Kefir is a fermented milk drink similar to yogurt, but more liquid and acidic. This probiotic drink has great health benefits, as well as being safe, inexpensive and very easy to make at home. 

Milk kefir

Milk kefir is a drink resulting from the fermentation of milk with granule-shaped microorganisms, called Bulgarians, which mainly contain yeasts, bifidobacteria, lactic acid bacteria and acetic acid bacteria.

These microorganisms feed on the sugar in milk (lactose) to convert it into lactic acid, carbon dioxide and alcohol.

Milk kefir has a very low alcohol content, usually between 0.08% and 1%.

The result of the fermentation is kefried milk, a slightly more acidic and liquid drink than yogurt, with a low sugar (lactose) content and probiotic, which provides us with minerals, vitamins, essential amino acids and easily digestible proteins. In addition it has medicinal properties, all of them discussed in this article. 

To learn more about what and how to ferment at home, check out A Beginner's Guide for Home fermentation article.

Composition

The nutritional composition of kefir varies depending on the composition of the milk, the origin and composition of the granules, the fermentation time and temperature and the storage conditions. Generalizing, kefried milk contains:

• Between 80 and 90% water, between 0.2% and 3.5% fat, 3% protein, 6% sugar, 0.7% ash and approximately 1% lactic acid and alcohol. 
• The essential amino acids produced in the fermentation for 100 gr of kefirized milk are: lysine (376 mg), isoleucine (262 mg), phenylalanine (231 mg), valine (220 mg), threonine (183 mg) , methionine (137 mg) and tryptophan (70 mg).
• It contains vitamins B1, B2, B5, C, A, K and carotene, in addition, the fermentation process increases the concentration of pyridoxine (B6), vitamin B12, folic acid, biotin, thiamine (B1) and riboflavin (B2).
• It is a good source of minerals, it contains magnesium, calcium, phosphorus, zinc, copper, manganese, iron, cobalt and molybdenum.
• It also contains and modulates other substances, which we will see below and which you can expand on in the sources.

Multifunctional Drink

The name kefir comes from the Slavic Keif, wich means 'well-being ' or 'living well', a fact that already indicates that in ancient times its consumption was related to its health benefits. 

In addition to having the original high nutritional value of milk, kefir produces other substances during fermentation, so it provides a higher nutritional value than the milk itself. For example:

Kefiran is a polysaccharide that surrounds kefir grains with antitumor, wound healing and antimicrobial properties against some bacteria and Candida albicans.

Much of the studies on kefir have been done on mice, rabbits, and even flies! So clinical studies are still needed to better understand the effects of regular kefir use on disease prevention. 

This are some of the medicinal properties of milk kefir, already studied:

• Antioxidant: At fermentation, peptides and exopolysaccharides (kefiran) are released, both with antioxidant properties. 
• Antihypertensive: This metabolites also has antihypertensive activity and prevent cardiovascular diseases.
• Hypocholesterolemic: In rabbits and mice, has been seen a reduction in cholesterol caused by the consumption of lactic acid bacteria, but studies in people have not given the same result, it may be because humans need a very high concentration of BAL. 
• Antimicrobial: due to the acidity of the fermentation, the slight alcohol content and the antimicrobial activity of some bacteria present in kefir. Several studies show that milk kefir has antimicrobial activity against:
  • Bacterias: Staphylococcus aureus, Bacillus thuringiensis, Escherichia coli, Salmonella enterica y Shigella dysenteriae.
  • Fungi: Aspergillus niger, A. flavus, Rhizopus nigricans and Penicilliun glaucum. 
  • Helps reduce some syntomes caused by H. pylori.
  • It prevents diarrhea or enterocolitis caused by Clostridium difficile.
• Anti-inflammatory and anti- allergenic: Studies in animals have detected an increase in immunoglobulins (antibodies that contribute to immunity), the inhibition of the increase in inflammatory cells in asthmatics and a decrease in pro-inflammatory cytokines together with an increase in anti-inflammatory ones.
• Antitumor: Although these mechanisms are not yet known, it has demonstrated antitumor activity against several types of cancer cells, it is assumed that it is produced by its immunostimulating, probiotic effect and because what is already commented about cytokines. 
• Other studies show:
  • Improves bone composition, reducing the risk of osteoporosis.
  • Results comparable to some antiulcer drugs used in stomach ulcers.
  • Reduces colon and intestinal bleeding.
  • It benefits the digestion of proteins and reduces the glycemic index, due to its hypoglycemic and intestinal enzymatic activity.
  • Less progression of diabetes due to the improvement of blood sugar levels, caused by its probiotic properties, which reduce intestinal permeability, oxidative stress and inflammation.

In a clinical study, diabetic adults who consumed 600 ml of kefir per day for 8 weeks showed a significant decrease in fasting glucose and glycosylated Hb levels compared to the initial values.

• Antiviral: The consumption of kefir has reported activity against the Zika virus, HCV, hepatitis B virus, influenza virus (H1N1), HSV, rhinovirus and retrovirus.
• Coronavirus: Recent studies show that kefir and its derivatives (polysaccharides, proteins, peptides, among others) can suppress viral activity due to their action on the immune system. It could also significantly inhibit the 'cytokine storm' that contributes to COVID-19. The replication of SARS CoV-2 is pH dependent and consuming kefir change the pH in a specific area. Obviously, these facts are under study.

Making kefir at home

To start making milk kefir you need the Bulgarians or granules, which are the culture of yeast and bacteria. This culture is granular, whitish in shape and fluffy in texture. To get them, look for exchange communities in your area or on the internet.

When you have the Bulgarians, add them to an animal milk so that they feed on lactose in a proportion of 1 to 3 tablespoons of Bulgarians per liter (0,26 Gallon) of milk. You can use pasteurized whole, semi-skimmed, or skimmed milk from cow, goat, sheep, camel or buffalo.

The among of Bulgarian to milk ratio is variable, orient yourself with a tablespoon of grains per milk liter (0,26 Gallon) and depending on the time it takes to ferment and your desire to consume it, increase or decrease the amount of milk. 

By adding microorganisms to pasteurized milk, you transform a dead food into alive food. 

Leave the milk with the Bulgarians in a glass jar covered with a cloth and a cord, so that the CO2 can be released, for 18 to 24 hours at 20-25°C (69 to 77 ºF). Fermentation of milk kefir occurs at temperatures ranging between 8 and 25 ºC (46 to 77 ºF) and can last from 10 to 40 hours.

You will know that your kefir is ready to consume because the fat part of the milk starts to curdle due to the acidity produced during fermentation and is separated from the whey. If you want to know more about how and why milk curdles, you have the info at the aticle: Ways to curdle milk.

When it ferments too long, a curd forms floating in whey. Then you can separate the curd from the whey and the grains of kefir, salt it and make spreadable cheese, optionally spiced to your liking.

If the taste is too acidic, try to ferment for less time in the next batch. 

Once fermented, strain the milk to separate the Bulgarian grains and start another batch with them. Using a non-metallic strainer is recommended, as non stainless steel metals react with the acidity of kefried milk, but you can use metal tools if it is only for a moment.

You can store your kefried milk or drink it. If you let it at room temperature it will continue to acidify even if it does not contain the granules. When we let it cool in the fridge there is an accumulation of CO 2, ethanol and vitamin B complex that is favorable for people with lactose intolerance or diabetes.

How is it taken?

Of many ways! You can consume it like yogurt, alone or adding honey, jams, cereals... You can use it in desserts, cakes or pies in place of yogurt or make cheese cream and fresh cheese by separating the whey. You can also make sauces like Tzatziki, or modify them and improvise!

Our latest discovery is the cream of kefir and cucumber, with garlic, parsley, salt, pepper and some extra virgin olive oil...

We use milk kefir to protect raw milk with which we make goat cheeses. If you want to apply this method to your cheeses, we will tell you about it in the article Kefir cultured raw milk on cheesemaking

Keep in mind that probiotics die by cooking the kefir, and when it is kept below 15ºC (in the fridge) or above 30ºC, its probiotic power decreases.

Tricks and myths about kefir:

• You cannot create your own granules at home. Thousands of years ago, kefir was naturally created in animal stomachs used to store milk in the Caucasus and Tibet region. Reproducing those same conditions is now impossible. You must find the granules to get started.
• The microorganisms in kefir feed on lactose, which is the sugar in animal milk. If you want to make kefir with vegetable milk, these microorganisms will starve. Even so, you can occasionally ferment kefir in non animal milk, but you should make several previous and nexts batches with animal milk to avoid overly weakening the microorganisms. 
• There is also water kefir, but although they bear the same name, they are different microorganisms; they feed differently and they are not interchangeable. Do not feed your water kefir with milk or vice versa! Water kefir is a probiotic and bubbly drink indicated for vegans, lactose intolerant and allergic to milk products. 
• If you want to stop producing kefir, you can dry and freeze the granules. When you want to start over the fermentation, do it normally but discard the first 3 or 4 batches of kefried milk, so that the microorganisms gain strength, the fermentation stabilizes and the final product is healthy. 
• You can buy kefir milk instead of making it yourself, but the industry uses isolated microorganisms produced in laboratories to ferment the milk, so kefir milk from the supermarket contains a smaller amount and variety of microorganisms compared to kefir produced from the traditional and homemade way. It is also much cheaper to do it yourself. 
• To prepare the next batch you could wash the Bulgarians with non-chlorinated water or fresh milk or not wash them. Today you have learned about kefiran, if you wash the granules you will eliminate this substance, so you will decrease its properties and its growth. 
• The granules grow slowly, if you see that your granules do not grow well, check the temperatures and times at which you ferment it, change the milk and do not forget to collect the minigranules that remain in the strainer. If you see that your granules begin to reduce, check the entire process very well. Granules that starve for a long time may disappear. 

Sources consulted:

• Rodríguez-Figueroa, José Carlos; Noriega-Rodríguez, Juan Antonio; Lucero-Acuña, Armando; Tejeda-Mansir, Armando. Advances in the study of the multifunctional bioactivity of kefir Interciencia , vol. 42, no. 6, June, 2017, pp. 347-354 Interciencia Association Caracas, Venezuela. [ Link ]

• Olivo, Diana & Galván, Marcos & López-Rodríguez, Guadalupe & Suárez-Diéguez, Teodoro & González-Unzaga, Marco & Anaya-Cisneros, Lizbeth & López-Piña, Dulce. (2017). Biological activity and therapeutic potential of probiotics and kefiran from the kefir grain . Ibero-American Journal of Sciences. 4. 49-56. [ Link ]

• Reham Samir Hamida, Ashwag Shami, Mohamed Abdelaal Ali, Zakiah Nasser Almohawes, Afrah E. Mohammed, Mashael Mohammed Bin-Meferij. Kefir: A protective dietary supplementation against viral infection, Biomedicine & Pharmacotherapy, Volume 133, 2021. [Link]

• Rosa, D., Dias, M., Grześkowiak, Ł, Reis, S., Conceição, L., & Peluzio, M. (2017). Milk kefir: Nutritional, microbiological and health benefits. Nutrition Research Reviews, 30(1), 82-96. doi:10.1017/S0954422416000275 [Link]