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William C. Beckerson, Ph.D.
Kombucha
What Is Kombucha?
What Exactly Is a SCOBY?
Kombucha is a delicious caffeinated and carbonated drink made by fermenting tea and sugar with bacteria and yeast, which are collectively referred to as a SCOBY! In addition to its wide array of delicious flavors, these drinks also contain important vitamins like C, B6, and B12, acetic acid, lactic. acid, and a small amount of ethanol produced by the yeast. Originally invented in China, kombucha has since spread more widely to various parts of Europe, Russia, and eventually to the entire world!
The word SCOBY stands for "Symbiotic Community of Bacteria and Yeast", which as the name implies is a mutually beneficial cooperation between the common bakers yeast Saccharomyces cerevisiae, and at least two types of bacteria that form acetic acid and lactic acid to give the drink its delicious tangy and sour flavor. These microorganisms work together to form a gelatinous raft at the surface of the drink made primarily out of cellulose and living cells. In nature, these biofilms are made to protect the bacteria and yeast from harsh conditions.
How Can I Make Kombucha?
Kombucha can be made using a 3 step process: Step 1 is all about growing a new SCOBY. The goal for this first batch is not to ferment a product that you can later drink, but instead to allow the SCOBY to form at the surface to the diameter of your container. To start the first step you will need a living culture of kombucha or a cutting of another SCOBY, some sugar, some water, some caffeinated tea, and a container to store it all in. You will also need a breathable lid to help prevent contamination of the tea during the formation of the SCOBY. Cheese cloth and some rubber bands are a commonly used approach.
Because the kombucha has not had enough time yet to grow in the tea, it is most susceptible to contamination during this first step. All future steps will utilize the full grown SCOBY along with some of the previous batch to help cover and acidify new batches, reducing risk of infection. If at any time you notice something fuzzy growing on the surface, this is a sign of fungal contamination and the whole batch should be thrown away. Bacterial contamination can be identified by smelling the drink. Healthy kombucha should smell slightly vinegary and a bit tangy while contaminated kombucha will smell stinky.
Preparing the SCOBY:
4 L of water
200 g of sugar
2 Tbs of caffeinated tea (about 4 tea bags)
250 mL of unpasteurized kombucha or SCOBY
Step 1) Clean a glass container that can hold at least 5 L of liquid thoroughly with a soap and water.
Step 2) Bring 4 L of water to a roiling boil and stir in the 200 g of sugar until fully dissolved.
Step 3) Pour your boiling sugar water into your clean glass container, add your tea, and cover with cloth for 30 minutes.
Step 4) Quickly remove the cloth and your tea, replace the cloth, and let the container cool down, usually overnight.
Step 5) Quickly remove the cloth, pour in your unpasteurized kombucha and/or SCOBY, and return the cloth.
Step 6) Move your covered jar to a dark place at room temperature and let the SCOBY form over 1-4 weeks.
The First Fermentation:
Step 2 is where the fun begins! Once your SCOBY is ready for the fermentation process, new tea can be prepared in the same way as before but this time with a fully formed SCOBY. However, unlike the last time, we will only need to ferment our tea for 5-10 days. During this period, the sugar (dextrose) will act as the starting point for the fermentation process. During the first fermentation, yeast will break down the sugar to form a bit of alcohol (ethanol) through a process called alcoholic fermentation. The acetic acid bacteria in the SCOBY can then convert this alcohol into acetic acid, which gives the drink its tangy flavor; however, while yeast can perform alcoholic fermentation without the need for oxygen (an anaerobic process), the conversion of ethanol to acetic acid requires oxygen (an aerobic process). This is why we cover the jar with a cheese cloth instead of a lid to allow the batch to breathe. It is also important to note that as the yeast and bacteria grow they need a nitrogen source to make amino acids. This is why it is important to use caffeinated tea, as yeast and bacteria can convert the caffeine into essential amino acids. The longer you let your kombucha ferment, the less sweet and more tangy it will become.
The Second Fermentation:
The 3rd and final step in the process is where our culinary creativity comes in to play, as this is the step where we will add the various flavors for our drink! To do so, we will require some air-tight bottles. Flip-top bottles like the ones in the picture below are commonly used for this step to help seal the bottle. Sealing the bottle is important for this step for two reasons. 1) will create an anaerobic environment in which the lactic acid bacteria in our SCOBY can thrive, breaking down the sugar from the flavoring ingredients into lactic acid, making the drink sour. This is also how sour beers are made! And 2) sealing the bottle will allow for the carbon dioxide produced by fermentation to build up, naturally carbonating the drink! Just like in the first fermentation step, this process can also be performed anywhere from 5-10 days depending on how sweet or sour you want to make your drink. During this time, it is VERY IMPORTANT that you periodically open your bottles every couple days to slightly to let some of the air escape, a process called burping. If you don't burp your bottle, you run the risk of them exploding due to pressure build up!
Step 1) Remove the SCOBY and some of the liquid to a new sterilized jar and keep it for future batches.
Step 2) Prepare your flip-top bottles by adding about 1/2 Tbs of sugar and your favorite combination of fruits or other flavorings.
Step 3) Stir the kombucha well and use a funnel to pour the kombucha into the flip-top bottles.
Step 4) Mix the bottles well and store in a dark place.
Favorite Recipes To Try!
1) Orange peels and ginger
2) Fresh strawberries
3) Apple slices and cinnamon sticks
Fun Fact: The fruits your add to your kombucha will have their own natural yeasts and bacteria that can contribute to the fermentation.!Ginger in particular is well known for it Lactobacilli that help with carbonation.
The Health Benefits and Risks of Homemade Kombucha
Because unpasteurized kombucha contains living microorganisms that are commonly found in the gut microbiomes of humans, kombucha is thought to help promote our overall gut health by supporting digestion and improving our immune system functions, much in the same way that yogurt and other probiotic foods do. However, while there are some studies that support these claims, drinking large amounts of unpasteurized kombucha has also been linked to disorders like metabolic acidosis and liver damage. It is also important to recognize that any time you prepare unpasteurized drinks you run the risk for food poisoning due to contamination of the beverage with other types of bacteria or fungi. While the acidification of the drink during the fermentation process and the presence of the SCOBY help prevent contamination of the batch by other foreign bacteria and yeast, contamination is still possible, particularly in the early phases of the first fermentation. It is therefore recommended that people with compromised immune systems avoid drinking unpasteurized kombucha to prevent dangerous infections. It is also VERY important that you do not attempt to substitute the sugar for honey, particularly for the first fermentation step. This is because honey can contain Clostridium botulinum, the bacteria capable of producing neurotoxins that can cause botulism, a potentially deadly illness!
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