The first step is to homogenize the milk to 8% dry matter and held by heat treatment at 90-95 °C for 5-10 minutes. The cooled at 18-24 °C and inoculated with 2-8% kefir cultures in tanks.
Kefir is produced by the fermentation of lactic acid and alcohol by mesophilic bacteria and yeasts, respectively. The vital function of lactic acid starters is for fermentation of lactose into lactic acid. In addition, they also contribute to flavor, aroma and alcohol production, while inhibiting interference of spoilage microorganisms.
Kefir can also be prepared by inoculating milk with kefir grains which are a combination of bacteria and yeasts in a symbiotic matrix. Kefir grains consist of protein and polysaccharide matrix containing different species of yeasts, LAB, acetic acid bacteria, and mycelial fungi.
After heat treatment and cooling to 22 ºC and then later inoculated separately with 1.5 % (w/v) kefir grains previously activated.
Fermentation was performed at thermostatic bath at 22 ºC for 48 h. The kefir grains were then separated from the product with a sieve and then preserved in sterilized skimmed milk under refrigeration at 4 ºC for future fermentations. The product was cooled and stored at 4 ºC for the final 28 days.
Microorganisms involved in kefir production secrete exopolysaccharides that accumulate along with proteins and fat molecules to form kefir grains. Further, growth of kefir grains occurs by the accumulation of microbial biomass on the pre-existing kefir grains during kefir production.
Kefir produced through the fermentation of milk by the microorganisms is a white or yellowish colored, sour, carbonated and a mild alcoholic beverage.
Processing of Kefir
