Development and Shelf-Life Assessment of Kvass Beverage with Viable Microbial Flora

English. The fermentation process is deeply ingrained in human history, not only for preservation but also for enhancing the nutritional value of foods. In the contemporary context, the surge in global food waste is driving innovative solutions, with surplus bread being explored due to its high rate of wastage. Simultaneously, there is a growing interest in reviving traditional fermentation practices amid modern industrialization. This study seeks to blend these elements by repurposing surplus bread sourced from a local bakery for the production of a fermented kvass beverage containing viable microorganisms. The objectives of the study include recipe development and shelf stability assessment. The development was conducted with the utilization of surplus bread, malted grains, sugar, and orange zest. Shelf stability was assessed through alcohol concentration, viable count of lactic acid bacteria (LAB) and fungi, pH, total soluble solids, and qualitative assessment of carbonization levels, observed within different fermentation times, sugar concentrations, and storage temperatures throughout 4 weeks of storage. The study concludes that kvass with 2% sugar stored at 5°C maintained desired alcohol levels with 0.91% (v/v) after 4 weeks of storage and exhibited the most satisfactory levels for carbonation as well as pH. Higher survivability of LAB compared to fungi, especially at lower temperatures, was observed through microbial enumeration. However, challenges persist, particularly regarding sweetness perception, as 2% kvass exhibited the lowest °Brix value. To address this, the potential use of non-fermentable sugars is proposed.

English. Kvass is a traditional Eastern European drink made by fermenting stale bread, usually rye, which gives it a slightly sweet and tangy flavor. Think of it as a natural, mildly fizzy beverage created by letting bread and other ingredients sit together until they transform into a tasty drink thanks to the activity of microorganisms. Motivated by the rising consumer preference for natural and sustainably produced foods, the project aimed to help bring this traditional drink to the market in its original form, just like the homemade version. One that is preservative-free and contains live microorganisms known for their health benefits. Moreover, it aimed to use surplus bread, which is still edible but unsuitable for regular sale, to manage the issue of bread wastage, a product that is the fourth most wasted food globally. While these benefits benefit the consumer from a health perspective, they also introduce complexity to the production process and make standardizing the product challenging. The presence of live microorganisms means they remain active throughout the product's lifecycle and leads to variations in the sensory perception of kvass. When microorganisms are active they use sugars and convert them into acids, carbon dioxide, alcohol, and components that give the product characteristic flavor and aroma. Therefore, the characteristics of kvass vary depending on how long it is stored after bottling. For example, CO2 levels in kvass can continue to increase with longer storage. If these levels exceed what is desirable and the kvass bottle is opened, it can result in a reaction similar to shaking and opening a bottle of soda (although kvass itself doesn't need shaking). Additionally, continued microbial activity can produce more alcohol, which we want to keep within kvass's 0.5-1.5% range. In summary, the goal is to obtain kvass that remains balanced in acidity, sweetness, carbonation, and alcohol content for a consumer, by controlling factors such as sugar quantity, fermentation duration, and storage temperature (e.g., fridge or room temperature). We discovered that kvass made with 2% sugar and stored in the fridge for a month retained desired alcohol levels and carbonation, and offered the best balance of flavors and acidity. However, the drink was less sweet than some might prefer. One potential solution to address this could be using sugars that are not easily converted by microorganisms but still impart a sweet sensation. This work can be used as a starting point for further development of kvass to produce a sensory-acceptable beverage that maintains live and active cultures and helps the industry bring its benefits to consumers. This could provide consumers with a healthier, more authentic fermented drink and at the same time address the global challenge of food waste.