Yeast

A group of single-celled fungi that reproduce by budding. Most yeast are harmless (some are used in baking and brewing). Yeast is commonly present on normal human skin and in areas of moisture, such as the mouth and vagina, usually without causing any problems. However, yeast can produce disease in people. For example, the yeast Candida (once called Monilia) causes thrush (oral infection) and diaper rash in infants, fingernail infections, vaginal area infections in women after puberty, and a host of problems in patients with immune deficiency.

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A general term denoting true fungi of the family Saccharomycetaceae that are widely distributed in substrates that contain sugars (such as fruits), and in soil, animal excreta, the vegetative parts of plants, etc. Because of their ability to ferment carbohydrates, some yeasts are important to the brewing and baking industries. [A.S. gyst]

- brewers' y. y. produced by Saccharomyces cerevisiae; a by-product from the brewing of beer.

- compressed y. the moist living cells of Saccharomyces cerevisiae combined with a starchy or absorbent base.

- cultivated y. a form of y. propagated by culture and used in breadmaking, brewing, etc.

- dried y. the dry cells of a suitable strain of Saccharomyces cerevisiae; brewers' dried y., debittered brewers' dried y., or primary dried y. are the sources of dried y.; it contains not less than 45% of protein, and in 1 g not less than 0.3 mg of nicotinic acid, 0.04 mg riboflavin, and 0.12 mg thiamin hydrochloride; used as a dietary supplement.

- primary dried y. a source of dried y.; obtained from suitable strains of Saccharomyces cerevisiae grown in media other than those required for the production of beer.

- wild y. any of the uncultivated forms of yeasts, useless as ferments and sometimes pathogenic.

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yeast 'yēst n

1) a unicellular chiefly ascomycetous fungus (as of the family Saccharomycetaceae) that has usu. little or no mycelium, that typically reproduces asexually by budding, and that includes forms (as Saccharomyces cerevisiae) which cause alcoholic fermentation and are used esp. in the making of alcoholic beverages and leavened bread

2) a yellowish surface froth or sediment that occurs esp. in sugary fermenting liquids (as fruit juices) and consists chiefly of yeast cells and carbon dioxide

3) a commercial product containing yeast cells in a moist or dry medium

yeast·like -.līk adj

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n.

any of a group of fungi in which the body (mycelium) consists of individual cells, which may occur singly, in groups of two or three, or in chains. Yeasts reproduce by budding and by the formation of sexual spores (in the case of the perfect yeasts) or asexual spores (in the case of the imperfect yeasts). Baker's yeast (Saccharomyces) ferments carbohydrates to produce alcohol and carbon dioxide and is important in brewing and breadmaking. Some yeasts are a commercial source of proteins and of vitamins of the B complex. Yeasts that cause disease in humans include Candida, Cryptococcus, and Pityrosporum.

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(yēst) an imprecise term used to refer to a member of one of the two largest groupings of fungi (the other being molds); yeasts are single-celled, usually rounded fungi that produce by budding (blastospore formation). Some transform to a mycelial (mold) stage under certain environmental conditions, while others always remain single-celled. Many of the perfect yeasts are classified in the order Endomycetales, and many imperfect ones are classified in the form-family Moniliaceae. A few yeasts are pathogenic for humans.