Kombu-WHAT ?
All you need to know about this trendy fermented drink
Chances are you’ve heard of kombucha before and maybe have even had a taste of this strange drink, but what it really is and what benefits it holds still remain a mystery to you. This is why I scouted scientific reviews and wrote this.
What is kombucha?
Kombucha is a mildly sweet and acidic, slightly carbonated, fermented tea historically consumed in China since 220 BC. It crossed over two Millennia of human history because of long-held beliefs in its health benefits. The drink migrated to Russia, Germany, Europe, Americas, and in the past few years became popular worldwide. Indeed, it is currently the fastest-growing product in the functional beverage market, driven by the demand for authentic, natural, fermented, healthy drinks with low sugar and alternatives to soft drinks and alcoholic beverages, especially among Millennials. In 2020, according to Lumina Intelligence, there were 207 kombucha brand variants in 25 countries, over a quarter of which in the US. Also called Tea Fungus, Kargasok Tea, Manchurian mushroom, and Haipao, it contains nutritionally-interesting organic acids, vitamins, minerals, and phenolic compounds.
What is kombucha’s microbial composition?
To make kombucha, you just need tea and sugar, and what is called a SCOBY, which stands for Symbiotic Cultures Of Bacteria and Yeasts. The SCOBY is a gelatinous, cellulose-rich mattress of several layers of bacteria and yeasts floating at the surface, and is considered the kombucha mother.
The bacterial species in SCOBY are mostly acetic acid and gluconic acid species, with Acetobacter xylinum as the primary species — the mother of vinegar, followed by Acetobacter aceti, pasteurianus, and Gluconobacter oxydans (Greenwalt et al., 2000, Kapp et al., 2018).
The composition in yeasts is more variable, the most frequent are Brettanomyces, Zygosaccharomyces, Saccharomyces, including famous S. cerevisiae, the beer yeast, Torulopsis sp. and Pichia sp (Greenwalt et al., 2000, Kapp et al., 2018). Apparently, SCOBYs in different countries are based on different types of yeasts.
What goes on inside?
What happens during fermentation is a conversion of sugar into glucose, fructose, and ethanol, transformed by the bacteria into gluconic acid, glucuronic acid, and acetic acid (yes, it’s pretty acidic if you leave it to ferment too long). Bacteria transform ethanol into acetic acid, the food of the yeasts, and as the yeasts grow and die, their components support the development of bacteria. The yeast’s production of ethanol assists the bacterial production of acetic acid. This is why kombucha is a perfect example of symbiosis. See the illustration below — in blue, the ingredients consumed in the fermentation, in brown and beige, the microbes at play, and in green, the main products of this fermentation.
After fermentation, kombucha contains sugars, tea polyphenols, organic food acids, fiber, ethanol, amino acids, minerals such as copper, iron, manganese, nickel, and zinc, vitamins such as vitamin C and group B vitamins, carbon dioxide giving the drink its nice frizziness, antibiotic substances and hydrolytic enzymes (Kapp et al., 2018).
The content in metabolites, the products of fermentation, is directly related to the amount of sugar used. The production of ethanol is normally kept in check by the balance between the yeasts and acetic acid bacteria. As for non-alcoholic beverages, the legal limit is 0.5 %. However, the ethanol content has been found in higher amounts, and not labeled, notably because, after the bottling, the increase in carbon dioxide impedes acetic acid bacteria to consume the ethanol so it can increase post-release analyses — although refrigeration stabilizes it (Ferreira de Miranda et al., 2022).
What about the benefits?
As a kombucha consumer, I set out in this investigation to find out if the literature supports the benefits commonly attributed to kombucha in immunity, liver health, cancer, detox, etc. I imagine this is also what you are most interested in finding out. It’s not black or white, as you’ll see.
The long history of consumption and the migration of the drink onto all continents is due to the faith in its benefits. In Russia, kombucha is consumed against metabolic diseases, hemorrhoids and rheumatism. Epidemiology studies report lower rates of cancer in the regions drinking it (Greenwalt et al., 2000). A lot of benefits have been attributed to kombucha, but how much is actually supported by science?
Protective properties can be expected from the presence of organic acids and phenolic compounds. Vitamins could bring antioxidant properties, possibly associated with reduced complications related to diabetes and cancer (Ferreira de Miranda et al., 2022). In rats, the consumption of lyophilized kombucha effectively reduced HbA1C, a marker of diabetes (Srihari et al., 2013). Antiproliferative activity of cancer cells was also tested in different cellular models (Ferreira de Miranda, 2022, Srihari et al., 2013)
Because tea is rich in polyphenols including catechins and tannins, which could be enhanced after the fermentation, kombucha could bring benefits such as antimicrobial activity against common pathogens (Battikh et al., 2012), cardioprotective and antidiabetic (Aloulou et al., 2012), and antiobesity effects (Ferreira de Miranda et al., 2022). One study in 24 human subjects with non-insulin-dependent diabetes reported that consumption of 60 mL per day for 90 days improved blood sugar values, but it didn’t have a control group (Kapp et al. 2018).
Wang et al. also reported some benefits of kombucha on the liver in 2013, while highlighting that such merits can be strain-specific.
Steinkraus et al. (1996) tested the antibiotic activity of kombucha and found it to antagonize H. pylori, E. coli, Staph. aureus, Agrobacterium tumefaciens and B. cereus. The authors suggest that SCOBY could even be used topically to reduce dermal injuries and burns, although no human trial confirms it to work.
As you can see, these touted benefits are only backed by in vitro models, a few rat studies, and a small human pilot study conducted 20 years ago in India without a point of comparison. I could have missed something, but the review by Ferreira De Miranda is thorough and published in 2022, so it looks like this is where we stand. The expectation of benefits is mostly associated with the commonly found ingredients in the beverage, but not confirmed for the finished product.
Are there risks?
The review by Greenwalt describes internal lesions in rats after 12 weeks of consumption, and a case of a man’s death in America in 1995, from the perforation of the intestinal tract and severe acidosis. The man’s consumption appeared to be quantitatively and qualitatively inappropriate (too acidic). The investigation concluded that a consumption of 4 ounces per day in a healthy population is not harmful, but that there are risks in cases of excessive consumption associated with preexisting health problems.
According to the CDC, there are no risks for a healthy population to consume 110 mL/day, but there could be risks for higher consumption and immunocompromised patients.
Ferreira de Miranda also highlights counter-indications in pregnant women and infants, children below 4 years old, patients with kidney failure, and HIV patients.
Kapp et al. describe different types of side effects related to kombucha drinking: hyponatremia (low level of sodium in the blood), lactic acidosis, toxic hepatitis, hyperthermia & renal failure, myositis, and pellagra.
Risks could also be linked to the growth of pathogens in the non-sterile kombucha environment. Its acidity is protective against the contamination of most pathogens, but mycotoxigenic molds could grow at pH 2.5 and generate toxic secondary metabolites (Greenwalt et al.). Cases of contamination have also been observed with penicillium and Candida.
In general, it is safe to make at home, if correctly prepared, although “correctly” is not properly detailed by Greenwalt or Mayser, which it quotes.
Does kombucha contain probiotics?
Most people understand that kombucha contains bacteria and assume it is full of probiotics. Que Nenni!
To qualify as probiotics, microorganisms must meet well-defined criteria:
- be characterized down to the strain level (meaning the code following its Latin name)
- be safe for intended use
- exert a health benefit demonstrated in at least one positive human study, or belong to species with a recognized benefit shared across the species
- deliver the viable efficacious dose until the end of shelf life
With kombucha cultures being different from home to home and brand to brand, and usually failing to label even at the species level, it will be a struggle to develop kombucha-based products as real probiotics. However, in the US in particular, the claim “probiotic” can be found on many products that do not meet these criteria. For more details about the difference between probiotics, fermented foods, and dietary microbes, you can refer to this previous article.
How to make kombucha?
First, you need the SCOBY, and ideally a small amount of liquid kombucha, as an inoculum. You can find the SCOBY online, and try social media and forums to find some for free — once you brew kombucha regularly, you have SCOBY to give away every month or so. If you’re in Paris or around, contact me.
Once you have your SCOBY, here’s the very simple recipe I use, which provides 2 liters per week:
- 2 L water, 1L boiled and 1 L poured in cold
- 6 spoons of black tea (about 12 g) and 2 spoons of green tea (about 4g), organic
- 150 g sugar (white — I first used raw sugar for its minerals and nutrients, but the cultures won’t access the sugar molecules as easily and it impedes the carbonation process)
Leave the tea to infuse until it is cold enough to put your (perfectly cleaned) hands in, and sift the liquid into your brewing fountain. It’s convenient to have a little tap to try your kombucha regularly and find the perfect spot between sweetness and acidity that fits your taste. I use one like this:
Unscrew the tap and replace it with a clean cloth, well-attached with rubber bands to prevent flies and dust to come into your kombucha, place the SCOBY on top, and leave it to do its magic. After about a week, depending on the temperature, you have kombucha. You can then transfer the golden liquid to a tightly-closing bottle, leaving just a few centimeters in the bottom of the fountain to keep the SCOBY hydrated and happy. Replace, in the brewing fountain, with a new batch. Leave the bottles in the fridge for a day or two to stimulate carbonation, and enjoy fresh. It can be consumed as is, or if too acidic, with a little syrup, and there are many flavoring variants you can try to your taste. For example, fruit juices, ginger and spices add a zing to your kombucha. In Asia, trendy flavors include Chrysanthemum & Goji berry, Apple & Ginger, Passionfruit, Mint Lime Nojito… (NutraIngredients Asia). You can also variate the tea you use, including black, green, white, red teas, and even herbal infusions.
Other variants exist, called kombucha analogs, fermenting other substrates than tea, such as thyme, rosemary, fennel, and mint infusions.
If your kombucha has gone way too acidic, you can use it as vinegar!
Conclusion
The demonstration of kombucha benefits is scientifically weak, which does not mean that it isn’t healthy, but consumers and professionals should be aware of the low level of evidence and the existing risks. It will be tough for the scientific community to build a case and clarify which composition, dosage, frequency, and duration of kombucha consumption brings benefits, and to which populations, given the high variability of recipes. A better understanding of the mechanisms of action, as in the probiotics field, will be crucial to enhance producing or buying habits.
In the meantime, kombucha can be part of a healthy diet when prepared adequately, consumed in appropriate amounts, and expectations kept realistic — especially if it replaces beer or sugar-dense soft drinks.
You just read another post from In Fitness And In Health: a health and fitness community dedicated to sharing knowledge, lessons, and suggestions to living happier, healthier lives.
If you’d like to join our newsletter and receive more stories like this one, tap here.
