What is Kombucha and how is it created?
Kombucha is a fermented, sweetened tea. It’s a different kind of fermentation than the sauerkraut I demoed in the Viome kitchen previously. Sauerkraut is a wild ferment, where the bacteria naturally present in the vegetable does the work. With kombucha, you add an established culture to the sweetened tea for it to ferment. This established culture is called a “SCOBY,” a symbiotic culture of bacteria and yeast. The yeast in the culture take the sugar that’s used to sweeten the tea and convert it into simpler sugars like glucose and fructose with the help of their enzyme invertase, then convert the glucose into ethanol, water, adenosine triphosphate (ATP–an energy source that supports many processes, such as muscle contraction), and CO2.
Other microbes in the kombucha can metabolize ethanol to make short-chain fatty acids like acetate and lactic acid, which gives kombucha its sour flavor. The microbes also metabolize glucose and fructose to form organic acids like gluconic and acetic acids. They also produce secondary metabolites like B vitamins, flavonoids, and polyphenols theaflavin and thearubigin. These compounds are highly antioxidant and contribute to the color of the tea. Theaflavin is naturally present in black tea and is reddish brown in color. It increases during fermentation but eventually peaks and drops off. Thearubigin is brown in color and increases throughout the fermentation. As it increases, the color changes from reddish brown to light brown, signifying the fermentation is complete.
Hilary holding up a SCOBY from her kombucha ferment
How to make a SCOBY from store-bought kombucha
Select a bottle of raw, unflavored kombucha that contains live cultures. Pour the kombucha into a clean glass jar, ensuring to leave some space at the top.
Prepare the sweetened tea by dissolving 1/4 cup of sugar in 2 cups of hot water, then steep 1-2 tea bags (black or green tea works well) in the sugar solution for 5-10 minutes before removing the bags and allowing the tea to cool to room temperature.
Add the sweetened tea to the jar with the kombucha to provide the necessary nutrients for the SCOBY formation. Cover the jar with a breathable cloth or coffee filter secured with a rubber band.
Place the jar in a warm, dark place (around 68-85°F or 20-29°C) away from direct sunlight, and let it sit undisturbed for 1 to 4 weeks. The SCOBY will initially form as a thin film on the surface and gradually thicken. Once it reaches at least ¼ inch thick, your SCOBY is ready for brewing kombucha.
Watch Hilary’s kombucha demo in the Viome kitchen
Create kombucha right in your home
Supplies
Gallon glass jar
Liquid measuring cup
1 cup dry measuring cup
Airtight glass bottles
Funnel
Strainer
Coffee filter
Rubber band
pH test strips
Note: You can find pH test strips made universally for testing foods like kombucha, as well as soap, or even your saliva. Searching online for a resource will give you many options.
Ingredients
6 black tea bags
1 cup of white sugar
2 cups of starter culture
1-2 cups of flavoring (juice, fresh or frozen fruit, or herbal Infusion)
1 gallon of water
SCOBY
Note: You can purchase starter culture, as well as SCOBY (sometimes in the same package) online from many retailers (search “kombucha starter” on Amazon for some examples). Alternatively, a friend who brews kombucha can also give you a scoby from their homebrew or make your own from store-bought kombucha (see instructions above).
Instructions
Boil 1 quart of water and steep the tea bags for 10 minutes.
Remove the tea bags
Add the sugar, and stir until dissolved
Let the sweetened tea cool to room temperature
Add the cooled tea to the gallon jar
Add starter culture and SCOBY
Top off with water up to an inch or two from the top
Check pH, adjust pH to 4.5 or below with white vinegar if needed
Place a coffee filter over the top and secure with a rubber band
Let sit for one week at room temperature (65-80℉) and away from direct sunlight. At 1 week, start tasting the tea and checking the pH. Once the tea flavor is to your liking and the pH is between 2.5 to 3.5, it is ready for bottling. The fermentation will be slower in a cold room and faster in a warm room.
The liquid should smell tart and slightly vinegary. If the smell seems rancid or if there is fuzzy black or green spots, throw it away. If you suspect something has gone wrong, follow your intuition and start a new batch.
Scoop out and reserve two cups of the tea plus the SCOBY for the next batch. Set aside.
Add juice, fruit, or herbal infusion to the jar. Mix well.
Pour into glass bottles. Cap and place in a dark place.
Check after 3 days if kombucha is bubbly. Once the amount of bubbliness is to your liking, place the bottles in the fridge. Enjoy chilled.
Cheers!
References:
May A, Narayanan S, Alcock J, Varsani A, Maley C, Aktipis A. Kombucha: (2019). PeerJ. 2019 Sep 3;7:e7565. doi: 10.7717/peerj.7565. PMID: 31534844; PMCID: PMC6730531.
Wettstadt, S. (2021, Aug 16). #FEMSmicroBlog. Online at fems-microbiology.org.
