Microbiological deterioration in fruit juices, sugar-free soft drinks, jams and similar sugar products is generally carried out by osmophilic yeasts due to the high concentration of sugar. The determination of osmophilic yeast is mainly based on the principle of enumeration of osmophilic yeasts developing in sugary products with high sugar concentrations.

Yeasts are bacteria that love high sugar concentrations and grow very easily in sugary environments with low water activity that are unsuitable for bacterial growth. For example, bacteria do not develop under 0.9 water activity, but osmophilic yeasts show improvement even at 0.6 water activity values.

Yeasts benefit from large molecule compounds, primarily developing in fruits and producing alcohol. Smaller compounds formed by yeasts are used by molds. The pH values ​​in fruit juices and concentrates are in the range of about 3-4 and therefore these beverages are spoiled by yeasts. In fruit juices and concentrates, many varieties of yeast show an increase in the percentage of 20 glucose. A small number of yeast varieties can grow at the percent 60 sugar concentration, which leads to lower water activity. The physiological structure of these yeasts, which cause spoilage in sugary drinks, is responsible for resisting weak acids added as a protective additive against microorganisms and fermenting sugars. As a result of fermentation, the taste of fruit juice and concentrate is badly affected, the resulting carbon dioxide causes bombing in the package and discolorations in beverages are observed.

Yeasts enjoy sugary and acidic foods. However, yeast activities stop if there is too much alcohol in the environment. Yeasts need sugar to continue their activities. However, not all yeast varieties except osmophilic yeasts work at high sugar concentrations.

In advanced laboratories, studies are carried out for the determination of osmophilic yeast in sugary foodstuffs within the scope of microbiological analyzes. During these studies, standards and test methods published by local and foreign organizations are taken as basis.