Kombucha Kombucha is a sweetened tea drink fermented by a complex colony of acetic acid bacteria, yeast and lactic acid bacteria. Rich in a diverse interplay of sweet and sour notes, natural fizz and the distinctive flavours of different teas, it is sure to delight your senses of smell and taste and give your body a wonderful treat.
For the next two months, Foodthink will publish a weekly issue of The Alchemy of Food, sharing recipes for fermented foods such as cheese and fermented chillies. Stay tuned!
1 What Is Kombucha?
Kombucha is a fermented tea beverage made from tea, sugar, water and a living microbial culture. Its taste and flavour are sometimes compared to a fizzy fruit juice. The fermentation is driven by a SCOBY (symbiotic culture of bacteria and yeast) — this colony of bacteria and yeast is also known as a “tea mother” (or mother culture).
发酵中的康普茶及康普茶成分示意图。图源：快乐Lab
发酵中的康普茶及康普茶成分示意图。图源：kombu
2 How Does Kombucha Fermentation Work?
The “tea mother” (SCOBY) of kombucha is a symbiotic community of acetic acid bacteria, yeast, lactic acid bacteria and other microorganisms. Yeast breaks down sucrose into glucose and fructose, producing carbon dioxide and ethanol in the process. The acetic acid bacteria then begin to multiply, converting glucose into gluconic acid and using the ethanol to produce acetic acid, while also generating cellulose that ultimately forms the gel-like pellicle floating on the surface of the liquid.
Structural diagram of a kombucha mother (tea fungus) under an electron microscope. Image source: A Scientific Analysis of the Tea FungusThe acetic acid then stimulates the yeast to produce even more ethanol. Lactic acid bacteria feed on the metabolic by-products of the yeast, growing and multiplying while producing lactic acid. The various organic acids generated during fermentation create a low-pH environment that, together with the tannins in the tea, helps inhibit the invasion and growth of harmful microorganisms.
3 What Is the Film on Top of Kombucha?
Mature kombucha develops an elastic film on its surface, commonly called a pellicle. Its main component is cellulose produced through the metabolism of acetic acid bacteria.
Many people assume this film is the SCOBY itself, but that is not quite right — it is actually the microbial community clinging to the pellicle that plays the key role during fermentation. Of course, you can use someone else’s pellicle as a starter, provided you make sure the microorganisms within it are still active.
The pellicle and nata de coco share similar main components. In the Philippines, people cultivate a thick pellicle on coconut water or pineapple juice mixed with sugar, then cook it into a sweet confection known as nata.
Cut the pellicle into pieces, add sugar and fruit juice, cook until the liquid is fully absorbed, then pop it in the oven — and a plate of delicious nata is ready! Image source: internet
4 Is Kombucha a Sugar-Free Drink? What Chemical Compounds Does It Contain?
The sugar in kombucha is metabolised by yeast, acetic acid bacteria and lactic acid bacteria into acids. If you ferment kombucha until it is completely sugar-free, it will likely taste like vinegar. Most people prefer their kombucha with a touch of sweetness, so some sugar inevitably remains.
Apart from sucrose, kombucha also contains a certain amount of caffeine — primarily from the tea leaves used in brewing. In 1995, kombucha enthusiast Lu Sen examined the chemical composition of kombucha and found that caffeine levels remain stable throughout fermentation, varying only with the type of tea, the quantity used and the steeping time. Like most fermented foods, kombucha does contain trace amounts of alcohol, though the level is typically below 0.5% of the total volume, which legally classifies it as a non-alcoholic beverage.
5 Where Can You Get a Mother Culture?
You can buy one online, swap with other home kombucha brewers, or cultivate your own from a bottle of raw kombucha bought in a shop.
Tomorrow, at the Fermentation Awakening Life Festival Market at Lecheng Centre in Shuangjing, Beijing, you can also taste kombucha on the spot and take home a fresh starter culture!
6 What Kind of Tea Is Best for Kombucha?
You can use black tea, green tea, white tea, oolong, dark tea or other types of tea, but steer clear of two kinds: unclean tea (poorly stored, with pesticide residue, or grown in contaminated soil) and heavily flavoured or aromatic teas such as Earl Grey, since the essential oils added to them may inhibit fermentation. You can use tea bags or loose-leaf tea, and brew as strong or as weak as you please.
Kombucha brewed with different types of tea at Happy Lab, a studio dedicated to kombucha fermentation. Image source: Happy Lab
7 Must the Tea-to-Sugar-to-Water Ratio Be Exactly 1:10:130?
Beginners are best advised to start with this ratio. But the amount of sweetener is up to personal preference — I never measure the sugar; I simply judge by taste.
8 Why Must You Use a Wide-Mouth Glass Vessel to Ferment Kombucha?
Kombucha fermentation produces acidic substances, and metal or stainless-steel vessels may corrode if exposed to acid for extended periods. Kombucha relies on aerobic fermentation — the fermentation takes place at the surface where the liquid meets oxygen — so a large vessel is best, and it should not be filled to the top, as this gives a greater surface area for fermentation. Besides a wide-mouth glass jar, you can also use a lead-free ceramic vessel.
9 Can You Replace Sucrose with Honey, Fruit Juice or Other Sweeteners?
Some people say that honey, agave, maple syrup, barley malt, fruit juice and other sweeteners work beautifully. Yet others have seen their SCOBYs shrink and die as a result. Similarly, some claim they never use tea at all — just herbal tea or fruit juice for flavouring — and still get wonderful results. I encourage you to experiment with different sweeteners and flavourings, try a few batches, and make sure your tea mother continues to thrive.
Taking home-made kombucha on a trip — a treat all of its own. Photo: Xiao Shu
10 How Long Does Kombucha Typically Take to Ferment?
The ideal temperature range for kombucha fermentation is a warm 21–30 °C. How long it takes depends on the temperature and how sour you like your drink. In warm weather, I usually ferment for 10 days, tasting every few days to decide whether to let it keep fermenting and acidifying. In colder conditions — say, at 16 °C — fermentation takes a very long time indeed. In winter, I sometimes leave my kombucha to ferment quietly for several months, until it reaches the acidity I’m after.
11 Do You Need to Sterilise Your Vessel Before Making Kombucha? If So, What Method Do You Recommend?
When making kombucha for the first time, you will need to sterilise your vessel. You can rinse it with boiling water or use a no-rinse sanitiser such as STAR SAN. Of course, since kombucha is made in a microbe-rich environment, don’t expect any sterilisation to be “absolute” — nor does kombucha-making require “absolute” sterilisation. The acidic liquid itself has antimicrobial properties that can eliminate other microbial populations.
12 Why Won’t My Kombucha Start Fermenting? What Could Be Wrong?
Perhaps your starter culture has lost its viability, or the liquid was too hot, killing the cultures you added. It may also be that the spot where you placed the starter is too cold — try moving it somewhere warmer. Chlorinated water can also inhibit fermentation.
13 How Can I Stop Mould from Growing on Kombucha? How Do I Identify Contaminants?
When you are a kombucha beginner, always remember to use mature kombucha liquid to acidify your brew — roughly 5–10% of the volume of sweet tea. This helps the kombucha’s microbial community maintain a selective environment, preventing mould from forming on the surface. You must also cover the vessel with a thin, fine-mesh cloth so that while keeping out flies and mould spores, air can still circulate.
A kombucha fermenting jar covered with cheesecloth.You can identify contaminants that harm the flavour or safety of kombucha by combining two methods: ① Smell — is there an unpleasant odour? ② Look at the pellicle — are there creases, discolouration, or visible mould growth?
If mould or contaminants appear in the jar, discard the whole batch immediately and start again, as some Aspergillus species produce water-soluble toxins.
14 Is It Normal to See Brown Sediment in Kombucha?
Brown flocculent matter is sometimes a yeast cluster, which can trap tea sediment; it may also be a pellicle in the process of forming. If it has settled to the bottom of the vessel, it could be a mixture of spent yeast and bacteria.
15 What Is Secondary Fermentation in Kombucha? How Do You Make It Fizzier?
Once your kombucha reaches the acidity you enjoy, you have several options. The simplest is to drink it and bottle the rest for the fridge. If you want to add further flavour, try fruit juice, vegetable juice, sweet herbal tea or broth, and carry out a secondary fermentation.
The secondary fermentation can be aerobic, just like the first, in an open wide-mouth vessel; alternatively, you can choose a sealed or airtight container. In an open vessel, sweet kombucha may develop a new pellicle on the surface, with growth again dominated by acetic acid bacteria. In a sealed vessel, sweet kombucha will instead produce more alcohol and lactic acid.
Transferred to narrow-necked bottles for secondary fermentation, the mother culture is now free to begin its second batch of kombucha. Photo: Xiao ShuEven if you don’t plan to add any other ingredients during the secondary fermentation, you can still achieve carbonation in the bottle. While the kombucha is still slightly sweet, pour it into sealable bottles and refrigerate. Allow the kombucha to continue fermenting in the sealed bottles for a few days to build carbonation, but remember to burp the bottles — over-carbonation can be dangerous.
16 What If My Kombucha Is Too Sour?
This means you have over-fermented — try shortening the fermentation time. However, over-soured kombucha can be used as vinegar. You can also dilute it with water or sparkling water to rescue the taste, or add a sweetener such as honey, to your personal preference.
17 How Long Can Finished Kombucha Be Stored?
In theory, indefinitely. For finished kombucha, refrigeration is generally needed to fix the flavour and keep the cultures viable.
If stored in an oxygen-rich environment, acetic acid bacteria will keep working and the taste will gradually turn sourer. If sealed and kept at room temperature with too much residual sugar, yeast will keep working and produce a little alcohol. Dormant cultures can often remain viable in kombucha for several months. That said, refrigerated and sealed storage is still the best option.
18 Does Kombucha Need to Be Kept out of Light When Brewing and Storing?
There is no need to keep it in the dark, but try to avoid direct sunlight.
19 What Is the Difference between Commercial and Homemade Kombucha?
The difference between commercial and homemade kombucha mirrors that between commercial and homemade pickles: homemade pickles aren’t necessarily tastier, and commercial pickles aren’t all made by adding vinegar or additives.
Commercial kombucha itself comes in many forms: kombucha-flavoured drinks (formulated beverages that never undergo natural fermentation), kombucha (partially naturally fermented but sterilised before bottling), and various other industrial kombucha products. Homemade kombucha, by contrast, offers far more room to play with the nuances of flavour.
20 Are There Food Safety Risks to Making Kombucha at Home?
The mycologist Stamets published an essay in 1995 titled “My Adventures on This Blob”. He compared making kombucha in an unsterilised environment to playing Russian roulette. While I greatly admire Stamets’s research into fungi, I still don’t believe home-brewing kombucha is a reckless or dangerous practice.
To insist that only kombucha made by technical experts is safe is to dismiss the homes and villages that have cultivated fermented foods for generations, and to fall into blind worship of professional expertise. Understand the conditions that create a selective environment, equip yourself with basic knowledge and awareness, and you can ferment without fear.
In March 2021, Foodthink invited Shuyu and Kiwon from Happy Lab to share their explorations in kombucha fermentation. Image source: FoodthinkWhat are you waiting for? Dive into kombucha and treat your friends to a delicious sparkling drink! Image source: Happy Lab
The Art of Fermentation Author: Sandor Katz (USA) Production: Lakeshore Culture Publisher: CITIC Publishing Group Translator: Wang Binghui Published: 20 April 2020
22 October
Come to the Fermentation Awakening Life Festival Market at Lecheng Centre, Shuangjing, Beijing
and taste Happy Lab’s kombucha!
About the Fermentation Awakening Life FestivalCivilisations of the mountains, the plains and the seas have all, independently, chosen fermentation as a means of preserving food and enriching their diets. Fermented foods draw people closer together and help us reclaim, in an age of uniform industrially produced food and ready meals, the right to individual, locally made food.
On 22 October, the Fermentation Awakening Life Festival — jointly hosted by Foodthink and the Beijing Organic Farmers Market — is set to open its doors in grand style! Beyond the fermentation market on the 22nd itself, a series of exciting events will run through to the end of December: Foodthink will publish a weekly episode of The Alchemy of Food, teaching how to make ten types of fermented foods — kombucha, cheese, fermented chillies and more — through illustrated video guides. In November, we will join forces with Lakeshore Culture to host a reading group for The Art of Fermentation, inviting fermentation enthusiasts from around the world to read along and share the joy of fermentation.
Over the next two months, our co-creation partners at the Fermentation Awakening Life Festival will also host a rich variety of fermentation-themed events at their restaurants, cafés, bookshops and other venues, exploring the magic of fermentation together. For details, keep an eye on Foodthink’s upcoming event roundup. This autumn and winter, let’s awaken life together through fermentation!
