Kombucha
Introduction
For me, kombucha defines home fermentation. And nothing is more simple and versatile. This soured, lightly carbonated beverage is traditionally made from a sweetened tea and has been fermented by humans since around 200BCE. It began it’s domestication of people (as all good fungi does, read Entangled Life for more info) in Manchuria, now northeastern China, where it spread east to Japan. The success of kombucha is largely attributed to the efforts of a legendary Korean physician called Kombu, hence the name (cha means ‘tea’ in Chinese).
Until very recently, kombucha remained a beverage enjoyed by those who lived in Japan, China, Vietnam, Korea and the eastern side of Russia. But thanks to clever marketing and a growing awareness around the health benefits of probiotics and unfiltered ferments, kombucha has exploded in popularity across the entire world. Today, you can even order a scoby online and it will arrive in the post, ready to start metabolising your tea and producing new scoby. Almost any liquid (with a little sugar added) can be fermented into kombucha. So once you’ve had fun making this basic kombucha recipe feel free to explore infusions that include some of your favourite garden herbs and fruits.
I like to use kombucha as an elegant alternative to alcohol. It hits all the same notes with far less inebriation. From herbal infusions, floral blends, tree sap, or fruit juices, it is possible to make kombucha that pairs with literally any food you can think of and I believe it has far more flexibility than any other drink. And thanks to it’s sugar content, it is possible to reduce a large batch down into a fermented sweet syrup to use in cooking as a glaze, topping or dressing. You can even allow it to ferment far beyond the stage of a palatable drink and into the realms of vinegar as another tool for cooking. At this stage, kombucha can replace white wine or malt vinegar in a recipe for an interesting and enjoyable spin on traditions.
If you’ve drank store-bought kombucha and you’re thinking of making your own from this recipe, brace yourself for a whole world of flavour. At home we can produce a drink with much more subtle and nuanced, with complex layers of bitter tannics and floral honey. So let’s introduce you to your scoby.
You may often hear the terms ‘mother’ and ‘scoby’ used interchangeably because the term ‘mother’ is used broadly in fermentation where an organism or colony is used to kick start new batches. However, in kombucha it is technically only ever a scoby (Symbiotic Culture of Bacteria and Yeast). Kombucha is the liquid produced during the fermentation, the scoby is the floating jellyfish-looking thing that turns the tea into kombucha. Yes, it may be ugly, but that blob is alive and wonderful and here’s why.
Details on SCOBY Activity
Specific species of microbes may vary from scoby to scoby, but broadly speaking they consist of two main types. Acetic acid bacteria (AAB, which in most cases is Gluconacetobacter xylinus), which forms the structure of the scoby (the pale jellyfish raft that is actually called a zoogleal mat and is made from the excreted cellulose of the bacteria) and a yeast (often Saccharomyces cerevisiae, a unicellular fungus) which makes up the darker coloured growth on the layers of scoby and often sediment that sinks to the bottom of the jar. But the beauty is how they work together. The yeasts of the scoby metabolise the sugars in the liquid into ethanol and carbon dioxide (in a very similar process to beer, wine, and spirits) but the AAB then ferment the ethanol by oxidizing it into acetic acid, utilizing oxygen from the environment. This is why kombucha is never as alcoholic as wine or beer, but always remains between 0.5% and 1% ABV (alcohol by volume). The average beer is around 5% and wines tend to be around 12%-14%. Under ideal conditions, the yeast ferments 2 units of sugar into 1 unit of alcohol and the AAB converts 1 unit of alcohol into 0.9-0.95 unit of acetic acid. This type of relationship is observed across all of nature; the microbiological cultures that live in our fermented foods, garden soils, the air we breath, the water we drink, and even our skin and gastrointestinal tract (which our immune system learns to incorporate as a type of ‘foreign organ’ i.e. a crucial element of bodily function that collectively shares no genetic material with us, it’s host, within the first two weeks of life). At one end of this spectrum we see parasites and pathogens, at the other end are mutualists like the scoby and our gut biomes. In the case of a scoby, the yeast is granted housing within the bacteria’s colony and provides the ethanol the bacteria feeds on. In turn, the bacteria produces an acidic environment that both can tolerate, protecting them from unwanted pathogens and intruders. This is a similar process to how vinegar is made except vinegar is a two stage fermentation. In kombucha, both elements (ethanol and acetic acid) are fermented simultaneously. In vinegar, yeasts are allowed to do their job of converting sugars into alcohol until either the alcohol level is high enough to kill them off, or the person making it chooses to interrupt the process through pasteurization. This results in wine and beer. The second stage introduces AAB to the alcohol to convert the ethanol into acid. In this instance, your fermentation is controlled by the tolerance the initial yeast has to the alcohol it produces and therefore how much ethanol is leftover for the AAB to convert. In kombucha the fermentation is sustained as both sides of the ferment continue for as long as their is sugar to metabolise.
That’s where we enter the equation. It’s up to us when we stop a batch of kombucha from over fermenting. We taste test it each day to make sure the balance of sweet and acidic is still pleasant and allow it to grow more and more acidic until it has reached the desired flavour. That’s when we harvest the liquid and prepare a fresh batch for our scoby to begin fermenting. The yeasts get more sugar, the AAB more ethanol, and the human more kombucha. That’s why I said that it was the scoby who domesticated us. Without us serving it’s needs it would die once it ran out of food, but our roll in this three-way symbiosis is to keep the supply chain running. In fact, it is believed that before the times of microbiology, people thought the best indicator of a healthy scoby was a thick and buoyant raft. These were prized amongst kombucha makers who would trade and cultivate the best specimens and give precedence to the bacteria that were able to produce them. Anybody who has left a bottle of unpasteurised kombucha ambient for too long will tell you that the microbes that make kombucha don’t require a zoogleal mat at all, but because of our intervention most now produce thick rafts.
Much like rings on a tree, we can observe the history of a scoby by the activity of it’s layers. Many thin layers means periods of inactivity, whilst one or two thick layers are a sign of high activity, as a result of lots of sugars. But there is an optimum sugar level for kombucha, as too much sugar actually acts as a preservative. The sugar content of something is measured by the amount of dissolved sucrose and referred to as it’s Brix (Bx) content. High enough Bx level shocks microbes and kills them, which is actually a defense that a lot of plants and animals use against spoilage found throughout nature. Honey, which is usually around 82% sugar, never goes off. And healthy plants have a much higher Bx level than their sickly counterparts, making them harder for microbes and insects to digest (survival of the fittest, but not how we usually think of it). So what is the perfect amount of sugar for a scoby?
Sugar Ratio and Temperature
The answer, like much of life, is moderation. If we start a batch of kombucha with a high level of sugar (35Bx), then the scoby will quickly turn the drink far too acidic. But if we start with a Bx level of 12, the scoby ferments at a pleasant rate and produces a delicious kombucha. This roughly equals 240g of sugar to 1.75kg of water (I always weigh ingredients when working in fermentation or baking).
The next question is how long? Generally, ferments tend to work in an arch. To begin with they don’t do much, gradually setting to work converting sugar. Towards the middle of the cycle the activity picks up before quickly peaking and rapidly going past the point of deliciousness. This is where practice comes in for the home fermenter. As temperature plays a critical role in the cycle, you need to pick a room with the most stable temperature night and day. I keep my scobys at 20C/68F and they’re perfectly happy (take a moment to imagine one looking happy, smiling and bubbling away). At this temperature, they take between 10-14 days to ferment a pleasantly acidic kombucha. After 6 days I taste test it each day to make sure I don’t miss the sweet spot. The prime temperature to keep a scoby at is 28C/82F. At this temperature a batch of kombucha is ready in roughly 7 days.
At this stage, I either bottle it fresh into sterilized bottled or freeze it, but I never pasteurise. To heat such a delicately flavoured fermentation can destroy a lot of the nuance and hard work of fermenting a kombucha in the first place, so freezing it when it reaches the perfect level of sweetness and acidity is the best way to halt the process and preserve the flavour. Another factor to consider in the flavour of your kombucha is the flavour of your scoby. It might sound silly, but scoby take on the flavour of the liquids they ferment, resulting in a type of living library of flavours. If you used a scoby to make a batch of plum or berry kombucha, then put that scoby in a batch of lemon or nettle kombucha, it will flavour the next batch with a considerable amount of the previous ferment. In this regard, if you plan to make different flavours of kombucha, I suggest keeping a scoby in a neutral jar (sugar water), and harvesting fresh scoby from it whenever you want to start a new flavour.
Backslopping
Another important step to take in looking after your scoby is backslopping. This highly unattractive word is the name of the process where we prime a fresh batch in preparation for the scoby. If we put a scoby into a freshly brewed and cooled tea it will get to work metabolising the sugars and raising the acidity of it’s new environment. However, there is a window of time where it remains vulnerable to unwanted pathogens and infection whilst the liquid isn’t acidic enough to protect it, so we take a small percentage (10%) of the previous batch of kombucha and add it to the fresh along with the scoby. This is the blackslopping process. By doing so, we lower the pH enough to kickstart the scoby’s protection and give a health dose of yeast and bacteria that live in the liquid of the previous batch. It’s a system used in a lot of alcohol making.
Dividing SCOBY
As your scoby is moved from batch to batch you will notice is getting larger and larger. This is a natural growth as the colony feeds but not necessarily good for kombucha flavour. Large scoby will acidify your drink much quicker. The ideal size of scoby to kombucha is one that sits across the surface of your liquid with about 2cm of growth below. The darker coloured layers below are older and less effective at fermentation, so if you decide to divide or trim your scoby, it is the older layers you should remove and the lighter coloured new layers you should keep for the following batch. To do this, you can often pull the layers apart by hand, but if you find the layers of your scoby are particularly thick you may need to use a sharp knife.
Alternative Infusions
Finally, if you plan to experiment and try infusions of ingredients you might not have looked into before, bare in mind that a lot of plants produce naturally antifungal or antibacterial qualities. These damage or hamper the scoby’s ability to metabolise and will either slow the process or kill the colony altogether. So if you’re experimenting, I’d suggest keeping a main scoby and producing secondary scoby for experiments. You can do this by dividing scoby from an old one, or by adding a little sugar water to an old batch of kombucha after you’ve removed the scoby from it. This will ignite a fresh fermentation from the yeast and bacteria still in the liquid and cause a new scoby to begin appearing at the surface. After a couple of weeks, this scoby will be thick enough to handle and move into a new batch of kombucha. For further suggestions, see the bottom of this page.
Storing your Scoby
If you don’t plan to regularly make kombucha, you can store it in what is commonly called a ‘scoby hotel’. This just means that you keep it in a batch of sugar water and you allow to ferment far beyond the palatable range of acidity. In this solution, your scoby will happily wait until you need it again for 2-3 weeks at 20C / 70F or two months if kept cooler (16C / 60F).
Basic Kombucha Recipe
Drink / Fermentation
1.7ltrs water
250g sugar
200ml unpasteurized kombucha (backslop from a previous batch)
1 scoby
8 teabags
Equipment: 2.5litre jar, a measuring jug, a kettle, a plate, steel funnel, 2ltrs worth of glass bottles, caps, bottle capper and spoon. All sterilized. A muslin cloth and elastic band.
Step 1.
Boil 300ml of the water and add the sugar and teabags. Sugar dissolves in water at a ratio of 1:1, but here I have increased the ratio slightly to increase the exchange with the teabags. Stir the water until the sugar has fully dissolved, then allow the tea to infuse for 10 minutes.
Step 2.
Remove the teabags and add the remaining cold water to lower the temperature of the liquid to a manageable level for the scoby. Pour it all into the jar you plan to ferment the kombucha in, then add the backslop from the previous batch and the scoby. If you are moving a scoby from one batch to the next, store it on a sterilized plate whilst between jars.
Once everything is in place, fasten the muslin cloth in place and put the komchuba out of direct sunlight on a clean shelf where it can remain at ambient temperature.
Step 3.
Keep an eye on your scoby and make sure it doesn’t dry out where it pushes itself out of the liquid. If this happens, remove the cloth and use a sterilized spoon to gently push it down, allowing the liquid to wash back over it. If it is left for a number of days to dry out it may become vulnerable to infection.
After a week, begin taste testing it and when it reaches the desired level of sweet/acidic, prepare your bottles and plate by sanitizing them with boiling water or alcohol. Start your next batch of sweet tea whilst you allow the equipment to air dry, then remove your scoby with cleaned hands and place it on the plate for the next batch.
Filter your kombucha through a boiled muslin cloth into your bottles and cap them before storing them in a refrigerator. Be sure to keep 10% spare for the following backslop and start your fresh batch of kombucha off right away (try not to leave your scoby on the plate for too long or it will dry out).
Your kombucha will keep for 10 days in the fridge or 3 days after opening. It should sparkle when opened as a second fermentation will take place in the bottle (much like Champagne), producing carbon dioxide bubbles. Take this into consideration when tasting your kombucha if you are sensitive it it’s acidity. Alternatively, you can freeze your kombucha to preserve it for longer, or simmer it over a low temperature in a saucepan to make kombucha syrup for cooking, glazing or salad dressings (which lasts months in the fridge).
Further Experiments
Try infusing herbs from the garden (roughly 200g will replace the tea bags used in the recipe above). Add the fresh herbs to the hot water/sugar solution and let them stew for 10 minutes. Pass the liquid through a fine mesh sieve and follow the rest of the recipe above as normal. Bare in mind that some plants produce antifungal and antibacterial chemicals that could slow down or halt the fermentation of your scoby. When experimenting with something new, separate a piece of your main scoby and use this in case you accidentally kill it.
When making a flower infusion, dissolve your sugar into the boiling water, then cool it down by adding the remaining water before you add your flowers. A lot of flowers have delicate flavour compounds that are easily destroyed by heat, so once you’ve chilled your sugar water, add the flowers and blend it for 30 seconds. This will break the flowers up and disturb the pollen (where a lot of flavour comes from). Leave the mixture in the fridge for 12-24 hours to allow it to infuse before passing it through a fine mesh sieve and continuing with the recipe.
Fermented kombucha syrup. After fermenting a batch of kombucha (or if you’ve accidentally over fermented it and it’s become far too acidic), pour it through a sieve into a saucepan. Place this on a low to medium heat and simmer to reduce. This may take time but don’t be temped to turn up the heat as you will destroy a lot of the nuanced fermented flavour. Once the liquid has reduced to a stage where it appears thicker (like a maple syrup or honey), pour it into a sterilized jar and keep in the fridge. I have never known a kombucha syrup go off and I’ve stored them for over 6 months.
You can also use agar to make your own kombucha jelly. The normal ratio for agar is 0.9g of agar powder/1g of agar flakes for 100ml of liquid, however, for an acidic liquid we need a little more, so for kombucha we require 1.3g per 100ml. This works better for a flavoured kombucha like fruit juice, but is particularly enjoyable if the kombucha is sweetened or reduced before setting. To set a kombucha with agar, measure how much agar you will need, then whisk it into your cold kombucha. Put it on a medium-high heat (it needs to reach 90C / 194F) and when it begins a rolling boil, hold it there for 8 minutes. Pour the liquid into the container you wish to set it in and cool it in a bath of water or a colder room. Unlike gelatin (which cannot set acidic liquids and need refrigerator temperatures to set), agar will set at room temperature (anything below 35C / 95F). This recipe loses some of the more subtle flavours of kombucha but is still great fun and a nice, acidic answer to normal jelly.
Lastly, you can freeze your kombucha for storage or you can freeze it into ice cubes for uses in cocktails. It gradually releases acidity as it melts, balancing sweet drinks in a pleasantly refreshing way.