Guest Posting: Kombucha 101 – Fermentation, by Tadeusz Zagrabinski
In this Kombucha 101 series, Tadeusz writes about the importance of all individual ingredients that are traditionally used to make kombucha. The first part discussed tea. The second part described the varieties of sweeteners. The third part discusses water, and the fourth part the SCOBY. In this final part he discusses the fermentation process.
Now that we have water, tea, sugar, and the culture in place, it’s time to write about the fermentation process.
But before we can ferment our kombucha, we need the right container for that.
If you are a home brewer, this decision is actually quite simple. Most people use glass.
Glass is easy to use and easy to clean. It is also widely available.
Some people use plastic. For us, it’s a no-go. We have covered plastic containers, plastic bottles, and resin (plastic) lined aluminum cans in other blog entries.
Plastics and organic acids just don’t go together. Not even if some governmental organizations consider some plastics to be food-safe (just remember that DDT was also considered safe a while back, and cigarettes were recommended by doctors).
If you are a commercial kombucha brewer, then there are more choices to work with.
Glass is usually considered uneconomical (because of the size and amount of containers needed for larger productions), although some small production brewers still do use glass jars.
We use them, too. We make small individual batches of kombucha (we have 21 different types of kombucha that we carry all the time), and we find glass to be the most neutral vessel for kombucha brewing.
Wood barrels are the next good choice, in our opinion.
Wood has been used for centuries for different fermentation projects. Best Sauerkraut or Dill Pickles came out of wood barrels.
They were and still are used to make wines or vinegars.
So, wood is a proven material for fermentation. It has a character, and it imparts a good energy and sometimes an additional flavor to fermented foods and drinks.
We use a wood barrel to make our kombucha vinegar and in Fall we make an apple vinegar in the same barrel.
We used to know places that brewed kombucha in stoneware crocks.
These are also a good choice, as they’ve been used in different fermentation processes for quite a long time. But they also have drawbacks similar to glass. They are relatively small, and they can be quite heavy. A lot heavier than glass containers.
The most common fermentation vessel for commercial kombucha is a stainless steel tank.
Although volume-wise, they can hold a lot of liquid, they have some drawbacks coming from their specific shape (they are usually taller than wider). These were created for beer and not for Kombucha. So, an oxygenation process is required for better fermentation. But a bigger problem is the possible heavy metal leaching that can occur in an acidic environment (see here).
So, let’s take a look at stainless steel.
What is stainless steel?
Stainless steel is a low-carbon, iron-based steel with other metals mixed in to reduce corrosion and increase strength.
It always contains at least 10% chromium. Other metals can include nickel, manganese, aluminum, silicon, and sulfur.
The combination of metals determines the grade of the stainless steel.(for more, see here.)
Chromium and nickel are heavy metals that are used to make stainless steel. Aluminum can also be used to bond the stainless steel layers (see here.)
We know that some grades of stainless steel are regarded safe for kombucha fermentation, but are they really safe?
Even if that were confirmed by independent studies, stainless steel vessels would never be our choice. Besides, steel carries a cold energy, while glass is neutral.
For us, steel is not a natural choice for any fermentation process, and we like to stick to the materials that are time-proven and that were used for centuries.
So, now let’s return to the fermentation process or processes as actually there are two of them.
At least in the traditional home brewed Kombucha.
First Fermentation Process
First fermentation process (F1), which resembles vinegar fermentation, starts when all the ingredients are in place and when there’s a proper temperature to sustain that process.
The optimal temperatures for kombucha fermentation are between 20-25 degrees Celsius (68-77 Fahrenheit). Lower temperatures between 18-20 (64-68) are also OK. Anything below 18 (64) degrees puts the whole fermentation process in danger. Low temperatures slow down things significantly, and that creates a danger of either some unwanted wild yeasts contaminating the liquid or even molds forming on top of the liquid.
The chance of that happening is even greater when the starter liquid is too weak or when not enough of it is used in proportion to the batch size.
On the other hand, when temperatures stay above 25 (77) degrees, the fermentation process is accelerated, and with even higher temperatures, there’s a danger of yeast overgrowth and the kombucha tasting more like beer. Higher temperatures will also have an impact on alcohol levels.
So what happens during this first fermentation process?
In the first fermentation process, sugar is broken down into glucose and sucrose. When some of that sugar is consumed, alcohol and CO2 are produced, and they become by-products of the fermentation process.
This happens thanks to wild yeasts that reside inside the culture (primarily the ones called Zygosaccharomyces, as they tolerate higher concentrations of alcohol and low pH at the same time).
Next come bacteria (usually Acetobacter or Gluconacetobacter), and they break down the ethanol into acetic acids, giving kombucha a characteristic acidic flavor. Some other bacteria can also be present (like Lactobacillus or lactic acid-producing bacteria).
Here’s the natural carbonation is also produced during F1.
For those who want to know more about kombucha fermentation, there are two online reviews that go into detail about the fermentation process.
The first one is titled Understanding kombucha Tea Fermentation: A Review.
The other is titled Kombucha Tea Fermentation: A Review.
At the end of F1, the amount of sugar is usually greatly reduced, some alcohol is still present, and the amount of caffeine is also lower than at the beginning of the fermentation process.
The length of the whole process of F1 depends mainly on three factors. The initial amount of sugar used temperature, and the size of the batch.
Standard home batches can take from 6-12 days, sometimes even longer when someone likes a very low pH (vinegary) kombucha. Also, when the initial amount of sugar is between 100-150 gr per liter, like in the case of older recipes for medicinal kombucha, it will take a minimum of a week and a half to two weeks for that amount of sugar to be broken down and converted into organic acids.
Lower temperatures will make that process even longer. Much bigger batches, on the other hand, can require three weeks or more.
Unless we are talking about Jun Kombucha. In that case, it’s different.
Honey is used instead of sugar to make Jun Kombucha, and honey gets its sweetness from fructose and glucose. Since these are simple sugars, it only takes about three days for the F1 process to be completed (with batches of 5-10 liters).
Back to kombucha.
When the F1 is complete, kombucha culture is removed, and now two things can happen.
Kombucha can either be strained and filled into bottles, or it can be strained and mixed with additional flavoring agents, like fruits, juices, herbs, etc.
When plain kombucha is already in closed bottles, and eventually the flavored kombucha is also bottled up, it is time for the next process called the second fermentation process.
Second Fermentation Process
The purpose of F2 is to build up a higher level of natural CO2 inside those closed bottles.
Some CO2 will already be present after F1, but that is not enough to have a nice fizz.
Usually, those freshly filled up kombucha bottles are left at room temperature for at least 24 hours.
Depending on the actual temperature of that room and also on the amount of sugar that is leftover in kombucha after F1, that process can take a lot longer.
Kombucha that has been additionally flavored with fruits and sweet juices will carbonate a lot faster, and quite often, it will be unstable, over-fermented, and difficult to open without spilling if it’s not watched carefully.
A more stable and still natural process of F2 can be achieved by letting kombucha build up a nice carbonation in more controlled, lower temperatures, like inside a fridge or a walk-in cooler.
This process can take weeks, but it is more stable.
Sometimes we let our kombucha build up natural carbonation this way, especially in summertime when the temperatures are higher than usual.
We also know of at least one more commercial brewer that is using this method (our friends at GO Kombucha in the UK).
Most commercial kombucha producers skip this method, and they force-carbonate their product with artificial CO2. There are two reasons for that: one is the consistent and controlled level of carbonation in each and every bottle. And the second reason is this: force carbonation stabilizes kombucha to a great extent, as it is written below:
CO2 is used to carbonate soft drinks as well as offering some protection against microbiological growth.(more can be found here)
We always prefer things that are natural, and CO2 is no exception.
Natural CO2 bubbles are milder, and they look different. They never make a person burp after drinking kombucha, which can not be said about other drinks that contain the added CO2.
During this natural process of F2, the amount of residual sugar is also further reduced.
But the alcohol level can increase.
Quite often, commercial kombucha producers do not have much choice but to use force-carbonation, especially when they filter out most or even all the yeasts from their products.
When that happens, a nice thing would be to inform their customers that their products contain added CO2, instead of the natural one, right on the labels.
Unfortunately, that is still not the case with many of those companies.
Maybe the following has something to do with that?
Common sources of CO2 include hydrogen and ammonia production, fermentation, and collection from geothermal wells. Prior to its use, the carbon dioxide must be purified before being considered suitable for its intended use as a direct food additive to the beverage. Potential contamination of a CO2 supply can occur as the result of natural impurities in the raw gas source not being effectively removed, or from gas contamination during storage and distribution.(from the same paper as above)
When kombucha is properly carbonated, it has a nice fizz. Nice, but not excessive.
That means that you are still able to open a bottle without half of its contents spilling all over the floor, or the ceiling, as is the case with many home brewers boasting about their over-excessive carbonation in online videos.
Once the F2 is complete, it is a good idea to put kombucha inside the fridge to cool it down.
Once that is done, kombucha is usually ready to be enjoyed.
But we take our kombucha a step further.
And that brings us to yet another process which we call additional conditioning.
Additional conditioning is a process that we find quite important for our kombucha production.
We produce tea-based kombucha, where the main flavor comes from a specific tea or teas that are used to make that kombucha. We do not use additional flavoring agents.
For us, different teas are like different wines. Green teas, when fermented, can be compared with white wines. Black or darker roasted Oolongs give us results that are comparable to red wines.
We even serve our kombucha in wine glasses. It just tastes better when served this way.
So, over the years, we have noticed that our kombucha tastes even better when it sits inside the fridge for an additional week or two.
During that time, all the flavors blend together, and some of them become even more dominant.
Conditioning that takes longer than two weeks transforms kombucha to yet another level.
Especially the one that is made with some high-quality teas. We aged some bottles, on purpose, for much longer periods of time, and we thoroughly enjoyed them after one year, two years, or even longer.
This past New Year’s, we opened a four year old bottle of our Sanxia Hong Cha kombucha and it was outstanding. Like a delicious and complex wine, sans alcohol. And no, it was not vinegary.
This particular Hong Cha kombucha was bottled in December, 2017.
Now, that almost everything was covered, it is time to enjoy a nice glass of properly fermented, unfiltered and naturally carbonated kombucha, just like ours.
This concludes our kombucha 101 series.
So, cheers and thank you for reading!
This article is from Tadeusz’s Bärbucha Kombucha blog and appears here with his express permission.