As we’ve climbed the Homebrew Skills Tree, we’ve spent quite a bit of time learning about yeast. We’ve learned how to keep it healthy, feed it, give it oxygen at the right time, control its temperature, and measure the fermentation it creates. Kombucha gives us an opportunity to make things more interesting. This time, though, the yeast doesn’t work alone!
Kombucha is fermented sweetened tea produced by a living community of yeasts and bacteria. The yeast begins breaking down sugar and producing ethanol and carbon dioxide. Bacteria then use some of that ethanol and other metabolites to produce organic acids, especially acetic acid. Instead of trying to isolate and control one microorganism, we’re maintaining a small ecosystem in a jar. And in the middle of a North Texas summer, there’s another advantage: we can do all of this comfortably in the kitchen without boiling five gallons of wort or trying to cool a fermenter in a 100°F garage!!
So What Exactly Is Kombucha?
At its simplest, kombucha begins with tea, water, sugar, starter kombucha, and a SCOBY culture. The tea supplies flavor along with polyphenols and other compounds. Sugar supplies fermentable carbohydrates. The yeast and bacteria culture supplies the microorganisms. Like all of the fermentation we’ve talked about this year, yeast breaks sucrose into simpler sugars and metabolizes those sugars, producing ethanol and CO₂. Acetic acid bacteria then oxidize some of that ethanol into acids. Other microorganisms and metabolic pathways contribute additional organic acids, esters, and flavor compounds. The result is something quite different from the sweet tea we started with: tart, aromatic, lightly fermented and sometimes naturally sparkling.
A typical primary fermentation takes roughly 7–10 days (one of the shortest fermentation cycles we’ve encountered so far), although temperature, culture health, starting composition, and personal taste can move that considerably in either direction. That’s one of kombucha’s attractions. Compared with beer, wine, or traditional mead, we’re talking about a fermentation project that can change dramatically in a matter of days (really!).
What Is a SCOBY?
SCOBY stands for Symbiotic Culture of Bacteria and Yeast. There’s a small terminology problem, though. People commonly call the rubbery pancake floating on top of kombucha “the SCOBY.” Technically, much of the microbial culture also lives in the liquid surrounding the pancake. That cellulose mat is better described as a pellicle: a structure produced primarily by acetic acid bacteria. That distinction matters when starting a batch.
The mature SCOBY/pellicle is useful, but so is the starter liquid from a healthy previous fermentation. The acidic starter helps establish the desired microorganisms and rapidly lowers the pH of the new batch, making the environment less hospitable to unwanted organisms. So don’t think of the rubbery disk as a magical kombucha mushroom. The real SCOBY is the entire microbial community.
Why Do We Need Both Yeast and Bacteria?
This is where kombucha becomes particularly interesting for someone who already understands fermentation. The organisms essentially feed one another. Yeast gets first access to the sugar. It produces ethanol and other metabolites like we’ve seen before. Then, acetic acid bacteria can use ethanol as a substrate and convert it into acetic acid. Unlike all of our lessons to date, these bacteria aren’t an infection we’re trying to eliminate … they’re part of the recipe!
That is a significant mental shift for beer brewers, because we’ve spent years being taught that organisms such as acetic acid bacteria are things we absolutely do not want in our beer. In kombucha, we deliberately create an environment where they can thrive. The interaction among yeasts, acetic acid bacteria, and, in some cultures, lactic acid bacteria produces the organic acids and other metabolites that give kombucha its characteristic flavor.
Does the Tea Matter?
Absolutely. Traditional kombucha is commonly made from black tea, green tea, or combinations of teas from Camellia sinensis. These provide not only flavor but also compounds that support the fermentation and contribute polyphenols and antioxidants to the finished beverage. Different teas create genuinely different kombuchas. Black tea tends to produce a fuller, more robust character. Green tea can be lighter, fresher and more delicate. Oolong occupies interesting territory between them. Blending teas gives the brewer another design variable.
This is where kombucha begins looking familiar to a beer, wine or mead maker. Choosing the tea is no different conceptually from choosing malt, grapes, honey, or apples. The fermentation organisms may transform the ingredients, but the raw material still matters. Once you’re comfortable with the process, exploring different teas becomes one of the artistic parts of kombucha making.
Does Kombucha Need Yeast Nutrient?
Usually, traditional tea-based kombucha does not require the nutrient schedules we’ve discussed for mead. Remember why we add Fermaid O, Fermaid K, DAP, and other nutrients to honey fermentations: honey contains lots of sugar but very little yeast-assimilable nitrogen.
Kombucha is a different microbial system with different requirements. A healthy, established culture fermenting properly prepared sweetened tea generally doesn’t need the brewer to begin adding conventional beer or mead yeast nutrients. More isn’t always better. If the culture is healthy and fermentation is proceeding normally, don’t add nutrients simply because they’re sitting on the homebrew shelf.
How Do I Know When It’s Done?
This may be my favorite part of kombucha making: You decide!
There isn’t one universally correct finishing gravity. Early in fermentation, the kombucha remains relatively sweet. As fermentation proceeds, sweetness decreases and acidity increases. Eventually it reaches the balance that tastes right to you. Taste is therefore an important instrument. But by this point on the Homebrew Skills Tree, we know better than to rely exclusively on our tongue when we have useful measurements available. True story .. we were making kombucha one week. For several days, it was too sweet. We had a guest over the weekend, and didn’t pay attention to it from Friday afternoon till Sunday afternoon. Sure enough, in just those couple of days it went from just a bit too sweet to a bit too tart (for may palate, anyway 😉 ). We still drank it of course, but like any recipe and fermentation, it needs to be kept an eye on, especially when the environment changes so quickly.
A pH meter or good pH test strips lets you follow acidification from batch to batch. Measuring pH doesn’t tell you exactly how sweet the kombucha is, just as we learned in our wine titration article that pH doesn’t tell us total acidity. But it gives us an objective measurement of how the fermentation is developing and helps us reproduce a successful process. If sweetness matters, gravity or Brix measurements can also provide information, although kombucha is more complicated than beer because alcohol and organic acids change density and refractive index as fermentation proceeds. A hydrometer or refractometer reading shouldn’t be interpreted as simply “this much sugar remains.”
The most practical combination is therefore taste + pH + time, with good batch notes. Maybe you discover that your favorite kombucha from a particular tea consistently tastes right after eight days at your kitchen temperature and around a particular pH. Now you’re not guessing anymore. You’re developing a process.
What Does Temperature Do?
Like every fermentation we’ve studied, kombucha responds to temperature. A warmer kitchen generally means faster microbial metabolism and faster acid development. A cooler room slows things down.
That makes kombucha particularly convenient during summer. A normal indoor room temperature is generally quite comfortable for an active culture, even while the garage outside is approaching triple digits. But hotter isn’t automatically better either. Very high temperatures can change the balance of organisms and flavors, just as they do in beer, wine and mead. Keep the culture in a reasonably stable indoor environment, out of direct sunlight, and let the microorganisms establish their own rhythm.
Is Sanitation Still Important If We’re Intentionally Growing Bacteria?
Very much so. We’re not trying to eliminate all microorganisms. We’re trying to give the right community an overwhelming advantage.
That’s exactly why sanitation matters. Use a clean fermentation vessel, clean utensils and properly cleaned equipment. Keep the vessel covered with a breathable cloth or tightly woven cover secured against fruit flies and debris. Unlike beer fermentation, however, kombucha’s acetic acid bacteria require oxygen .. it respirates! We don’t normally seal primary fermentation under an airlock. The acidic environment provides additional protection, but acidity isn’t permission to work dirty.
One particularly important warning sign is fuzzy mold. A new cream-colored or translucent pellicle is normal. Brown yeast strands are normal. Strange-looking layers can be normal. Dry, fuzzy growth in blue, green, black or white is not normal. If genuine mold develops, don’t try to scoop it off and rescue the batch. Discard the batch and culture and start again with a healthy one.
How Do I Take Care of My SCOBY Between Batches?
A healthy culture is surprisingly resilient. If you’re making another batch soon, retain some mature kombucha as starter liquid along with the pellicle and introduce them to the next batch of cooled sweet tea. If you want to take a break, you can maintain what kombucha makers affectionately call a SCOBY hotel. This is simply a clean container holding mature starter liquid and one or more pellicles. Rather than making finished kombucha for drinking, you’re maintaining a reservoir of healthy culture. Keep enough liquid around the culture to prevent it from drying out. If stored for an extended period, periodically replenish it with fresh sweet tea. The liquid in a mature SCOBY hotel can become extremely acidic. That’s not necessarily a problem. In fact, strong mature liquid can make excellent starter for a new batch.
What If My SCOBY Gets Huge?
It probably will. The cellulose pellicle can continue adding layers with each fermentation until you have something resembling a stack of pancakes. You don’t need all of it.
Peel off older layers, discard or compost them, share healthy cultures with another kombucha maker, or move extras into the SCOBY hotel. Remember that the thickness of the pellicle isn’t a measure of fermentation strength. A huge rubbery SCOBY isn’t necessarily better than a modest one accompanied by plenty of healthy starter liquid. The microorganisms in the liquid are doing plenty of the work.
Can I Flavor Kombucha Like Mead?
Absolutely, and this is where kombucha becomes an extraordinary playground for experimentation. After primary fermentation reaches the acidity and sweetness you like, you can introduce fruit puree, fruit juice, herbs, spices, ginger, citrus peel, or other flavor ingredients. Consider raspberry, peach, mango, blueberry, ginger-lemon, hibiscus, mint, or combinations of several ingredients. Much like meadmaking, the base fermentation becomes a canvas. But fruit introduces something else we’ve encountered many times on the Skills Tree: more sugar. And living yeast sees new sugar as dinner.
Will Fruit Start Fermentation Again?
Yes, very likely. Adding fruit or juice introduces fermentable sugars into a beverage that still contains active yeast. Fermentation can resume. In an open or breathable vessel, much of the CO₂ simply escapes. In a sealed pressure-rated bottle, that CO₂ becomes carbonation. That’s how many kombucha makers create naturally sparkling kombucha during a secondary fermentation. It is also why you need to respect the process.
Warm kombucha containing active culture, additional fruit sugar, and a sealed bottle is essentially a small bottle-conditioning fermentation. Pressure can continue increasing. Use appropriate bottles, monitor the process, and refrigerate when you’ve reached the carbonation level you want. Refrigeration dramatically slows microbial activity, but it doesn’t sterilize the beverage. This is another place where the brewing skills we’ve already learned transfer directly to kombucha.
Should I Use Potassium Sorbate?
Generally, no. Potassium sorbate is useful in certain wine, cider, and mead processes when we want to inhibit yeast reproduction before backsweetening. That’s not usually how traditional live kombucha is managed. Kombucha depends upon an active microbial culture. Stabilizing it chemically works against one of the defining characteristics of the beverage. Instead, kombucha makers generally manage fermentation through time, temperature, refrigeration and sugar availability. If you’re adding fruit for flavor and carbonation, you actually want some continued fermentation. Once the flavor and carbonation are where you want them, refrigeration becomes your primary control.
How Long Will Homemade Kombucha Keep?
Properly refrigerated kombucha can remain usable for quite some time, but it isn’t frozen in time. The organisms remain alive. Fermentation slows dramatically in the refrigerator but can continue gradually. Flavor can become more acidic, sweetness can decline, and carbonation can continue developing. For homebrewers, think in terms of weeks rather than trying to assign a precise expiration date. Make manageable batches, keep them refrigerated, inspect and taste them, and enjoy them while their flavor is at its best. And remember that homemade kombucha can contain some alcohol. Fermentation creates ethanol before bacteria metabolize it, and the amount can vary depending on culture, sugar, temperature, time and secondary fermentation.
And Is Kombucha Really Good for You?
This is where we need to separate an interesting biological hypothesis from something science has actually demonstrated in humans. Kombucha contains tea-derived polyphenols, organic acids, and a diverse microbial community, and fermentation produces additional bioactive compounds. Researchers have found antioxidant and antimicrobial properties in laboratory studies, and there are plausible reasons that fermented foods may influence the intestinal microbiome. Recent human studies are beginning to investigate that question directly. Some have detected changes in the abundance of particular gut microorganisms after kombucha consumption. But the clinical evidence remains limited, studies are relatively small, and researchers have not established that drinking ordinary kombucha reliably produces broad improvements in digestion, immunity, inflammation, weight loss, or general health.
That’s an important distinction. Kombucha is a fascinating fermented beverage containing microorganisms and fermentation products that may interact with our gut ecosystem. That’s scientifically interesting. Calling it a treatment or cure for health conditions goes well beyond the evidence we currently have. So enjoy kombucha because it’s refreshing, complex, customizable, and fun to ferment. If ongoing research eventually establishes additional health benefits, that’s a bonus.
A Fermentation Laboratory on Your Kitchen Counter
Kombucha might look very different from beer, but by now you should recognize almost everything that’s happening. We have yeast consuming sugar. We have temperature affecting metabolism. We have bacteria producing acids. We have pH changing. We have oxygen requirements. We have sanitation concerns. We can measure the fermentation, manipulate ingredients, and decide when the balance tastes right. Then we can introduce fruit, start another fermentation, and manage carbonation.
The microorganisms are different, but the fermentation skills aren’t. And that’s exactly why kombucha belongs on the Homebrew Skills Tree!
Where Are You on the Homebrew Skills Tree?
Your branches are spreading into another fermentation discipline. You’ve learned that a SCOBY is really a community of bacteria and yeast, that those organisms cooperate to transform sweet tea into an acidic fermented beverage, and that temperature, oxygen, sanitation, sugar, and pH all influence that ecosystem. You’ve also learned to manage a culture between batches, recognize when something doesn’t look right, introduce new flavors, and understand why adding fruit can restart fermentation and create carbonation. Most importantly, you’re seeing something that becomes clearer the farther we climb this tree:
Beer brewing, winemaking, meadmaking, cider making, and kombucha aren’t isolated hobbies. They’re different applications of the same fermentation science. Once you understand the science, learning a new branch becomes much, MUCH easier!
Here is a link to all of our kombucha tea, SCOBYs, bottles, and fermenters at NTHBS. Stop by the store, reply here, or email us if you have any questions about your finings and options.
Cheers!
-eric-