MICROBIOLOGY Study Guide - 2012

CHAPTER 15. FOOD MICROBIOLOGY

15.10. MICROBIOLOGY OF KVASS

Kvass is a traditional Slavic beverage produced by incomplete alcoholic and Lactic acid Fermentation of kvass wort. The alcohol content in kvass typically ranges around 0.5%. The primary specific microorganisms driving the fermentation are kvass Yeasts of the species S. cerevisiae and Heterofermentative lactic acid Bacteria of the species L. fermentum, strains 11 and 13. The yeasts ferment the sugars in the kvass wort to produce alcohol and CO₂, while the lactic acid bacteria accumulate lactic, acetic, and succinic acids, alcohol, CO₂, and secondary Aromatic Compounds during the fermentation process. Compressed baker's Yeast may also be used to make kvass; however, this can impart an undesirable yeast flavor and reduce the shelf-life of the beverage. The raw Materials for kvass production include rye malt, rye flour, barley malt, sugar, dry kvass, and kvass wort concentrate derived from rye malt with The addition of rye or corn flour.

The technological process for producing traditional bread kvass consists of the following stages:

Class="center">Wort preparation → Preparation of sugar syrup and caramel coloring → Propagation of pure cultures (PC) of yeast and lactic acid bacteria → Preparation of combined PC starter for yeast and lactic acid bacteria → Wort fermentation → Blending of fermented wort → Bottling of kvass into consumer packaging.

For kvass production, the yeast and lactic acid bacteria are initially propagated separately until the volumes required for inoculation are reached. A combined starter culture containing both organisms is then prepared and added to the kvass wort at a 4% inoculation rate. The initial yeast concentration in the kvass wort is (25–50) × 10⁶ Cells per 1 cm³.

During the preparation of sugar syrup, caramel coloring, and blending stages, contamination of kvass by extraneous microorganisms may occur due to breaches in Sanitary and hygienic manufacturing practices. Of particular importance in reducing the shelf-life of kvass is The process of filling it into improperly washed and unsterilized containers.

Kvass spoilage is most frequently caused by the following groups of microorganisms.

1. Slime-forming bacteria — Leuconostoc mesenteroides, B. subtilis. These bacteria possess The ability to synthesize Polysaccharides, resulting in a ropy texture in the kvass and a diminished perception of sweetness. To prevent this type of spoilage, manufacturing protocols must be strictly followed, and the sugar syrup should be boiled for at least 40 minutes.

2. Acetic acid bacteria — Acetobacter aceti, Gluconobacter oxydans. They oxidize alcohol into acetic acid, which increases product acidity, lowers density, impairs flavor, and leads to The formation of a surface film. Maintaining strict sanitary and hygienic production standards is a prerequisite to prevent the proliferation of this group of bacteria.

3. Molds of the genera Penicillium, Aspergillus, Fusarium, and others impart an unpleasant moldy odor and taste to the finished product. Preventive measures against this defect include thorough washing and disinfection of production facility floors and walls, storage tanks and equipment, as well as air filtration and sterilization.

4. Wild yeasts — Candida crusei, C. guillermondi, C. mycoderma, and others. Their proportion in the combined starter should not exceed 0.5%. These yeast species oxidize alcohol to form CO₂ and H₂O, form a white wrinkled film On the surface of the kvass, and suppress the growth of cultivated yeasts.

To prevent the growth of extraneous microorganisms during kvass production, routine sanitary and microbiological monitoring must be applied to: drinking Water, granulated sugar, sugar syrup, kvass wort concentrate, finished kvass wort combined with sugar syrup, bottles, sealing materials, equipment rinse water, and tanker trucks.

The determination of total viable count (TVC) is not required for unpasteurized bread kvass. In filtered and pasteurized kvasses, the TVC must not exceed 10 CFU/cm³; coliforms must be absent in 10 cm³; pathogenic bacteria, including Salmonella, must be absent in 25 cm³; and the combined yeast and mold count must not exceed 100 CFU/cm³.