Fermented drinks
Kombucha, kefir and kvass are gaining popularity worldwide. However, their impact on health has yet to be confirmed.
Kvass is made by fermenting rye bread, and is very popular in Russia. ©Shutterstock/Davidchuk Alexey
The fruity, tangy flavour and slight fizz of Kombucha is making it more and more popular. This fermented black tea originated in the Far East,1 and supposedly heals countless ills, from acne to digestive problems or cancer. Consumers are putting their faith in it to such an extent that, according to the most recent figures from Markets and Markets,2 the global market is expected to reach 1.8 billion US dollars in 2020 (compared to 0.6 billion in 2015).
Kefir has similar therapeutic attributes. It is a slightly sweet and tart yoghurt drink produced by fermenting milk.3 It originally came from the Caucasus and is particularly popular in Russia and northern Europe. Kvass, also known as ‘bread beer’, is lesser known than kombucha and kefir. It is made by fermenting rye bread, and is one of the most frequently consumed drinks in Russia.4
When chemistry is involved
Whatever their history, these beverages owe their recent popularity to fermentation, a natural process known for some 12 000 years.5 Bacteria and yeast are microorganisms that bring about a natural chemical reaction. When deprived of air and immersed in liquid at room temperature, bacteria transform the sugars in food into acids, while yeasts convert sugars into alcohol or carbon dioxide. The result is that kombucha, kefir and kvass have a sour taste, are lightly sparkling and sometimes contain a little alcohol.
When making kombucha, a white, viscous membrane called the ‘mother kombucha’ is added to sweet black tea and this triggers fermentation. Although the mother kombucha is akin to a fungus, it is actually a bacteria and yeast culture known by the acronym SCOBY, which stands for Symbiotic Culture of Bacteria and Yeast. When the microorganisms that make up the SCOBY come into contact with the liquid, they proliferate and convert the sugars in the tea. After fermentation, which can take from one to two weeks, the mother kombucha is removed, the liquid is filtered and the drink is ready to consume.
As Jenny Neikell explains in her 2016 book Les bienfaits de la fermentation6 (The benefits of fermentation) the same principle applies to the preparation of kefir. However, in this process, the viscous membrane is replaced by kefir grains, which look rather similar to small white cauliflowers and which release yeast and bacteria when in contact with milk. The kefir is considered ready when these grains float to the surface. As for kvass, the rye bread should be toasted before being soaked in water mixed with sugar, yeast and various herbs.
Source of probiotics
Although bacteria and yeasts are often thought to be bad for you, most of them are actually harmless. In fact, many types of bacteria and yeasts are actually essential to ensure that our bodies function correctly. Such bacteria and yeasts are known as probiotics.7
Probiotics are naturally present in our intestinal flora – or intestinal microbiota – and produce the enzymes needed to break down and digest the food we eat, while also providing nutrients such as vitamin K, certain B vitamins and minerals. The fact that they are in the intestine actually stops harmful bacteria and yeasts forming there.
In this search for balance, fermented drinks seem to be valuable allies, as the bacteria and yeasts activated by the fermentation process are also probiotic. Embryette Hyde, project manager of the American Gut Project8 notes that, “These beverages are said to act like a form of pre-digestion.”
Transforming sugars makes fermented drinks acidic, which in turn creates a hostile environment for certain harmful agents and means that good bacteria and yeasts are able to multiply. Since the microorganisms have already broken down the sugars, this makes kombucha, kefir and kvass easier to digest. Moreover, the enzymes produced by bacteria and yeasts transform lipids into fatty acids, proteins into amino acids, and complex carbohydrates into simpler carbohydrates.
Debatable benefits
Despite this acknowledged benefit to digestion, scientists remain cautious about any of the other purported merits of these products. Embryette Hyde points out that, “Consuming fermented food increases the diversity of microorganisms found in our intestinal flora, but it is still hard to identify the precise effects on the microbiota. Further studies are necessary.”
According to Aristea Baschali,9 “The benefits credited to these drinks are mostly based on testimonies of personal experience.” She adds that, “At present, scientific studies have focused on kombucha and kefir, but the impact of these drinks on health has yet to be proven.”
This is an opinion shared by Waisundata Yashasvi Viduranga,10 Research Fellow at the Faculty of Applied Sciences at the Rajarata University of Sri Lanka: “Like all ‘probiotic’ products available on the market, these drinks can have an effect on your intestinal flora. However, they are not medicines. How effective they are depends on the composition of the ferment. In the case of kombucha, some SCOBYs are richer in probiotics than others.” According to the United Nations Food and Agriculture Organization, probiotics are only beneficial if they are consumed in sufficient quantities.11 Furthermore, there are several strains of probiotics, some more effective than others. There is no indication that a bottle of kefir, kvass or kombucha contains either the right strains, or in the right quantity.12
Kefir and kombucha have been accused of being toxic. Aristea Baschali explains that, “In the case of kefir, some studies have shown the presence of biogenic amines. If these are consumed in large quantities, they could be a health risk, especially to a weak immune system. For kombucha, over-consumption can cause some people to experience stomach ache, or even metabolic acidosis, meaning a high level of acid in the blood.”
In 1995, following two reported cases of kombucha poisoning, the US Food and Drug Administration recommended that people with a weakened immune system should not consume kombucha.13 Doctors in Los Angeles repeated this advice in 2009 when a young, HIV-positive man suffered from kombucha poisoning.14
However, the drinks are not to blame. Embryette Hyde says that, “They may magnify symptoms in particular individuals at risk, but they are not toxic in themselves.” Waisundata Yashasvi Viduranga confirms that, “As with all foodstuffs, they must be consumed as part of a balanced diet. The risks begin with excessive consumption.”
Glossary
Microorganisms
Microscopic living creatures found in the human body, in food and in the environment. There are countless types of microorganisms, but those active in the fermentation of foodstuffs are bacteria, yeasts and fungi.
Probiotics
These are harmless living microorganisms, mainly bacteria belonging to the genera Lactobacillus, Bifidobacterium and Streptococcus, and Saccharomyces boulardii yeasts. They are naturally present in our intestinal flora, but may also be found in some foodstuffs and food supplements.
Intestinal flora
This refers to the billions of microorganisms that live along the digestive tract. Today, it is more common to speak of intestinal microbiota.
Vitamin B
The B vitamins produced by probiotics are vitamin B2, which acts on the hormonal system, and vitamin B12, which acts on the nervous system and is important in the production of red blood cells.
Vitamin K
The K vitamins produced by probiotics are vitamin K1, which affects blood coagulation and vitamin K2, which is reputed to have anticancer properties. It also helps fix calcium on bones, preventing it from blocking arteries.
Biogenic amines
These molecules originate when amino acids are degraded and so indicate the freshness of food. During the fermentation process, microorganisms break down proteins to make amino acids, which are easier for the body to assimilate. These may in turn be converted into biogenic amines. The best known is histamine, but there are many more, such as tyramide, putrescine, cadaverine and spermidine.
Glossary
Microorganisms
Microscopic living creatures found in the human body, in food and in the environment. There are countless types of microorganisms, but those active in the fermentation of foodstuffs are bacteria, yeasts and fungi.
Probiotics
These are harmless living microorganisms, mainly bacteria belonging to the genera Lactobacillus, Bifidobacterium and Streptococcus, and Saccharomyces boulardii yeasts. They are naturally present in our intestinal flora, but may also be found in some foodstuffs and food supplements.
Intestinal flora
This refers to the billions of microorganisms that live along the digestive tract. Today, it is more common to speak of intestinal microbiota.
Vitamin B
The B vitamins produced by probiotics are vitamin B2, which acts on the hormonal system, and vitamin B12, which acts on the nervous system and is important in the production of red blood cells.
Vitamin K
The K vitamins produced by probiotics are vitamin K1, which affects blood coagulation and vitamin K2, which is reputed to have anticancer properties. It also helps fix calcium on bones, preventing it from blocking arteries.
Biogenic amines
These molecules originate when amino acids are degraded and so indicate the freshness of food. During the fermentation process, microorganisms break down proteins to make amino acids, which are easier for the body to assimilate. These may in turn be converted into biogenic amines. The best known is histamine, but there are many more, such as tyramide, putrescine, cadaverine and spermidine.
