Have you ever tried to make your own kombucha from scratch? It is surprisingly simple, very interesting, and incredibly tasty. Kombucha is made by feeding a symbiotic culture of bacteria and yeast (SCOBY) with sweetened tea. The yeast and bacteria help each other convert the tea to a really tasty, fizzy, sour drink. (It is basically carbonated vinegar but that might not sound too appetizing). For this post, I ended up writing more or less all I know about kombucha making so the post became quite long. Feel free to jump to the section(s) that interest you the most.

• Biology – what is going on?
• Make your own SCOBY from scratch
• Making kombucha
• Equipment I use
• Common questions

Kombucha has a long history and likely comes from Manchuria (modern day North Eastern China) where it was drank at least as early as 220 B.C.E. for its detoxifying and energizing abilities ​[1]​. The drink was brought to Japan in the 5th century C.E., potentially by a Korean physician named Kombu, which might be the origin of the name kombucha (“Kombu’s tea”). Another version of the English name can be that it is a misinterpretation where tea from seaweed (Japanese: kombu) was mistaken as the name for fermented teas in general ​[2]​.

Regardless of the origin of the name, kombucha slowly spread across Russia, through Eastern Europe and reached Germany around the end of the 19th century ​[1]​. Around the 1950s and onward, the drink spread further into Europe. But what is kombucha and what is going on in that floating, fungus-like thing?

Biology

Kombucha is a fermented tea. Over several days, microbes living in a jar of sweetened tea convert the sugar into a range of tasty molecules, predominantly acetic acid (vinegar) ​[3]​. Kombucha is fermented by two types of microbes: yeast and bacteria. Together, these form a Symbiotic Culture of Bacteria and Yeast (SCOBY). This is that floaty, spongy mushroom-looking thing floating on top of the sweet tea, sometimes called a mother, kombucha mother or a pellicle. The yeast cells consume sugar and create ethanol (normal alcohol) which the bacteria then eat, producing a range of acids and other molecules.

A floating cellulose colony

The most striking feature of kombucha brewing, the SCOBY, is produced by the bacteria. In addition to making acids they produce cellulose ​[3]​. Cellulose is a long molecule which is basically a long chain of connected sugar molecules, similar to starch or glycogen which plants (starch) and animals (glycogen) use to store energy. Cellulose is not used to store energy but rather acts as a structural element – it is one of the molecules plants use to create their bodies. When the bacteria in the SCOBY produce cellulose, the strands entangle and stick to each other, creating a giant, floating mesh where most of the bacteria and yeast cells live. This is good news since the bacteria require oxygen to do their magic.

The perfect environment

In a previous post about fermentation, I wrote about how important it is to create an environment which only your specific microorganisms survive in, so you get the right kind of growth for the project. For instance, we saw that adding salt and excluding oxygen removed almost all bacteria but lactic acid bacteria (LAB) for your basic LAB ferment. The LAB then go on to replicate and produce a lot of lactic acid as they munch away on your vegetables, reducing the pH and killing any remaining bacteria, spores and toxins (e.g. from the dreaded botulism causing clostridium botulinum) ​[4]​.

The bacteria (>85 % glucanobacteria, with some Lactobacillus and Acetobacter ​[5]​)  in the SCOBY and kombucha produce a lot of different of organic acids ​[3]​. Mainly acetic acid (vinegar) but also tartaric acid, malic acid and some citric acid. These acids do the same job as the lactic acid in LAB fermentation: they create a very acidic environment only a few microorganisms can survive in. Luckily, the yeast types (>95% Zygosaccharomyces ​[5]​) in kombucha can survive these environments as well, gaining protection from the work the bacteria do.

Back slopping and inoculation

To help the microorganisms in the kombucha protect themselves before they have a chance to produce their own acids, kombucha brewing starts with lowering the pH of the kombucha (make it more acidic). This is typically done by saving some old kombucha and pouring it into the new batch, creating a friendly environment for your friends living in the SCOBY. In fermentation terms, this is called back slopping, where part of an old batch is used to create the new batch.

Adding old kombucha as well as an old SCOBY also introduces the correct microorganisms from the start, a fermentation trick called inoculation. For instance, often when you do LAB ferments or when you start a brand new sourdough, you just rely on yeast and bacteria present on your ingredients and in the air to spontaneously join your growing culture. For a more controlled process, you can add your own, well defined microorganisms, such as when baking with yeast or brewing wine/beer where you add well defined stains artificially. You use the same inoculation concept when you feed your sourdough and you can do the same for your LAB ferment: if you have a particularly good batch of sauerkraut, you can keep some and add to your next batch, allowing the same little LAB helpers to continue doing their thing. For kombucha brewing, inoculation takes the form of adding old kombucha and the SCOBY, both of which contain the correct microorganisms.

Health claims

There are many claims about the health benefits of kombucha but there doesn’t seem to be any human data on the topic ​[3]​. This doesn’t mean that kombucha is not healthy, just that it hasn’t been studied. Simple experiments in test tubes show that kombucha contains anti-oxidants which is not too surprising (as tea does too) ​[3]​. Some cell culture experiments have shown to kill or inhibit growth of specific cancer cells but studies on cells in Petri dishes ​[1]​ do not always translate to results in humans and animals (for one, the environment the cells experience in a hard, plastic dish is far removed from their complex 3D environment in the body). Studies in rats have also shown it to be have beneficial effects in diabetic patients ​[3]​. Jayabalan et al. included a table of animal experiments from the scientific literature in their kombucha review paper which is a good start if you want to learn more about scientifically, substantiated health claims (in animals, not humans) ​[1]​.

How to make kombucha

You need a SCOBY

To make your own kombucha you absolutely need your own symbiotic culture of bacteria and yeast, SCOBY. But fear not, it is very simple. One way is to just buy a small SCOBY with starter kombucha online but that is not very exciting. Another popular method is to ask around and see if anyone around you is making kombucha (great for making friends and sharing interests) or you can check online forums, such as this subreddit: r/findascoby for giveaways in your area.

Or if you just want that little extra bit of from-scratch feeling, you can make your own SCOBY from a bottle of store-bought kombucha. Sound daunting? It is just slightly more difficult than brewing a cup of tea. Short version: brew tea with lots of sugar, wait for it to cool, pour in unpasteurized kombucha, wait for 10-14 days. Done. Keep the growing SCOBY in a jar with access to air (e.g. wide mouth mason jar covered with a coffee filter). The SCOBY will start forming after 24-48 h and then you can watch it grow until it is thick enough to handle (10-14 days).

How to make your own SCOBY

Instructions can also be found here as a separate recipe post.

1. Bring 125 mL water with 2 tbsp sugar to a simmer. Wait for the sugar to dissolve.
2. Turn of the heat and add a teabag. Let sit for 10 min.
3. Discard teabag and pour tea into a 1 L jar (wide mouth mason jars are great).
4. Add 125 mL room temp water to help bring down the temperature.
5. When the tea is at room temperature, pour in a small bottle (~473 mL / 16 oz) of unpasteurized kombucha. Be sure to get the sediment as well, if any.
6. Cover the jar with something that allows air exchange, such as a coffee filter, tea towel, cheesecloth… Secure with a rubber band.
7. Put away in dark place and leave it be for ~10-14 days. A SCOBY will start forming after 24-48 h and you can look daily to see it grow.

Brewing kombucha

Once you have a SCOBY in your home (be it from a store, a friend (old or brand new) or one you created on your own), you are ready to make kombucha. This is a two step process where you first feed the SCOBY sweet tea and let it do its magic. After a week or so, the sweet tea will have lost most of its sweetness and developed a lot of flavour and acetic acid. (As described above, the yeast feeds on the sugar and turn it into alcohol which the bacteria consume and turn into acetic acid, or vinegar.) This brew is kombucha and is ready to drink but many people prefer a 2nd fermentation step to add other flavours and carbonate the kombucha.

In the second fermentation step, you pour the basic kombucha into a bottle, add some sugar and some flavour component, such as mint leaves or grated ginger, and let it sit for another few days. The large, floating colony (i.e. the SCOBY) is left behind but some yeast and bacteria will remain in the basic kombucha and colonize the bottle. They will feed on the sugar and create carbon dioxide (CO₂) which will dissolve in the kombucha, carbonating it.

Flavour ideas

When making kombucha, you can drink it plain, straight out of the jar the SCOBY lives in. But many people prefer a 2nd fermentation where the kombucha gets carbonated and you have the opportunity to add other flavour components, as detailed in the recipe below. To find flavours you can try whatever you can think of or you can read commercial kombucha labels for ideas or check out different blogs online. I have come to enjoy these quite simple flavours:

• Ginger, grated, 1 tbsp per litre kombucha
• Mint leaves, torn, 1-2 tbsp per litre kombucha. I often buy a bunch and freeze what I don’t use. The frozen leaves can go straight in.
• Berries, fresh or frozen, 2 tbsp per litre kombucha. Mash them a little bit to allow juice to come out.

Word of warning about pressure

The generation of carbon dioxide will create a pressure in the bottle (which is how the kombucha gets carbonated). Use bottles that can withstand a pressure. There are bottles that are just for decoration, don’t use those as they can shatter under pressure. I use old kombucha bottles from the store since they are made for this purpose. Also, be careful when you open the bottle. If you’re lucky and the carbonation has developed well, the kombucha will start to fizz and foam and will try to spill over. If you’re unlucky, you might have developed way too much pressure and the cap can shoot off. This happened to our room mate when she was making tepache (a Mexican fermented pineapple/habanero drink which you should definitely try if you haven’t). But be careful. Don’t have your face above the bottle when opening. If you use a very sweet flavour additive, such as pureed fruit, more pressure will develop. In that case, ferment for a shorter period of time and omit the added sugar.

Equipment

For taking care of your SCOBY and brewing your kombucha, you can pretty much use whatever you want. But bear in mind that kombucha is quite acidic so don’t use metal for long term storage, as acids destroy metals over time. If you’re new to brewing kombucha, you can use my list of equipment as a starting point while figuring out what works for you.

• 4 L decorative mason jar. Just a big jar from a home decoration store. Does not need to withstand pressure and does not need a lid, will be covered by cloth or similar
• Cheesecloth and rubber band. Cover the large jar with thin cloth to allow air exchange and prevent stuff from falling in. Rubber band to secure cloth.
• Large pot: For making the tea, 2+ L.
• Glass bowl: For resting your SCOBY on while you work. Can be just a plate as well.
• Scale: I like to weigh out the sugar but you can just measure volume.
• Old kombucha bottles: For 2nd fermentation, can withstand pressure. Maybe the caps degrade over time so you might want to replace after a while but I haven’t experienced any adverse effects. Your bottles need to withstand pressure. Many bottles are not designed for this. See warning above.
• Small sieve: When serving the kombucha, I like to pour it through a small sieve to catch any flavour enhancers, like grated ginger, or any baby SCOBY that might have formed.

How to take care of your SCOBY

The SCOBY is a living colony of bacteria and yeast and needs to be fed regularly, just like a sourdough. When you make your flavoured kombucha, it is simple and common practice to make new sweet tea for the SCOBY, as in the recipe below. But if you at some point feel you are struggling to keep up with drinking all that kombucha and your friends have started to decline all those bottles you keep giving away, you might want to take a break form brewing kombucha.

Taking a break from kombucha brewing

If you at some point feel that you want to take a break from making and drinking kombucha, you don’t have to worry much. You won’t have to discard your SCOBY and start over. They are very forgiving colonies and can be left in their sweet tea for 4-6 weeks, maybe longer. The only thing is that the sweet tea will turn more and more sour as the sugar is being converted into acetic acid (vinegar). When you are ready to start making kombucha for yourself again, you might want to do a feeding round first and not use the very old kombucha. That leftover kombucha vinegar can be used as vinegar in salad dressing or instead of wine when making risotto or anything else where you want to add some acidity.

Cloning and sharing your SCOBY

As you keep feeding the SCOBY during your weekly/biweekly kombucha brewing, you will notice that it keeps growing thicker and thicker. At one point, it starts to flake and look like it is two SCOBY stacked on each other. Wait a little longer and soon you will be able to pull the bottom one of. If you wait even longer, it usually comes of by itself. You can give a way this spare SCOBY to a friend (along with some old kombucha tea which they’d need to start a new batch).

If you don’t want to wait, you can also cut a corner of your kombucha and give that away (along with old kombucha), just like you take shoots from plants. Your own kombucha will soon grow over the hole and heal itself while the little offshoot will quickly cover the surface of your friend’s jar.

You can also keep the extra SCOBY in the stack or move pieces to a smaller jar and keep as a backup. Feed them monthly and they will be fine. This is called a SCOBY hotel.

Common questions

• When is the kombucha ready for bottling?
  • Usually after 5-7 days but depends on how many microorganisms you have (~size of SCOBY) and temperature. You can taste some of the liquid. It should be a little sweetness still left
• How long does the 2nd fermentation take?
  • The second fermentation step in the bottle also depends on how many microorganisms you have in the bottle and temperature. In addition, the amount of sugar you add to the bottle greatly impacts this 2nd fermentation. With 2 tbsp per litre, I like to ferment for about 5 days at room temperature (~25C).
  • If you add a lot of sugar, for instance using a fruit pure for flavour, it can go much faster. This means carbon dioxide develops quickly and pressurizes the bottle making it very fizzy (see warning about pressure above and below) before the sugar is consumed, which can make the kombucha quite sweet.
  • If you think fermentation is proceeding too fast, you can let the kombucha ferment in the fridge to slow it down substantially.
• Is it dangerous?
  • With respect to pressure? Can be, see warning above and below. With regard to microorganisms, not really. The low pH kills and destroys almost everything, including botulinum toxins. Make sure you use the back slopping method to reduce the pH for every new batch and submerge the SCOBY. It is supposed to float but also to remain wet.
• Can you get botulism?
  • No. The low pH kills and destroys almost everything, including botulinum toxins. Make sure you use the back slopping method to reduce the pH for every new batch and submerge the SCOBY. It is supposed to float but also to remain wet.
• What is that brown thing?
  • Sometimes dark brown strands form on the underside of the SCOBY. They remind me of algae but they are actually yeast cells clumping together and nothing to worry about. You can leave them there.
• Does this look right to you?
  • The SCOBY changes appearance and can look different and strange when you first start out. Over at HappyKombucha.co.uk, they have assembled a very helpful list of pictures of SCOBYs, highlighting some peculiarities. Check it out if you feel worried.
• How often do I need to feed the SCOBY?
  • When you are making kombucha actively, you can feed the SCOBY and bottle kombucha every 5-10 days or so. Taste the liquid and see if you like it. Can also be drunk as is, without the 2nd fermentation (only used for flavour and carbonation).
  • If you feel like a break, you can leave the SCOBY in its jar for 4-6 weeks or longer. When you’re ready to resume, you just feed it as normal and save the very vinegary kombucha for something else, like you would normal vinegar.
• Can I eat the SCOBY?
  • You bet! While humans can’t digest cellulose, you can still eat it. For instance, you can boil it in simple syrup to create SCOBY candy.

Word of warning about pressure

The generation of carbon dioxide will create a pressure in the bottle (which is how the kombucha gets carbonated). Use bottles that can withstand a pressure. There are bottles that are just for decoration, don’t use those as they can shatter under pressure. I use old kombucha bottles from the store since they are made for this purpose. Also, be careful when you open the bottle. If you’re lucky and the carbonation has developed well, the kombucha will start to fizz and foam and will try to spill over. If you’re unlucky, you might have developed way too much pressure and the cap can shoot off. This happened to our room mate when she was making tepache (a Mexican fermented pineapple/habanero drink which you should definitely try if you haven’t). But be careful. Don’t have your face above the bottle when opening. If you use a very sweet flavour additive, such as pureed fruit, more pressure will develop. In that case, ferment for a shorter period of time and omit the added sugar.

Conclusion

Making your own kombucha is a very satisfying and simple hobby and you get bucket loads of tasty drink. It is also a great introduction to fermentation if you’re not already engaged in this wonderful preservation method. I cannot recommend this enough.

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Kombucha

Making your own kombucha is fun, cheap, tasty and a great introduction into other fermentation projects. You will need a SCOBY to help you but starting your own little symbiotic culture of yeast and bacteria is very straightforward, see instructions in post.

Making kombucha is paired with feeding and taking care of your SCOBY so this recipe details both steps.

Course Drinks

Keyword beverage, drinks, Fermentation, kombucha

Prep Time 20 minutes minutes

Cook Time 10 minutes minutes

Fermentation 5 days days

Servings 1.8 liters

Equipment

• 3-4 L jar
• 2 1-litre bottles that can take pressure (e.g. old kombucha bottles)

Ingredients

Tea for SCOBY

• 1.8 L water
• 2 teabags
• 240 g sugar 300 mL
• 200 mL old kombucha

Flavoured kombucha

• 1.8 L ready kombucha
• 4 tbsp sugar
• Flavour components See notes for suggestions

Instructions

• This recipe uses 2 L kombucha from 'last week' to feed the SCOBY and create flavoured kombucha. If you follow this recipe, in about 1 week you will be ready for a new batch with these same proportions.

  If you dn't have 2L old kombucha, you can still follow this recipe. The important part is to keep 200 mL old kombucha for the SCOBY. You can use anything left after that for your own, flavoured kombucha.

Flavoured, carbonated kombucha

• With clean hands, gently move the SCOBY from its home to a glass bowl.

  It won't dry out during the recipe.
• Set aside 200 mL of the old kombucha for feeding (below). The rest (~1.8 L) is for flavoured kombucha.
• Pour the kombucha into bottles that can withstand a pressure buildup. I use old kombucha bottles.
• Add ~2 tbsp sugar per liter kombucha to each bottle.
• Add your favourite flavouring. I like 1 tbsp grated ginger or 1-2 tbsp mint leaves torn up.
• Seal the bottle(s) and shake carefully, to help the sugar dissolve.
• Store in a dark place for 4-6 days, letting the yeast turn the sugar into carbon dioxide.
• Chill and enjoy.

  Pro tip: buy a little sieve to pour the kombucha through when you serve it. A mini SCOBY can develop in the bottle (perfectly fine to eat/drink but maybe not pleasant). And you might want to filter out that ginger/mint/your favourite flavour.

Brew the tea

• Pour half of the water into a large pot along with 240 g sugar. Bring to a simmer. When the sugar is dissolved, turn of the heat and add the tea bags.
• Let steep for 10 min.
• Discard the teabags and pour into an empty 3-4 L jar
• Pour in the rest of the water.

  This two step water process is a great tip to bring down the temperature faster.
• Wait for the tea to reach room temperature.
• Pour in the 200 mL kombucha from last week you set aside.
• Place the SCOBY back in its refreshed sugar-tea bath. Cover with a breathing material (coffee filter, cheesecloth, teatowel…). Secure with a rubber band and place the SCOBY in a dark place.
• Let sit for ~7 days and then repeat the process for more kombucha.