Background:  Yeasts & molds constitute a large and divergent group of microorganisms consisting of several thousand species.  Most can be detected in soil and air.  Because of their heterotrophic nature and their ability to adapt to a wide range of environmental conditions, these fungi are frequently encountered as actively growing contaminates in and on various commodities including foods, inadequately cleaned floor processing equipment, and food storage facilities.

Molds, and to a lesser extent, yeasts can initiate growth over a wide pH range, from below pH 2 to above pH 9.

Yeasts and molds can cause various degrees of food decomposition.  Invasion and growth may occur on virtually any type of food if environmental conditions are not limiting.

Analysis Description:  The 3M Petrifilm Rapid Yeast and Mold Count Plate is a sample-ready culture medium system which contains nutrients supplemented with antibiotics, a cold-water-soluble gelling agent and an indicator system that facilitates simultaneous yeast and mold enumeration.

The sample is diluted with a buffer, blended, and an extracted amount is plated on the Petrifilm, many times in a serial dilution format.  Depending on the matrix, the samples are either incubated at 25°C for 48 to 72 hours or 28°C for 48 to 72 hours.