General Information

During growth on the nutrient medium of Compact Dry YMR, colonies of yeasts and molds show different color reactions and therefore they are easy to differentiate. The chromogenic substrate X-Phos develop a blue green color with nearly all yeast colonies. Molds will appear quickly as light blue, diffuse looking colonies and later on form their typical three-dimensional structures in the air space between the nutrient pad and plate cover. The coloration of the air structures might be different according to the special type of mold. Growth of bacterial species on Compact Dry YMR is inhibited by antibiotics which are added to the medium.

Yeasts

Yeasts are facultative anaerobe, monocellular fungi (Ascosporidae), fermenting sugar substrate to CO2 and H2O. Under anaerobic conditions yeasts ferment sugar to alcohol and CO2. Those qualities are commercially used in the brewing, wine and baking industry. Saccharomyces cerevisiae is the most common strain used for industrial purposes. In terms of food spoilage, genera of Candida play a major role. This germ is located in human and animal mucosa (nose, throat).

Molds

The term “mold“ is commonly used for the visible part of the fungi present on the surface of contaminated food. Under the surface the fungi forms mycelium, which cannot be recognized with the naked eye. Specific molds, as well as yeast, are used for industrial purposes (e.g. cheese production). Harmful genera of molds exist as well and are able to produce toxins (mycotoxins). Almost all molds have an allergenic potential related to their spore forming capabilities. Besides food spoilage, molds are environmental concerns when buildings become infested by molds.