida albicans. This causes one of the most frequent vagina infections affecting women. Risk factors include pregnancy, excessive douching, wearing tight-fitting clothes, using perfumed soaps and oral contraceptives. Signs of a yeast infection include a white, curd-like discharge, itching and irritation. Male candidiasis is less common, but can be the result of a low immune system (for example in the case of AIDS and cancer patients) or intercourse with an infected person. Yeast infections can clear naturally, although anti-fungal drugs are commonly prescribed. Yeast as a culinary ingredient
The strains of yeast used in cooking are different from those causing infections, commonly belonging to Saccharomyces cerevisiae. When yeast comes in contact with sugar, it ferments, creating carbon dioxide and ethanol (alcohol) in the process. In the case of baking, tiny bubbles in the dough cause it to rise and expand, creating the fluffy texture usually associated with yeast-based breads. The bubbles in sparkling wine are the result of the fermentation process.
Uses of yeast
Yeast is an essential ingredient if you want to make your own bread or certain types of pastry. Most supermarkets sell dried yeast, which are ideal for home baking. Live yeast is harder to find, although an old-fashioned bakery can sometimes help. Self-raising flour does not contain yeast, but chemical leavening agents that embed small gas bubbles in the dough or batter. Yeast is also taken as a dietary supplement (known as brewing yeast) to provide B-complex vitamins, chromium, and selenium. That is also why Marmite is so good for you: it is made of yeast-extract!