Kefir ( Russian Кефи́р kefir ; internationally also kephir ) is a thick sour milk product with a low carbonic acid and alcohol content , which originally comes from the Caucasus region. Similar to yogurt is produced Kefir by a fermentation process ( Fermentation ), but to the next lactic acid bacteria such as Lactococcus lactis and Lactobacillus acidophilus also yeasts such as Candida utilis , Saccharomyces fragilis , Kluyveromyces marxianus (also known as Candida kefyr ) and Kluyveromyces lactis are involved which form carbon dioxide and alcohol . Along with choormog and kumys, kefir is one of the dairy products that are made from yeast.
After kefir had initially found little distribution outside the Caucasus region, it was from 1908 in Russia by doctors as a healing drink for patients with e.g. B. administered intestinal discomfort.
Kefir has a characteristic aroma compared to other sour milk products. Like all sour milk products, it has the advantage that it is easier to digest (at least for adults) and that it has a much longer shelf life than raw milk . Kefir has a typical pH of 4.2 to 4.6.
Milchkefir is created by about one to two days cow, goat or sheep's milk with Kefirknollen added. For the production of the related product Kumys is mare's milk used. If long-life milk or pasteurized milk is not used for production , various sources recommend boiling the raw or preferred milk beforehand in order to suppress the multiplication of undesirable microorganisms, but this is not necessary. Coconut milk and other plant-based drinks can also be fermented into kefir.
The approach is then left to stand. Many instructions provide for a single stirring after a few hours. Optimal temperatures are between 10 and 25 ° C. The milk is fermented . The alcohol content of the finished product can be 0.2 to about 2%, depending on the duration of fermentation.
At lower temperatures between 8 and 18 ° C, yeast fermentation predominates and the product is milder because it contains less lactic acid. The content of carbon dioxide and ethanol , however, is higher. If the vessel is hermetically sealed and the carbon dioxide content increases as a result, the yeast growth will be impaired.
Higher temperatures of 20 to 28 ° C prefer lactic acid fermentation by bacteria. The ethanol content is lower, the lactic acid content higher. The whey separates rather from rupture or sour milk curd , which floats above.
The kefir should ferment for at least 16 hours, but better for 24 to 36 hours.
The kefir is separated from the cauliflower-like kefir grains with a sieve while gently shaking. It is not absolutely necessary to rinse the tubers with water. However, this is recommended on occasion and will result in a slightly delayed development of the kefir.
If the tubers are not to be used again immediately, they can be covered with a water-milk mixture and stored in a cool, dark place until the next preparation. Other sources speak of storage in one percent, boiled salt water. For longer storage it is possible, under favorable circumstances, to dry the tubers, while freezing is unproblematic and only requires a certain regeneration time.
The acidic kefir can loosen metal ions from the surfaces of metal vessels. This can lead to the inhibition of the microorganisms in the kefir grains, impair the taste or be harmful to health. Therefore, only vessels and devices made of plastic, stainless steel, ceramic or glass should be used for production and, above all, storage.
The Kefirknollen ( kefir grains , Kefir , Tibetan fungus ) usually grow to about the size of walnuts, as well as fist-sized Kefirknollen are not uncommon. Kefir grains have a rubbery consistency and are made up of bacteria, yeast, proteins , lipids and polysaccharides , which are produced by various of the bacteria contained in the tubers. These tubers enlarge over time and partially disintegrate into smaller tubers. They double their mass at room temperature in about 14 days. Kefir grains can be dried or frozen for storage.
In health food stores and pharmacies, kefir ferment is available in the form of an almost anhydrous, granular powder, which can be kept for months in unopened packaging. The application is straightforward. According to the instructions on the packaging, the batch can usually be extended 40–50 times before another batch with kefir ferment should be made. When using kefir ferment, no kefir grains form.
Industrially produced and commercially available kefir usually does not correspond to the drink traditionally made with kefir grains and is called "kefir, mild". To ensure that the resulting drink always tastes the same, a defined mixture of different bacteria and yeasts is used industrially, which cannot completely imitate the complex composition of the microorganism consortium of kefir grains. Traditional kefir is composed differently depending on the region and the season. “Kefir, mild” usually contains hardly any alcohol, but still approx. 2.7–3.9 g lactose per 100 g and is therefore not suitable for people with lactose intolerance. The real kefir contains more alcohol in comparison, but is largely lactose-free.
Cream kefir is usually made from this kefir with a fruit preparation without lactose-fermenting yeast. It has a slightly thinner consistency than cream yoghurt and contains around 10% fat in the milk.
The frequently encountered statement about the allegedly life-prolonging effect of kefir goes back to a probiotic publication by the Russian bacteriologist Ilya Ilyich Metschnikow from 1908. In it he had established a connection between the relatively old age of Romanians and Bulgarians and their regular consumption of sour milk. Since this publication dates from 1908, in which Metschnikow was awarded the Nobel Prize, it was noted by a broader public. Since then, kefir has often been examined for its health effects. Kefir has the ability to suppress pathogenic microorganisms. For example, Listeria are reduced by around 90% within 24 hours. Fermented dairy products also stay longer in the intestine than pure milk, which may contribute to better digestibility.
- Lactic acid bacteria such as Lactobacillus acidophilus , Bifidobacterium bifidum , Streptococcus thermophilus , Lactobacillus delbrueckii subsp. bulgaricus , Lactobacillus helveticus , Lactobacillus kefiranofaciens , Lactococcus lactis and Leuconostoc in concentrations of around one million to one billion colony-forming units per milliliter.
- Acetic acid bacteria
- Yeasts that can process lactose: Kluyveromyces marxianus , Kluyveromyces lactis and Saccharomyces fragilis
- Yeasts that cannot process lactose: Saccharomyces cerevisiae , Torulaspora delbrueckii , and Kazachstania unispora .
- Fermentation products: lactic acid , carbonic acid , carbon dioxide , ethanol (alcohol)
- Nutrients: Polysaccharides (multiple sugars) such as kefiran (a metabolic product of lactic acid bacteria).
- Vitamins or vitamin precursors: vitamin A , vitamin B1 , vitamin B2 , vitamin B6 , vitamin B12 , vitamin D , folic acid , niacin
- Minerals: calcium , iron , iodine , magnesium
- balanced amino acid profile (from goat milk e.g. glutamic acid, tryptophan + valine, leucine and lysine)
The milk sugar (lactose) contained in milk is first converted by lactic acid bacteria into lactic acid, by propionibacteria into propionic acid and by other bacteria into acetic acid , diacetyl , citric acid , pyruvic acid , acetoin , acetaldehyde and amino acids , which contribute to the characteristic taste of the kefir.
Eventually, the remaining lactose is mostly converted to alcohol and carbon dioxide by the slower yeasts. Due to the low residual lactose content, kefir can be consumed by most people with lactose intolerance , just like yoghurt , buttermilk and sour milk .
According to Russian legends, Muhammad showed Orthodox believers in the Caucasus how kefir is made.
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