Influence of different technological parameters in the evolution of pH during fermentation of kefir

Kefir, a refreshing fermented milk with a slightly acidic taste, is made from kefir grains, a complex and specific mixture of bacteria and yeasts held together by a polysaccharide matrix. The object of this study was to determine the influence of grain percentage, shaking and temperature on the continuous evolution of pH during kefir fermentation. To this end, the variations of the kefir's pH were studied, modifying 3 elaboration factors: dose of grains (1, 5, 10, 20%), temperature (20 and 25 degrees C) and shaking (not shaking and 50 strokes/min). The obtained results demonstrate that the factors studied have significant effects on the pH evolution during kefir fermentation. The acidification speed increased with the amount of grain, and all samples made with shaking showed higher pH values. The fermentation temperature affects distinctly both, the total capability of acidification and the acidification speed. These technological parameters should be modified depending on whether a more or less acidic drink is wanted.