In food microbiology studies, mold and yeasts are generally handled together. There are two reasons for this. The first reason is that molds and yeasts come from the fungal family. The second reason is that yeasts and molds develop on the media in such a way that they can be easily separated from each other. Molds are multicellular fungi and can form a community. Yeasts are unicellular and generally do not form a community. Some varieties of yeast have great economic importance in the production of bread, wine and beer. Some mold varieties are used in cheese making. Nevertheless, it is a fact that many mold and yeast species create undesirable conditions in the fermentation and food sector. Such yeasts and molds lead to degradation of foodstuffs.

Molds and yeasts can grow in a wide range of pH values, storage temperature and water activity. It can easily develop in high salt and sugar containing environments. Mold and yeasts causing spoilage create bitter taste and bad odor in foods. Some mold types secrete toxic substances and lead to poisoning if these foodstuffs are consumed.

Mold and yeast formation usually occurs when:

• Outdoor marketing of foodstuffs
• Exposure of foodstuffs before packaging due to technologies used in production
• Even if foodstuffs are pasteurized, contamination from materials used in packaging
• Food processing other than washing and cooling or freezing processes have been applied

In mold and yeast counts, rapid test methods are used as well as advanced test methods. In the authorized laboratories, mold and yeast counting studies are performed with rapid test methods within the scope of microbiological analyzes. During these studies, standards and test methods issued by domestic and foreign organizations are followed. TS ISO 21527-1 and TS ISO 21527-2 standards are taken into consideration.