Kombucha is a naturally fermented tea that has been enjoyed in various forms for generations and has become increasingly popular as an alternative to soft drinks and other sweetened beverages.
At its simplest, kombucha is made from tea, water, sugar and a living culture of yeasts and bacteria. During fermentation, these microorganisms transform the sweetened tea, producing organic acids, carbon dioxide, small amounts of alcohol and a wide range of other compounds that give kombucha its distinctive refreshing, slightly sweet and tangy flavour.
One of the attractions of kombucha is that it can be made at home with relatively simple equipment. Once you have a healthy SCOBY and starter culture, the culture can be maintained and used to produce batch after batch of kombucha.
In this guide, we’ll explain what kombucha is, how a SCOBY works, what happens during fermentation, what the current research says about potential health benefits, and what you need to know before making your own.
Table Of Contents
- What Is Kombucha?
- What Are SCOBY ?
- What Is Kombucha Made From?
- How Does Kombucha Fermentation Work?
- What Does Kombucha Taste Like?
- Is Kombucha Healthy?
- Is All Kombucha the Same?
- Does Kombucha Still Contain Sugar?
- Does Kombucha Contain Alcohol?
- Does Kombucha Contain Caffeine?
- Is Homemade Kombucha Safe?
- Can You Flavour Kombucha?
- How Long Does Kombucha Take to Ferment?
- Can You Reuse a Kombucha SCOBY?
- How Do You Make Kombucha at Home?
- Start Making Your Own Kombucha
What Is Kombucha?
Kombucha begins as sweetened tea.
Traditionally, black tea is commonly used, although green tea and combinations of different teas can also be used.
A SCOBY and starter culture are added to the prepared sweet tea. The microorganisms in the culture then begin fermenting some of the sugar.
Over time, the tea becomes less sweet and more acidic. The result is the drink we know as kombucha.
Depending on how it is made, kombucha can range from relatively sweet and mild to noticeably tart and acidic. It may also have natural carbonation or be given additional flavour and carbonation through a second fermentation.
What are SCOBY?
SCOBY stands for:
Symbiotic Culture of Bacteria and Yeast
The name describes the community of microorganisms responsible for kombucha fermentation.
The familiar rubbery or gelatinous disc that forms on top of kombucha is commonly referred to as the SCOBY. More precisely, this layer is a cellulose-rich pellicle produced by the culture.
The Starter Liquid Is Just as Important
An important point for new kombucha brewers is that the solid SCOBY is only part of the story.
The starter liquid contains an active population of microorganisms and, importantly, enough acidity to help establish suitable conditions for a new batch.
For that reason, a good kombucha starter kit should provide both a healthy culture and sufficient active starter liquid.
The combination gives the new fermentation a much better start than simply putting a piece of SCOBY into sweet tea.
What Is Kombucha Made From?
Although finished kombucha can contain many different compounds, the basic ingredients are surprisingly simple.
Tea
Tea supplies flavour as well as naturally occurring compounds such as polyphenols.
Green tea can also be used, either by itself or blended with black tea.
Black tea is an excellent traditional base for kombucha and produces a robust fermentation and characteristic flavour.
Once you become more experienced, different teas and flavouring ingredients can be used to create very different styles of kombucha.
Sugar
Sugar is essential to the fermentation process.
It isn’t simply added to make the drink sweet. The yeasts and bacteria use sugar as part of their metabolism during fermentation.
Some of the original sugar is consumed, but fermentation does not necessarily remove all of it. The amount remaining in finished kombucha depends on the recipe, fermentation time, temperature and activity of the culture.
This is why it is incorrect to assume that every kombucha is automatically sugar-free.
Water
Because water makes up most of the finished drink, water quality matters.
Water should be suitable for drinking and should not contain levels of sanitising chemicals or other substances that adversely affect the culture.
SCOBY and Starter Culture
The final essential ingredient is your active kombucha culture.
The yeasts and bacteria work together, creating the fermentation that changes ordinary sweetened tea into kombucha.
[LINK: HOMEBREW WORKS SCOBY STARTER KIT]
How Does Kombucha Fermentation Work?
Kombucha fermentation is more complicated than simply “good bacteria eating sugar”.
It is actually a cooperative fermentation involving different microorganisms.
The Yeasts Begin Breaking Down the Sugar
The yeasts in the culture help break down sugars and produce compounds including ethanol and carbon dioxide.
This is one reason kombucha can naturally contain a small amount of alcohol.
Bacteria Produce Organic Acids
Acetic-acid bacteria within the culture use some of the fermentation products produced by the yeasts and form organic acids, including acetic acid.
These acids contribute to kombucha’s characteristic tart flavour and decreasing pH.
As fermentation progresses, the balance between sweetness and acidity changes.
Why Kombucha Changes From Sweet to Tart
Freshly prepared kombucha tea contains a considerable amount of sugar because the culture needs food to begin fermentation.
Early in fermentation, the liquid can still taste very sweet.
As fermentation continues, the flavour gradually develops:
Sweet tea → mildly tart → balanced sweet/tart kombucha → increasingly acidic kombucha
This is one reason fermentation time has such a significant influence on the finished drink.
Temperature also has an important effect. A warm, active fermentation will generally progress more quickly than one kept under cooler conditions.
What Does Kombucha Taste Like?
Good kombucha should have a pleasant balance of sweetness, acidity and tea character.
It is difficult to describe one universal kombucha flavour because it can vary enormously.
A traditional black-tea kombucha might be slightly sweet, fruity and acidic with a subtle vinegar-like sharpness.
The finished kombucha can then be flavoured with ingredients such as:
- Ginger
- Berries
- Passionfruit
- Citrus
- Beetroot
- Herbs
- Spices
- Other fruits
This gives home brewers enormous scope to experiment.
For example, ginger can add warmth and freshness, blackcurrant can provide colour and berry character, while beetroot can produce an earthy flavour and striking colour.
We’ll cover flavouring and second fermentation in a separate HomeBrew Works guide.
Is Kombucha Healthy?
This is where it is worth separating what we know about kombucha from some of the claims made about it.
Kombucha contains a complex mixture of tea-derived compounds, microorganisms and substances created during fermentation. Research into its potential health effects is growing, but human clinical research is still relatively limited.
It is therefore better to think of kombucha as an interesting fermented tea beverage, rather than as a medicine or treatment.
Tea Polyphenols and Antioxidant Compounds
Tea naturally contains plant compounds known as polyphenols.
These compounds remain present to varying degrees after fermentation, while fermentation can also change the chemical composition of the original tea.
Laboratory studies have demonstrated antioxidant activity in kombucha and its constituents. However, demonstrating antioxidant activity in a laboratory is not the same as proving that drinking kombucha produces a particular health outcome in people.
This is an important distinction when considering some of the stronger health claims sometimes made about kombucha.
Live Cultures and the Gut Microbiome
Traditionally produced, unpasteurised kombucha may contain living microorganisms originating from its fermentation culture.
This has created considerable interest in kombucha and the gut microbiome.
Some recent human studies have found changes in certain gut microbial populations following kombucha consumption. However, the studies conducted so far have generally involved relatively small groups of people, and the results don’t yet establish that all kombucha produces a particular digestive or health benefit.
It is also worth noting that the microbial composition of one kombucha can be quite different from another.
For this reason, describing kombucha simply as a “probiotic” can be misleading. A scientifically demonstrated probiotic effect normally relates to particular microorganisms, in appropriate amounts, that have been shown to provide a health benefit.
Kombucha is more accurately described generally as a fermented drink that may contain live cultures.
Kombucha and Blood Sugar Research
There has also been some interesting early research into kombucha and blood glucose.
One small pilot study involving people with type 2 diabetes reported a reduction in fasting blood glucose after four weeks of kombucha consumption compared with baseline. However, the study involved only 12 participants, so considerably larger studies are needed before firm conclusions can be drawn.
Other recent clinical studies have examined metabolic markers and have produced mixed or modest results.
This is a promising area of research, but kombucha should not be considered a treatment for diabetes or a substitute for medical treatment or dietary advice.
Organic Acids
Kombucha fermentation produces a variety of organic acids, with acetic acid being one of the most recognisable.
These acids are an important part of kombucha’s flavour and chemistry and contribute to its characteristic low pH.
You’ll sometimes see very strong claims online about these compounds “detoxifying” the body. At present, there isn’t sufficient human clinical evidence to justify treating kombucha as a detoxification therapy.
What Has Kombucha Not Been Proven to Do?
You can find some extraordinary claims about kombucha online.
It has at various times been claimed to cure or prevent serious diseases, detoxify the liver, produce dramatic weight loss, boost immunity and treat numerous medical conditions.
Evidence supporting claims of this magnitude is lacking.
There is good reason to continue researching kombucha because its fermentation chemistry is fascinating and early studies are producing interesting results. But there is an equally good reason not to exaggerate what the science currently demonstrates.
For us, that is part of taking kombucha seriously.
Is All Kombucha the Same?
No.
This is particularly important when discussing kombucha’s composition or possible health properties.
The finished beverage can vary according to:
- Tea variety
- Amount of sugar
- SCOBY microorganisms
- Amount of starter culture
- Fermentation temperature
- Fermentation time
- Oxygen exposure
- Added fruits and other ingredients
- Secondary fermentation
- Filtration
- Pasteurisation
- Refrigeration and storage conditions
Two products sold as kombucha can therefore have quite different levels of sugar, acidity, alcohol and viable microorganisms.
This is also why controlled brewing becomes increasingly important when kombucha is produced commercially.
Does Kombucha Still Contain Sugar?
Usually, yes.
Although microorganisms consume some sugar during fermentation, some normally remains in the finished beverage.
How much remains cannot reliably be determined simply by how long the kombucha has fermented or how sour it tastes.
For home brewing, taste can help you decide when you enjoy the balance of sweetness and acidity.
For commercial production, sugar levels should be properly measured and controlled if nutritional information or sugar-related claims are being made.
Does Kombucha Contain Alcohol?
Kombucha fermentation naturally produces some ethanol because yeast converts sugars during fermentation.
The amount can vary considerably depending on the culture and brewing conditions.
Factors that can affect alcohol production include:
- Sugar concentration
- Yeast population
- Temperature
- Fermentation time
- Availability of oxygen
- Sealed secondary fermentation
- Added fruit or sugar
- Storage conditions
This is particularly important for commercial kombucha because fermentation can continue after the primary brewing stage if active microorganisms and fermentable sugars remain.
Home-brewed kombucha should therefore not automatically be assumed to contain zero alcohol.
We will cover alcohol formation, measurement and control in kombucha in a separate guide.
Does Kombucha Contain Caffeine?
Kombucha made with traditional tea generally contains some caffeine because caffeine is naturally present in the tea used to make it.
The amount will depend on factors such as the type of tea, quantity used and brewing method.
Fermentation does not provide a reliable way of guaranteeing that all caffeine has been removed.
Anyone specifically avoiding caffeine should therefore check how a particular kombucha has been produced rather than assuming fermented tea is caffeine-free.
Is Homemade Kombucha Safe?
Kombucha has been made successfully at home for many years, but good brewing practice is important.
Unlike wort during beer brewing, kombucha isn’t normally subjected to a sterilising boil after fermentation. You are deliberately encouraging a particular community of microorganisms to grow.
Clean equipment, a healthy starter culture and appropriate acidity therefore matter.
Cleanliness Is Essential
Always begin with thoroughly clean equipment and clean hands.
Avoid allowing dirty utensils, food residue or other contaminants to contact your kombucha.
Use a Healthy Starter Culture
Starting with a strong culture and sufficient acidic starter liquid helps establish the environment required for normal kombucha fermentation.
Know the Difference Between a Normal SCOBY and Mould
A new kombucha brewer can sometimes be alarmed by the appearance of a SCOBY.
A developing pellicle can look uneven, translucent, brown, lumpy or quite strange. Brown yeast strands and sediment can also be completely normal.
Dry, fuzzy mould growth is not normal.
If genuine mould develops, the batch should be discarded rather than attempting to remove the mould and continue fermentation.
We will provide a separate Kombucha Troubleshooting Guide showing what normal SCOBY development looks like and what warning signs to watch for.
Can You Flavour Kombucha?
Absolutely.
Flavouring is one of the most enjoyable parts of making your own kombucha.
After the initial fermentation, kombucha can be flavoured using fruits, juices, herbs, spices and other ingredients.
Popular combinations include:
Ginger & Lemon
Fresh, sharp and refreshing.
Blackcurrant & Ginger
Deep berry character with the bite of ginger.
Beetroot & Ginger
Earthy, colourful and distinctive.
Passionfruit
Aromatic, tropical and naturally suited to kombucha’s acidity.
Mixed Berry
A simple way to produce a fruity, approachable kombucha.
Flavour additions containing sugar can restart vigorous fermentation, particularly when kombucha is sealed in a bottle. This can produce natural carbonation but also increases pressure inside the container.
For that reason, secondary fermentation should be carried out using containers designed to safely withstand pressure.
We’ll explain the complete process in our upcoming guide to flavouring and naturally carbonating kombucha.
How Long Does Kombucha Take to Ferment?
There isn’t one exact fermentation time that works in every situation.
Temperature, culture strength, batch size, sugar concentration and personal taste all have an effect.
The important principle is to observe how your kombucha develops rather than treating a particular number of days as an absolute rule.
As the culture becomes established, you will normally notice increasing acidity and decreasing sweetness.
When you’re learning, keeping a simple brewing record is useful. Record the date, recipe, room temperature and how the kombucha tastes at different stages.
You’ll quickly begin to understand how your culture behaves in your particular brewing environment.
Can You Reuse a Kombucha SCOBY?
Yes.
One of the advantages of brewing kombucha is that a healthy culture can be maintained from one batch to the next.
During fermentation, a new pellicle often develops across the surface. Over repeated batches, layers can accumulate.
You don’t need an enormous stack of SCOBY layers to make kombucha successfully.
More important is maintaining healthy active culture and sufficient starter liquid for your next batch.
Some kombucha should therefore always be reserved as starter culture rather than drinking or flavouring the entire batch.
How Do You Make Kombucha at Home?
The basic process is straightforward:
- Brew the tea.
- Dissolve the required sugar.
- Allow the sweet tea to cool.
- Add the SCOBY and active starter liquid.
- Cover the fermentation vessel appropriately.
- Allow the kombucha to ferment.
- Taste and monitor its development.
- Reserve starter liquid for your next batch.
- Drink the kombucha as it is, or flavour and carbonate it in a second fermentation.
Although the basic process is simple, quantities, temperatures and good handling practices matter.
For that reason, we’ve created a separate step-by-step guide specifically for people using our starter culture:
[LINK: HOW TO MAKE KOMBUCHA WITH A HOMEBREW WORKS SCOBY STARTER KIT](Work In Progress)
Start Making Your Own Kombucha
Making your own kombucha gives you control over the tea, fermentation time, sweetness and flavours you use.
Once you’ve established a healthy culture, you can experiment with everything from traditional black-tea kombucha through to ginger, berries, passionfruit, beetroot and your own flavour combinations.
The HomeBrew Works Kombucha SCOBY Starter Kit provides the culture and starter needed to begin your first batch.
[LINK: SHOP HOMEBREW WORKS KOMBUCHA SCOBY STARTER KIT]
For your first brew, follow our full step-by-step instructions:
[LINK: HOW TO MAKE KOMBUCHA USING OUR SCOBY STARTER KIT](Work In Progress)
From there, we’ll help you explore flavouring, carbonation, SCOBY care, troubleshooting and more advanced kombucha brewing.