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When you first start out making kombucha you will have to handle the firm jellylike covering which grows on the top of your fermentation. This is a SCOBY and is necessary for making good tasting kombucha.
A kombucha SCOBY is made up of protein and polysaccharide strands produced by acetic acid bacteria (AAB) found in the starter. AAB produces a biofilm which floats on the surface of the container. In time it forms a thick firm mat occupied by live acetic acid and lactic acid bacterial cultures.
Making great kombucha depends on understanding what your SCOBY is and how it is formed.
The makeup of a Kombucha SCOBY
There are two types of polysaccharides which are found in a kombucha SCOBY.
- Cellulose
- Starch
The polysaccharides come from a number of sources.
The cellulose comes mostly from the yeast and bacteria cells once they die off. The cell membranes of the yeasts are made up of cellulose which the culture has no way to break down. The cellulose is used by the acetic acid bacteria to produce the biofilm which makes up most of the structure of the SCOBY.
Another source of cellulose in the sweet tea are the residue left by the tea leaves. The structure of plants is mostly made up of cellulose which gives the plant its strength. When the tea is steeped micro-particles of cellulose become suspended in the tea which then can be used by the acetic acid bacteria.
The type of sugar also affects the amount of cellulose in the tea. Pure white sugar has been refined to contain only small amounts of cellulose but other types of sweeteners can contain higher amounts. Raw sugar, brown sugar or molasses contain higher amounts of other components including cellulose and starch.
The dominate cultures in the SCOBY prevent the growth of molds which can break down the polysaccharides into simple sugars. Without these molds the culture is unable to efficiently use the cellulose and starches for energy. This leaves these long chain sugars available to the acetic acid bacteria as construction materials for the biofilm which is the main component of the SCOBY.
Only a few bacterial cultures are able to break down the polysaccharides into monosaccharides which are found in the kombucha culture. This is why your SCOBY will continue to grow indefinitely as long as there is enough raw materials to make the biofilm.
The other main component of your SCOBY is protein
The protein comes from the cell bodies which are included in the SCOBY when the yeast or bacteria dies on or in the SCOBY. The proteins are broken down and used as sources of amino acids and minerals for the growth of the cultures found in and on the SCOBY.
Other components include vitamins and minerals. The vitamins have several sources including:
- Tea leaves
- Microorganism respiration
- the sweetener used
The tea leaves which are used to make the sweet tea has a powerful effect on the vitamins and minerals found in the SCOBY as well as in the kombucha itself. Tea leaves contain carotene, vitamin B1, B6 and pantothenic acid.
The three types of microorganisms found in a kombucha SCOBY all produce vitamins for their own use. Some of these vitamins remain in the SCOBY while some make their way into the kombucha.
Yeasts produce a wide variety of B vitamins including B12, acetic acid bacteria make vitamin C in large quantities and lactic acid bacteria also produce B vitamins including folate and vitamin B12.
Depending on the type of sweetener used it can also provide minerals for the culture. If you wnat the most minerals in your kmbucha used sugars which have been prosessed the least like raw sugar, brown sugar or molassis.
Honey can also be used. When honey is used along with green tea rather than the traditional black tea the kombucha is called Jun.
How a SCOBY is formed
A SCOBY is technically a form of a pellicle which is a formation of biofilm produced by bacterial cultures to protect itself from pathogenic bacteria. They are produced by a wide variety of bacterial species. A kombucha SCOBY is produced mainly by the acetic acid A. xylinum.
It forms first as a thin biofilm on the surface of the sweet tea which thickens over time. The cellulose structure has long intertwined strands which interconnect and stretch as the SCOBY grows. As the biofilm thickens other bacterial cultures are included in the structure of the SCOBY which helps it to maintain the cultures viability and robustness.
How knowing the makeup and formation can improve your kombucha making
Understanding the process of how a SCOBY forms is valuable for two reasons:
It helps you support the health of your culture
A healthy growing SCOBY helps to maintain a balanced kombucha culture. A culture which is dominated by one species can give the kombucha unpleasant flavors. You can maintain a balanced culture by evaluating the state of your SCOBY.
The acetic acid bacteria can overwhelm the culture making an overly sour, vinegary kombucha in a short period of time. If your SCOBY is growing fast producing a thick new mat over a short period of time then the acetic acid bacteria may have the upper hand. To reign it in you could reduce the amount of surface area exposed to the air. This gives the acetic acid bacteria less access to oxygen which it needs to grow.
If your SCOBY is thick with many layers it can support a higher amount of acetic acid bacteria so it may be time to divide it. Peel off the top layer of the SCOBY and only use it to ferment your next batch. You can use the remaining SCOBY in a variety of ways. For some ideas read this post about what to do with extra SCOBYs.
When yeasts dominate the culture the kombucha takes on a yeasty flavor and has a higher in alcohol content then you may wish. If your SCOBY has dark spots growing on the bottom of it and/or dark strings are hanging from it then the yeasts may be dominating the culture. This leads to a higher alcohol content because the yeasts can produce more alcohol then the acetic acid bacteria can consume. To fix this you could lower the temperature which you ferment your kombucha as yeasts love the heat but lactic acid and acetic acid bacteria grow better between 20-25 degrees Celsius.
If the lactic acid bacteria get the upper hand then the kombucha becomes overly tart and astringent. Although lactic acid bacteria are minor players in a kombucha fermentation they are still present and can dominate the culture if the acetic acid do not have enough oxygen and the yeast are not warm enough.
When your SCOBY grows slowly but the kombucha acidifies quickly this is a sign that the lactic acid bacteria have the upper hand. Solve this by increasing the surface area of the container or reducing the amount of sweet tea and raising the temperature of the fermentation.
Increasing the surface area will increase the amount of oxygen available to the acetic acid bacteria which will promote their growth. Rasing the temperature will provide needed heat for the yeasts to compete for sugar with the lactic acid bacteria in the sweet tea.
It helps to remove the gross factor
When you first start making kombucha the SCOBY seems gross. It is slimy, rubber mass of semi-transparent snot like material. You will probably not want to touch it but in time you will grow accustomed to it. When you start to collect old SCOBYs in another jar (called a SCOBY hotel) you know you have crossed over.
A kombucha SCOBY is not alien or parasitic it is simply a thickened mass of polysaccharides and protein which acts as a shelter while your kombucha ferments. It preventing mold growth on the surface of the ferment because of its low pH and helps the acetic acid bacteria get enough oxygen to grow by providing a large surface area for oxygen exchange between the liquid and the air.
Is a kombucha SCOBY edible?
Not only is it edible but it is good for you. The SCOBY is full of vitamins, minerals and insoluble fiber. The insoluble fiber helps to feed the probiotics in the gut as well as adds bulk which improves regularity. If you find yourself being overwhelmed with SCOBYs you can use them in a wide variety of recipes from the morning smoothie to sourdough starter.
So if you find a little SCOBY in your kombucha soda don’t worry it is perfectly healthy. You can swallow it, leave it in the glass or filter it out and compost it.