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The Science Behind Beautiful Kombucha

Andrea Potter

Author Andrea Potter

Andrea Potter is a Chef and Registered Holistic Nutritionist, and the author of DIY Kombucha: Sparkling Homebrews Made Easy.

Since the relatively recent introduction of kombucha onto North American supermarket shelves, this healthy sparkling beverage has exploded in popularity. But can it be brewed at home, with the same tasty, healthy results? You bet! Read on to find out the science behind kombucha and the basic formula for all fermented beverages.

Excerpt from the book DIY Kombucha

Making kombucha and other fermented beverages really satisfies the culinary nerd in me. Creating tasty and inventive flavor combinations while learning more about food science and traditional cultural food and drink is what I will spend my life being fascinated with and will pass on to my daughter, so maybe she will pick up the good fermentation bug. Brewing drinks and fermenting jars of food has also inspired me to study holistic nutrition, with specific interest in how microbes affect and largely comprise personal health. I have made it part of my life’s work to understand and befriend the bacteria that support my health, as well as learning about the role of these invisible creatures in creating and maintaining cultural diversity, resulting in strong and resilient systems (both in the micro-world and in societal cultures). The added benefit of environmental sustainability and independence in doing it yourself (vs. depending on corporations to supply food sustenance) means that the practice of brewing my own fermented drinks is not just a fad; it is woven into daily routines that enrich my life on many levels and so is here to stay. Making my own fermented foods and drinks is a microcultural practice that is fortified every time I share the knowledge passed on to me, or whenever I pass along another SCOBY to a friend.

A SCOBY Hotel is a low maintenance way to store backup SCOBIES between batches.
Photo by Chris McLaughlin

A little science on basic beverage fermentation will help us get a handle on the seemingly mysterious world of bacteria and yeasts that transform sweet liquids into fizzy, tangy, healthier beverages. By understanding a little more about what’s happening in the microcosm inside your bubbling jars and bottles, you will become a better problem solver and, therefore, a more adventurous and confident brewer. While I slept through much of my chemistry class in school, when I became fascinated with the applied science of food and beverage fermentation, suddenly my interest in science was piqued. In culinary school, during salad dressings class, we were doing a vinegar tasting. An innocuous question sparked my quest to understand more about microbes: “But where does vinegar come from? How is it made?” My question stumped the instructor. “Well, err, it is just wine, or apple juice that is left out and goes sour . . .?” So my query left me sifting through chemistry formulas, starting with carbohydrates and ending up with acids.

But how? Who or what was responsible for the conversion of sugar to vinegar? The next step led me from chemistry to biology books, learning about yeast and bacterial fermentation. I am by no measure a food scientist, but getting a handle on the basic science of fermentation in food and drinks helped me understand food safety, troubleshoot a gushing or burst bottle, a soda that didn’t fizz, and get to the bottom of why one batch went differently than planned while the next was tasty. I appreciate this straightforward definition of fermentation by Sandor Katz, author of Wild Fermentation and The Art of Fermentation: “Fermentation = the transformative action of micro-organisms.” .

Root-Beer, fermented with a ginger bug culture.
Photo by Chris McLaughlin

This simple definition reminds me that fermentation is all around us! It is what turns milk into yogurt, transforms flour and water into delicious sourdough bread, puts bubbles and alcohol into malted barley water to make beer, and makes sweetened tea into fizzy, sour kombucha. Fermentation is responsible for the transformation of flavors, textures, and nutrition of many of the foods and drinks we love. We are innately attracted to foods and drinks that have benefitted from the transformative process that is fermentation. As you can see, fermentation produces a wide variety of different outcomes, depending on:

  1. the medium (contents of the food or drink being fermented);
  2. time (how long it was cultured for); and
  3. the conditions it was cultured in (like temperature, humidity, access to oxygen, etc.).

People spend their lifetimes becoming craft makers of just one or a few of these foods or drinks, perfecting their methods as they learn the intricacies of the specific culture(s) at work. While I admire that people dedicate their lives to becoming experts at a narrow scope of fermented beverages or foods, do not let this discourage you from trying your hand at it. Carrying on the craft of fermenting beverages can easily be incorporated into home kitchen routines; in fact the realm of beverage fermentation has roots in home kitchens all over the world; it was first the domain of amateur cooks, with access only to basic equipment, handed-down recipes and cultures, and hands-on learning. In this book, you’ll learn about basic beverage fermentation, with a focus on low alcohol drinks. These are projects that are right at home on any kitchen countertop or tucked away into an airy pantry.

The author enjoys some Root Beer, fermented using a ginger bug
Photo by Chris McLaughlin-

The basic formula for fermented beverages is as follows

Water + sugar + micro-organisms (bacteria and/or yeasts and sometimes even mold)


Alcohol production, reduced sugar content, carbon dioxide, production of organic acids, increased enzyme activity, increased bacteria counts and production of B vitamins.

These are the key factors that contribute to how much of each product of fermentation that you get:

  1. Time
  2. Temperature
  3. Type of organism (culture[s]) introduced
  4. Amount of available sugar

Two examples:

  1. A yeast-dominant culture at higher temperatures with high sugar content will result in higher alcohol and carbon dioxide production.
  2. Bacteria-dominant culture over a longer period of time will result in a drink that has the least sugar, little to no alcohol, and is highly acidic (vinegary). A batch of long-fermented kombucha will accomplish this high acidity, low sugar, and alcohol.

Welcome to the world of home-fermented brews!

Turmeric Cardamom Fizz made with ginger bug
Photo by Honami Watanabe

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