The large and diverse group of microscopic foodborne yeasts and molds (fungi) includes several hundred species. The
ability of these organisms to attack many foods is due in large part to their relatively versatile environmental
requirements. Although the majority of yeasts and molds are obligate aerobes (require free oxygen for growth), their
acid/alkaline requirement for growth is quite broad, ranging from pH 2 to above pH 9. Their temperature range (10-
35°C) is also broad, with a few species capable of growth below or above this range. Moisture requirements of
foodborne molds are relatively low; most species can grow at a water activity (aw) of 0.85 or less, although yeasts