Yeast Screen For Kvass And Optimization Of Its Fermentation Techniques

Kvass is a kind of soft drink made from grains, fruits and vegetables, which is fermented by bothlactic acid bacteria and yeasts. It is fresh as beer, mellow and cool as carbonated drinks. The traditionalkvass production is made of bread, and the color of kvass is similar to beer, brown-red. It is tasted fresh,sweet and sour-moderate and full with flavor of bread. However, this traditional procession has somedisadvantages: such as production is limited. In recent years, there were some factories for kvass inChina. Most of them are fermented by pure cultures from malt. Either the physicochemical or sensorycharacteristic is varied from brand to brand, especially different from the typical European kvass. So itis full of challenge and practical significance to solution the problem that the missing of typical flavor inmodern kvass.The component of malt wort was determined by raw material saccharifying process. On the otherhand, the wort components affect the fermentation and taste of kvass production. We improved thesaccharifying techniques for kvass as following: Firstly, Feeding malt at40℃for40min. Then makeprotein rest at46℃for50min. The malt was mashed at72°C until the Iodine seized reaction wascompleted. At last, heating up to100℃keep for20min.Because of the rich of metabolites, it is the yeast that play an important role on kvass qu-ality. We screened yeast for kvass from five different origins. We studied the alcohol, CO2, andester production, and the flocculation of yeast. Finally, we got one suitable strain called yeastY3for kvass fermentation.We used single factor experiment and response surface to optimize kvass fermentationtechnological parameter. We got the optimized fermentation parameter as follows: of the initial wortconcentration is5%, the vaccination is5%, yeast Y3（Saccharomyces cerevisiae）: lactobacillus L1（Lactobacillus plantarum）=1:1, the fermentation temperature is26°C, fermentation period is36h.We got kvass production with0.50%(V/V) alcohol,0.40%acidity (in terms of lactic acid), and fullwith typical bread flavor. This result showed that we could produce kvass full with typical flavor byscreen the suitable yeast.In this paper, we combined sensory evaluation of kvass with physicochemical indicators andorganic acids of kvass. We got result as follows: The sensory score of homemade and Europeankvass were higher than three different kinds of domestic commercial kvass, because the physicochemical indicators were more moderate and organic acid species were richer. This resultsturned out the sensory system reflect the quality including the shortcomings of kvass exactly. This resultagreed with the physicochemical testing and organic acid analysis results. So this sensory evaluatesystem would play an important role on kvass quality controlling and improvement.