Water kefir is a water-based fermented beverage obtained through the fermentation of sugary liquids by lactic acid bacteria, bifidobacteria, and yeasts of the genus Saccharomyces. Its low-calorie content, absence of lactose and cholesterol, and provision of a probiotic source for vegan and vegetarian individuals make water kefir an alternative to milk-based kefirs. Water kefir exhibits high adaptability to fermentable sugar sources, and sensory and functional diversity can be achieved by using different substrates.

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History

Water kefir holds a traditional place among fermented beverages. Although its precise origin is not fully established, it parallels fermented drinks derived from plant sources worldwide, particularly in the Middle East and some tropical regions. Traditionally, it has been consumed as a home-fermented beverage and possesses a flexible microbial structure capable of adapting to various fruit and sugar sources.

Microbial Structure of Water Kefir Grains

Water kefir grains contain a complex microbial structure. Lactic acid bacteria exhibit homofermentative or heterofermentative characteristics, produce exopolysaccharides (EPS) from sucrose, and support the texture of the beverage. Through amino acid biosynthesis and organic acid production, the symbiotic interaction of the microflora promotes yeast growth. Bifidobacteria, due to their obligate anaerobic nature, produce acetic acid, inhibit pathogens, and contribute to the balance of intestinal microbiota.

Yeasts, particularly Saccharomyces cerevisiae, thrive in high-sugar environments; by producing ethanol, sorbitol, and aroma compounds, they create the beverage’s carbonated, refreshing, and characteristic flavor. Acetic acid bacteria convert ethanol to acetic acid under aerobic conditions, providing the beverage’s acidic profile and supporting grain development. Symbiotic relationships exist among microorganisms in water kefir; lactic acid bacteria acidify the environment to facilitate yeast growth, while yeasts enhance metabolite production by lactobacilli.

Water kefir grains serve as an alternative to milk-based kefirs due to their low-calorie content and absence of lactose and cholesterol, offering a valuable probiotic source for vegan or vegetarian individuals. The growth rate of grains and the density of viable microorganisms are influenced by factors such as grain size, surface area, medium pH, mineral content, and buffering capacity. Smaller grains exhibit higher metabolic activity due to their increased surface area and can enhance the quantity of fermentation products. In this regard, water kefir grains represent both a health-supportive element and a fundamental component actively participating in the fermentation process.

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Preparation of Water Kefir

Ingredients

• Water (preferably mineral or purified water)
• Sucrose or fruit sugars
• Dried fruits (such as dried figs, apricots, raisins, etc.)
• Water kefir grains

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Preparation Method

In the production of water kefir, water and sugar are first mixed at an appropriate temperature. The sugar is broken down by yeasts into glucose and fructose. Water kefir grains are then added to this mixture, and the microorganisms within the consortium proliferate and produce metabolic products through their symbiotic interactions. During fermentation, dried fruits serve as sources of vitamins, minerals, and nitrogen for the microorganisms and interact with their metabolites.

Fermentation typically begins with the production of homopolysaccharides within the first 24 hours, followed by the formation of glycerol, acetic acid, and mannitol by the 72nd hour. By the eighth day, the accumulation of lactic acid and ethanol is observed. The fermentation temperature is maintained between 25–32 °C. Upon completion of fermentation, the grains are filtered out, and the liquid is consumed, while the grains can be cleaned and reused.

Fermentation conditions directly influence the viability of the grains, metabolite production, and the distribution of microorganisms. When the pH falls below 3.5, the growth of pathogens is inhibited.

Fermentation Products and Polymers

Water kefir is fermented using sucrose and other sugar sources. During fermentation, sugars are broken down into glucose and fructose. Lactic acid, acetic acid, and other organic acids are produced. Ethanol and carbon dioxide are also generated, imparting a lightly carbonated texture and characteristic aroma to the beverage. Exopolysaccharides (α-glucans, fructans) are synthesized, supporting both the structural properties of the beverage and its probiotic efficacy. The exopolysaccharides formed during water kefir fermentation, including α-glucans and fructans, enhance the consistency and probiotic functionality of the beverage. Organic acids contribute to pH reduction, inhibiting pathogen growth and defining the flavor profile. Additionally, ethanol, CO₂, sorbitol, and fruity esters contribute to the carbonated and refreshing characteristics of water kefir. Fermentation parameters, including temperature, sugar concentration, and oxygen level, directly influence microbial viability and metabolic activity.

Nutritional Content

Water kefir is rich in vitamins, minerals, dietary fiber, and antioxidants due to the inclusion of fermented fruits and sugar sources. Dried fruits not only fulfill the nutritional requirements of microorganisms but also provide functional nutrients to the consumer at the end of fermentation. These properties make water kefir a suitable alternative to milk-based kefirs for individuals with lactose intolerance or cholesterol concerns.

The probiotic effects of water kefir derive from its content of lactic acid bacteria (LAB), Bifidobacterium species, and Saccharomyces yeasts. These microorganisms support intestinal flora, stimulate the immune system, and may inhibit the passage of certain pathogens. Moreover, α-glucans produced in the presence of sucrose, being non-digestible, help maintain the balance of intestinal microbiota.

Health Effects

Antioxidant Activity

Water kefir can stabilize free radicals, thereby reducing cellular and tissue damage. This activity may lower the risk of diseases such as cancer, arteriosclerosis, and arthritis. The metabolites produced during fermentation and the exopolysaccharides associated with the microorganisms are primarily responsible for this antioxidant effect.

Probiotic and Gut Health

Lactic acid bacteria and yeasts support the gut microbiota and stimulate the immune system. Regulation of α-glucosidase enzyme activity may contribute to the maintenance of balanced blood glucose levels. Non-digestible α-glucans promote the proliferation of beneficial bacteria in the intestine.

Anti-hyperglycemic and Hypolipidemic Effects

Certain lactic acid bacteria isolated from water kefir can regulate glucose metabolism, contributing to blood sugar control and positively affecting lipid levels. Positive outcomes regarding blood glucose regulation have been observed in obese mice supplemented with water kefir-derived strains.

Antimicrobial Activity

Water kefir exhibits inhibitory effects against significant pathogens, including Streptococcus pyogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli, Listeria monocytogenes, and Candida albicans. This property enhances the value of water kefir from a food safety perspective.

Functional Food Potential

Water kefir can be utilized as a probiotic beverage alternative to milk-based kefirs. It is particularly suitable for individuals with lactase deficiency, milk allergies, or those adhering to a vegan diet. The beverage can be diversified with different sugar sources and fruit–vegetable purees, enabling the development of new drink varieties. While water kefir can be produced on a domestic scale, industrial production requires detailed research to maintain grain viability, ensure microbial balance, and comply with safety standards.