The microbiological quality of canned fruits and vegetables directly depends on the properties of the raw materials and additives and the storage and transport conditions. The microorganisms in the raw material are significantly destroyed during the pre-preparations such as washing, peeling and scalding before the heat treatment applied in the production of canned food. However, if the heat treatment is delayed, the microorganisms may start to multiply during the holding step. Clean and unhygienic tools and materials as well as additives used in production are also important causes of contamination.

Microorganisms proliferating in the can can start to damage the food. If the deterioration is caused by a gaseous microorganism, the upper and lower lids of the can begin to swell. This is called bombing. Such foodstuffs are degraded and inexhaustible. However, if the deterioration occurs due to a non-gaseous microorganism, the outer appearance of the can will not change despite the deterioration of the food. In this case, deterioration is noticed when the box is opened. This kind of deterioration is called flat-sour or flat souring. In general, these deteriorations are caused by spore thermophile bacteria.

The food in the can starts to sour because of the lactic acid formed by the microorganisms. These deteriorations are common in canned beans, peas and corn. The degradation factor is bacillus. Smooth souring can also be seen in canned tomatoes and tomato juices. The deterioration factor in this case is the bacillus coagulans bacteria, a facultative thermophile microorganism.

Therefore, thermophile bacteria are emphasized in the production of canned foods in the food sector. These bacteria form acid from carbohydrates without gas formation. However, the generated acid also inhibits its development and stops its activities after a while.

In advanced laboratories, within the framework of microbiological analysis, flat-sour, ie the number of bacteria for flat souring studies are carried out. These relevant standards and analysis methods are complied with.