Microbes In Food Kombucha: The Fermented Drink You Can Easily Create At Home
Updated: Nov 28, 2020
In our time of quarantine people, perhaps even you, have turned to the comfort of baking bread to ease stress. But as the summer heat settles in, hours of baking can uncomfortably raise the temperature of your house. Fret not, though, my microbial bakers, there are other fermented foods that can de-stress and refresh in the times of heat and quarantine.
Photos credit: Christopher Drozd
Three quick fun facts about Kombucha!
Fact 1: Personal testimonies (not science!) claim this magical elixir has the ability to cure every ailment from improving your liver, immune system, gastric function to increase vitality, and curing AIDS and cancer. A true “Snake oil”.
Fact 2: Kombucha has been around for thousands of years with origins likely stemming from China as far back as 220 B.C.
Fact 3: It's also known as: Cainii grib, Fungus japonicus, Cembuya orientalist, Tschambucco, Volga spring, Mo-Gu, Champignon de longue vie, Teekwass, Kwassan, Kargasok tea, Cainii kvass, Japonski Grib, Heldenpilz or Jsa Kvaska.
Kombucha is a fermented tea, created through an intricate series of interactions between both bacteria and yeasts. Kombucha is created by dissolving sugar into boiling water and steeping tea leaves (either green, black or blue [oolong] ) for a short time.
Microbes are added once the tea is at room temperature; too hot and they die. Microbes can be inoculated (fancy science word for added) into the tea in one of two ways.
The first is the brewer adds a small piece of SCOBY the second being a small portion of the last fermented tea product. This is known as back-slopping. It is common practice in many microbial fermented foods such as sourdough, fermented meats, cereals, yogurt and kefir.
A cloth is usually placed on top of the container at this time and the mixture is allowed to sit (ferment) at room temperature for 8-14 days. The cloth allows for aerobic (oxygen) conditions while excluding pesky insects and other intruders. Anaerobic (without oxygen) can drastically change the microbial profile. Leaving you with an undrinkable tea.
There has been a surge of consumer interest in this product creating more interest by the scientific community to study it. Go consumer demand! The increasing demand has, in today's market, increased variety where we can now find everything from fruity to alcoholic kombucha products.
Kombucha may have some other uses as well outside of being a magical elixir. Kalaiappan and colleagues manipulated the SCOBY to create activated carbon. This combined with sulfur, graphene oxide, polyacrylonitrile, at just the right conditions produces a composite cathode. Which may have used in future lithium-sulfur batteries. But that's a little beyond the scope of this post.
So.....what's a SCOBY?
A SCOBY is a zoogleal mass of microbes. It stands for symbiotic culture of bacteria and yeast. Because Kombucha has been home-brewed for thousands of years, the microbial diversity is quite expansive. It can be rather diverse or simplistic depending on where, when, and who created it.
Bacteria that produce acetic acid are common in all brews, are also used in cocoa bean fermentation and wine, and are rod-shaped (1-4um long). The most common genera found in Kombucha are Gluconobacter, Gluconacetobacter, and Komagataeibacter.
Arikan and colleagues looked at the microbial profile of two Turkish Kombuchas to see if the profile changed over time. To do so, they followed a very strict recipe in preparing the kombucha and sampled on days 3, 10, and 15 of the fermentation. They extracted DNA for both full genome analysis and also for amplicon (a piece of DNA) sequencing. Amplicon sequencing is a cheaper method allowing scientists to identify what the microbe is. Whole-genome analysis is more expensive but can allude to function or what the microbe is capable of.
One drawback to DNA analysis is it does not tell you if the microbe is alive or active, only if it is/was present and the functions it could perform. There are also several ways of extracting DNA. Each way will extract differently and will have biases towards certain groups of microbes. Moral of the story? Science is a balancing act between the best method and the resources available.
Anyways, methods aside, Arikan found Komagataeibacter as the dominant bacteria, comprising over 90% of the bacterial profile! Komagataeibacter, like many acetic acid bacteria, uses glucose to produce gluconic acid and ethanol to produce acetic acid. Komagataeibacter may be inhibiting the growth of pathogens, which cannot survive in acidic conditions. The acidic environment may also contribute to Kombucha's antimicrobial benefits.
Yeasts are the other microbial element in Kombucha. They are spherical and much bigger than bacteria (~8um; 2-8x bigger!). They are known for their ability to produce ethanol (alcohol) and carbon dioxide (bubbles!). In kombucha, the typical yeasts found are Saccharomyces, Zygosachharomyces, Dekker/Brettanomyces, and Pichia. In our Turkish Kombucha study, Zygosachharomyces was almost 100% of the yeast community. This yeast can convert sugars (added at the beginning of the process) to produce glucose and ethanol (used by the acetic acid bacteria).
So the yeast and bacteria are best friends sitting in this paradise you created for them, chatting it up, exchanging goods, and creating their ideal environment. They are lowing the Ph, producing vitamins, and antimicrobials so no one can disturb the little bromance they got going. They are living their best life! That is until, on one hot summer day, you crack open a bottle and imbibe their whole world.
So it goes.
Benefits of Kombucha
Scientifically, kombucha may provide mild benefits to the consumer. It is thought the low Ph probably has detoxing and antimicrobial features. Kombucha may also be a beneficial antioxidant, the caffeine in the tea can be energizing and may even stimulate your immune system. It may be beneficial to managing or preventing some diseases but certainly doesn't replace medical care.
Despite it being full of microbes that don’t harm you, Kombucha is likely not a great source of probiotics. Acetic acid bacteria are not known to provide benefits and most described to date as being probiotic belong to lactic acid bacteria. Although these microbes are found in some Kombucha, they are not ubiquitous and may not survive in storage.
So what happens then? You drink the microbes, their metabolites, the acid. Will you live forever? Have you been cured of all ailments? Of course not! But did you enjoy a nice, low-calorie refreshing beverage that might have some health benefits? You sure did! So get your ‘buch’ on and happy brewing!
Would you like to hear from a kombucha brewer? Check our interview with Christopher Drozd
Do you brew your own kombucha? What is your favorite flavor of kombucha? Tell us in a comment below!