Kefir (or keefir, kephir) consists of a number of bacterial organisms and yeast, which live together in grainy clumps or cauliflower-like structures. Kefir is a symbiotic system – the bacteria and yeast depend upon each other to provide the necessary food and conditions for survival. A probiotic drink, also known as Kefir, is produced when the kefir grains are used to ferment various kinds of milk (cow, goat, sheep and so on). Kefir grains that grow and flourish during the fermentation process can then be collected and used as a ‘starter culture’ for another round of drink production. This is the same principle that is used with sour-dough bread starter, or when culturing a new batch of yoghurt from a scoop of the old.

Kefir has a uniform, slightly creamy consistency, a sour refreshing flavour, with a slight subtle aroma of fresh yeast [or a very subtle beer-like aroma]. Kefir also has a slightest hint of a natural effervescent zesty tang. There is an assortment of some 40 aromatic compounds contributing to the unique flavour and distinctive pleasant aroma of kefir. Rounding this off, kefir contains between 0.08% to 2% alcohol. However, about .08 to .1% alcohol is a realistic figure for 1-day cultured kefir. Whereas kefir stored for a number of days after separating the natural mother-culture, kefir grains [see following], contains up to 2 and possibly 3% alcohol, depending on milk-type and ripening conditions.

History

• Ancient fermented milk product, with origins in northern Caucasus Mountains
• Variations in China, Tibet, Russia, Ireland, Taiwan and Turkey
• Microbiological Composition varies depending on region.
  

Science

• Many different bacteria and yeast in various forms of kefir.
• Bacteria include Zygosaccharomyces sp., Candida sp., Lactococcus sp. and Lactobacillus sp.
• More than 23 different yeast species have been isolated from kefir grains, but the predominant species are Saccharomyces cerevisiae, S. unisporus, Candida kefyr, and Kluyveromyces marxianus ssp. Marxianus
• The microbial diversity means Kefir from different regions has different biological and biochemical properties and interacts with human digestion in different ways.

Nutrition

Nutritional benefits that may be attributed to kefir include:

• Some studies suggest that probiotic bacteria in kefir consumers’ gut are abundant and are correlated with health improvement. It has been demonstrated that the cell-free fraction of kefir enhances the ability to digest lactose relieving symptoms.
• Microorganisms in the kefir grains produce lactic acid, antibiotics and bactericides, which inhibit the development of degrading and pathogenic microorganisms in kefir milk .
• Increased interest in probiotic strains from kefir suggest a capacity to lower cholesterol levels.

Kefir Grain

Kefir grain formation is not well understood. It is thought to occur in stages, each stage adding layers to the kefir structure, and resulting from the actions of a particular set of microorganisms. Lactobacillus organisms auto-aggregation into tiny cell clusters. Other microrganisms respond to the surface properties of these clusters and thin biofilms begin to develop. Next, a three-dimensional structure forms as yeasts and yet more organisms associate with the biofilms, kefir yeast and Lactobacillus sp. increase, and milk components begin to accumulate on the granules’ surfaces. Thus, kefir ‘grains’ are in fact three dimensional matrixes containing varied layers of yeast, bacteria and milk components.

The ‘matrix’ of a kefir granual is a living one. The bacteria and yeast share bioproducts, providing each other with the necessary energy sources and growth factors. The symbiotic chemistry that occurs includes lactic and alcoholic fermentation,  and it is this fermentation that produces the kefir milk product itself.

Production Process

There are many variations on Kefir production. The culture may be a ‘plant’ – a lumpy product a bit like a piece of cauliflower or consist instead of kefir grains. It may be provided in a liquid medium or as dried kefir granules, much like dried yeast. Dried kefir grains may take two or three uses before they revive to full potential.

• Work in a hygienic environment with clean utensils.
• Drain kefir using a sieve or strainer
• Add kefir to 300ml of full-cream milk
• Cover and stand at room temperature for 24 to 72 hours. Clots of casein (milk protein) will form as fermentation progresses. At higher ambient temperature, this process may be faster. Longer fermentation results in greater separation and a ‘tarter’ and more alcoholic product.
• Strain the liquid Kefir into a bowl – it’s now ready for consumption
• Rinse the remaining kefir culture until the rinse water runs clear.  

Notes:
The kefir culture increases in volume with use as it traps casein proteins from the milk. There will therefore be more culture for the given volume of milk each time, so the fermentation will be faster and the aroma and taste stronger.
If ‘plant’ kefir is used, you may notice it sink to the bottom of the container initially and later rises as carbon dioxide (CO2) is produced during the fermentation process.

Variations

Kefir can be fermented from 12 to 72 hours. Shorter times produce a lighter, sweeter and milder product. Some people report a mild laxative effect at 12 hours progressing to a mildly constipating effect at 70 hours.

In general, the kefir is left undisturbed while fermenting. You may wish to experiment with shaking the container at intervals. This will reduce the casein clots, release some CO2, increase the alcohol content and alter the final aroma and texture.

Another option is to ferment the kefir for 24-48 hours then remove the culture and allow the milk product to ripen at cool temperatures (10 -18deg C). The result is a thicker, yeastier product, with a higher alcohol content.

Storing Kefir in the refrigerator immediately after brewing will reduce the alcohol content and produce a milder aroma.