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When you first start making kombucha you may be concerned with contamination from pathogenic and other unwanted bacteria and molds which can make your kombucha undrinkable. Although this is a common fear if you maintain your kombucha SCOBY properly you will never have to fear this happening to you.
A kombucha SCOBY is a pellicle formed by acetic acid bacteria, and inhabited by yeast and bacterial species. To maintain a healthy SCOBY keep it between 70-80˚F, a pH below 4.5 and at least 1 cup of sugar per gallon of tea. A healthy culture will form a new SCOBY on the surface of each batch.
Your kombucha SCOBY is an indicator of the health of the various species found in your kombucha culture. Maintaining your culture is not difficult to do with a little guidance.
The purpose of your SCOBY
Your SCOBY is a natural formation called a pellicle. It is made up of mostly cellulose by the acetic acid bacteria found in your kombucha culture. It preforms various functions to help keep your kombucha fermentation healthy.
Acts as a physical barrier from bacteria and mold
Bacteria and mold are everywhere. They are found in the air, on any surface and on dust particles. It is imposable to keep all these invaders from coming in contact with your kombucha.
The SCOBY tends to float on the surface of the kombucha and acts as a physical barrier between the liquid sweet tea and the outside environment. Any bacteria or mold which lands on the SCOBY must be able to survive the harsh conditions of the SCOBY.
Protects from UV light
UV light affects bacteria and yeast species negatively. As the UV light penetrates the cell it damages the DNA of the cell. This affects the yeast by producing mutations in the cell which shorten the lifespan of the yeast. This lowers the yeast cell count and slows population growth necessary for producing the alcohol needed by the acetic acid bacteria.
The bacteria are damaged similarly with the UV light affecting their DNA. This prevents the bacteria from multiplying until the damage is repaired. This again slows the growth of the AAB and LAB found in the culture.
The SCOBY acts to filter the UV light as it travels through the SCOBY. This prevents the UV light from damaging the microbial cells which makes up your kombucha culture.
Helps maintain a low pH in new batches
A new batch of kombucha has a higher pH than a finished batch. This gives mold and other microbial species a chance to grow in your batch. The SCOBY is produced mostly by two species of acetic acid bacteria which keep the pH of it below 4.0. As the SCOBY usually floats on the surface of a new batch any air bourn mold or bacterial species are destroyed due to the low pH of the SCOBY before they can get a foothold in the sweet tea.
Helps to inoculate your new batch
When you make a new batch of kombucha you place your SCOBY onto the surface of the sweet tea from the old batch you just bottled.
When you do this you introduce the bacteria and yeast species which were found in the original batch into the new batch. This is called backslopping and has been done in many forms since fermentation was first discovered.
The yeast is found mostly on the underside of the SCOBY. It looks like a brown layer growing on the surface. If it has been warm and you like your kombucha sweet it may have formed long strand running from the SCOBY towards the bottom of the container.
The lactic acid grow in and around the SCOBY and get included in the matrix of its formation as it thickens.
The acetic acid bacteria are the producers of most of the biofilm which forms the SCOBY and are also found in and around it. Acetic acid bacteria need oxygen to grow so they are found close to the surface of the fermentation.
Why temperature of your kombucha fermentation is important
There are two reasons why this temperature range is best for kombucha fermentation:
Helps the wanted microbial species to grow
The yeast species found in a typical kombucha fermentation grow well in a temperature range of 70-90˚F. Within this range they are very efficient at consuming the sugar in the tea and producing alcohol and CO2. The additional alcohol inhibits the growth of mold.
The bacteria in the culture have an ideal temperature range of 60-80˚F. There are two types of bacteria found in a typical kombucha fermentation, Lactic acid bacteria and acetic acid bacteria. Both or these produce an acid which lowers the pH of the sweet tea rapidly when allowed to grow efficiently. As the pH drops it inhibits the growth of the mold.
Both the yeast and bacterial species consume the sugar found in the tea rapidly at this temperature which lowers the available energy for the mold. This out competes the mold and prevents it from getting a foothold on the tea.
Hinders the growth if mold
Mold has a higher temperature range than the yeast and bacteria in your kombucha. It can grow in temperatures as low as 40˚F although they grow best in the 77-87˚F range. Keeping your kombucha cool provides damp conditions which mold like to grow in. As the temperature is raised the water on the surface of the container evaporates leaving nowhere for the mold to grow.
Why pH of your kombucha is important
Mold growth is inhibited in an acidic environment. It cannot multiply quickly once the pH drops below 5.0 and most mold species cannot tolerate a pH below 4.0. By keeping the pH of your kombucha fermentation low you prevent the possibility of any mold from growing.
This is done by using some of the old kombucha to acidify the new batch. This does two things:
Acidifies the new batch quickly
To prevent unwanted microbial growth you need to maintain a low pH of your fermentation. To do this you add at least 1 part old kombucha to 4 parts new sweet tea. Depending on the pH of the old batch this should lower the pH of your new batch to at least 4.5. If you like your kombucha sweet and only ferment it a short period of time you will need to add more old kombucha into the new batch to ensure this minimum pH value.
If you are unsure how much to add get some pH testing strips and test each batch until you get an idea how much to add.
Inoculates the new batch
This is another form of backslopping. When you add old kombucha into a new batch you are introducing the microbial species which like to live in the liquid of your fermentation. These can be different than the ones which are found in and on the SCOBY.
By adding some of the old culture into the new one you are feeding the culture new sugar and providing a fresh environment for all the species to grow without the hindrance of an acidic environment. This keeps the culture young and active which further reduces the chances of unwanted microbial growth.
Why sugar concentration of your kombucha is important
Everything living needs some type of food. In a batch of kombucha that food comes in the form of sugar. Without enough sugar the culture will not have enough food to multiply rapidly enough to maintain the hostile environment which inhibits mold and other microbial growth.
Mold species are opportunistic and can use a wide variety of things for food energy. They can use simple sugars to grow but they also can break down the bonds in starches to use as energy. The SCOBY is made up of cellulose which are long carbon chains of simple sugars which the yeast and bacteria cannot use for food but mold has no problem breaking these strings down into simple sugar.
Yeast and most bacterial species are unable to break the bonds that hold the simple sugars together which make up starch. Without enough sugar they are unable to maintain their environment to inhibit the growth of mold which makes your kombucha susceptible.
Recognizing a stressed kombucha culture
By watching how your current SCOBY reacts to the fermentation process you can determine the health of your kombucha culture. A healthy kombucha SCOBY can take on several shapes, have different colors depending on the type of tea and be shaped odd but an unhealthy SCOBY is easy to spot.
SCOBY is not very thick after 7-10 days of fermenting
When the new kombucha SCOBY which forms on the top of the container does not get at least ¼ of an inch thick something is hindering the growth of the AAB in your fermentation. When your AAB do not grow as well your kombucha will not acidify as quickly leaving it exposed to unwanted microbial invasion.
Some typical reasons for this are:
- Not enough sugar for the yeasts to convert to alcohol
- Fermentation too hot or too cold
- Mother SCOBY too small
If you are moving from a small container to a bigger container your mother SCOBY may not entirely cover the surface of the new container. This is not a problem as long as the starter tea is properly acidified and the container is covered. The first SCOBY which forms in the new container will cover the whole surface but it may be thinner than normal.
Yeast Strings on the bottom of the SCOBY
Yeast growth is a normal part of making kombucha but when the yeast population gets out of balance several problems can arise.
- The alcohol level goes up. For an explanation of this read How Much Alcohol is in Homemade Kombucha
- The yeast cells consume more of their share of the sugar keeping the pH higher
- Kombucha takes on a yeasty flavor as the number of yeast cells increase
If you notice an abundance of these yeast strings then your fermentation may be too warm. Any temperature above 80˚F will hinder the growth of ABB and LAB but will encourage yeast and mold growth. Also with increased heat the humidity also goes up within the container which encourages mold growth.
Another reason for these yeast strings is short fermetation time, high sugar batches. Yeast species have the ability to multiply in numbers quickly once they reach a certain population. If you provide the yeast in your culture with a high sugar concentration with a short fermentation time the yeast can overwhelm the other cultures in the fermentation.
SCOBY sinks to the bottom
The cellulose which makes up the SCOBY has a density which is slightly denser to that of the starter tea it grows in. This means that it should sink rather than float if all things were equal but because the SCOBY forms a mat which can capture air bubbles it tends to float.
If your SCOBY sits on the bottom of the container it is a sign that the yeast and LAB species found in the bottom of your fermentation are not multiplying and not producing enough CO2. This could be because:
- They don’t have enough sugar to multiply
- The temperature is not high enough
When to dispose of a SCOBY
The only time a SCOBY needs to be disposed of is if it gets infected with mold. This is apparent when discolored spots show up on the top or sides of the SCOBY or the fermentation container. Mold is easy to spot as it is characteristic of mold found on any other food.
The mold can be green, yellow, red or black. It will be fuzzy in appearance and be accompanied by an off smell from the container.
Do not consume any of a kombucha batch with mold growth in it. Once the mold has appeared the batch is totally infected with mold and can cause serious sickness if consumed just like any other food which gets mold in or on it. Throw the whole batch away including the SCOBY as it is completely beyond repair and start again.
Make sure you wash the containter completely with hot water and soap. rince well and let it air dry. Once the container has been cleaned it is safe to start a new batch in it.
Kombucha SCOBY myths
A mother SCOBY is necessary for kombucha fermentation
For all those who want to start making kombucha but do not have access to a mother SCOBY you don’t have to wait. It is not the presents of the SCOBY which makes the fermentation work it is the presents of the various species which make up the kombucha culture. There are several ways to start making it without a SCOBY including:
- Using raw commercial kombucha
- Starting from acidified sweet tea
- Using a vinegar mother
For a full explanation of how th make a SCOBY from scratch check out this article here.
A kombucha SCOBY produces a baby SCOBY
There is no mechanisim which the SCOBY has to duplicate itself. It does not reproduce, multiply, clone itself or any other self-propagating method you can think of. The new SCOBY which forms on the top of a new batch of kombucha is produced by the AAB which are found in the kombucha culture.
This is a totally separate pellicle than the original, although it may be attached in some way it is an original formation. It has the same characteristics as the original as it is produced by the same AAB species as the original.
A kombucha hotel is important to ensuring continuous kombucha
A kombucha hotel is a way of keeping extra SCOBYs which form every time you make a new batch. These extra SCOBYs can be kept in a container with some sweet tea and will continue to house the cultures from the original kombucha batch.
If you decide to keep these SCOBYs you will have doubled your work in making kombucha for no reason. Sure it is nice to have an extra SCOBY for making experimental batches of Kombucha like herbal tea, green tea or coffee kombucha but you can always use the new SCOBY from a current batch in a new batch since you will get a new one with each batch you make.
In the off chance that you lose a batch to mold it is easy to start a new batch without a SCOBY and you will be up and running again in a few weeks.
What to do instead of a SCOBY hotel
SCOBYs are made up of mostly cellulose but also have a wide variety of vitamins and minerals in them from the yeast and bacteria cells which are included in its matrix. This makes them a good addition to your diet once you know how to use them.
Rather than storing unlimited amounts of SCOBYs you can:
- Put them in your smoothie in the morning
- Add them to baking recipes
- Blend them in sauces and gravies
- Make them into creams
- Turn them into candy
If you still have extra SCOBYs then you can feed them to your animals or put them in the compost.