Yeast belongs to fungi, and fungi all have cell walls. Yeast is a single-celled microorganism that belongs to the fungi class of higher microorganisms. There is a nucleus, a cell membrane, a cell wall, mitochondria, the same enzymes and metabolic pathways. Yeast is harmless and easy to grow. Yeast is found in the air, soil, water and in animals. It can survive with or without oxygen.

Yeast is a facultative anaerobic organism. No obligate anaerobic yeast has been found. When there is a lack of oxygen, fermentative yeast obtains energy by converting sugars into carbon dioxide and ethanol (commonly known as alcohol).

Most yeasts can be isolated from sugar-rich environments, such as some fruits (grapes, apples, peaches, etc.) or plant secretions (such as cactus juice). Some yeasts live inside insects. Yeast is a single-cell eukaryotic microorganism. Its shape is usually spherical, oval, sausage-shaped, oval, lemon-shaped or lotus-shaped, etc. It is much larger than the single-celled individuals of bacteria, usually 1 to 5 or 5 ~20 microns. Yeast has no flagella and cannot swim. Yeast has a typical eukaryotic cell structure, including cell wall, cell membrane, nucleus, cytoplasm, vacuoles, mitochondria, etc., and some also have microbodies.

The genetic material of yeast consists of: nuclear DNA, mitochondrial DNA, and special plasmid DNA.

Most yeast colonies have similar characteristics to bacteria, but are larger and thicker than bacterial colonies. The surface of the colony is smooth, moist, sticky, and easy to stir up. The texture of the colony is uniform, and the front and back sides, edges, and center are The colors are very uniform, most of the colonies are milky white, a few are red, and some are black.