Carr, C. Kombucha Cha-Ching: A Probiotic Tea Fizzes Up Strong Growth. CNBC
News, Aug 9, 2014: http://www.cnbc.com/id/101899262 [accessed Nov
Helm, J. Trendy Fizzy Drink Is Mushrooming. NBC News, April 23, 2010: http://
tinyurl.com/ogy9yyh [accessed Nov 2015].
DiLonardo, M. J. What Are Probiotics? WebMD: http://www.webmd.com/
digestive-disorders/features/what-are-probiotics [accessed Nov 2015].
Beth Nolte is a science writer who lives in Louisville, Ky. Her recent
ChemMatters article, “Going the Distance: Searching for Sustainable Shoes,”
appeared in the February/March 2014 issue.
epithelium—a membrane that covers
the intestines and other organs in our
bodies—to release molecules that go
to the brain through the enteric nervous system, and the brain sends neurotransmitters back to the intestines.
Neuroscientists have found evidence
linking probiotic activity to emotions and
For example, one study showed that
mice that ingested Lactobacillus bacteria
had lower levels of anxiety, stress, and
depression; in another study, anxious mice
whose gut bacteria were replaced with gut
bacteria from fearless mice made the anxious
mice more confident. These results indicate that people with digestive
conditions that cause an imbalance in their gut bacteria might experience mood changes.
So how do yeast and bacteria create kombucha? First, yeast break
down sugar into glucose and fructose, and then it ferments some of the
sugars to alcohol. Then, bacteria oxidize some of the alcohol to acetic
acid (vinegar). For example, one of these alcohols, ethanol (C2H5OH), is
converted into acetic acid (CH3COOH), as follows:
C2H5OH + O2 ➞ CH3COOH + H2O
The bacteria also metabolize some of the sugars
directly to different acids, including lactic acid
(CH3CHOHCOOH). For example, glucose (C6H12O6)
is converted into lactic acid, as follows:
C6H12O6 ➞ 2 CH3CHOHCOOH
As the amount of lactic acid, acetic acid, and other acids rises, the
pH of the solution drops to around
2, which is about the same acidity
level as the human stomach. The
high-acid level prevents the growth
of some types of bacteria, such as
Listeria, Clostridium, and
Salmonella, which are known to cause
food to rot.
The result of fermentation is a
concoction that looks and tastes
both fresh and rotten—and it can create some strong flavors! I make
kombucha by brewing tea with distilled water, adding sweetener (often
sugar), a small amount of fermented kombucha as a starter, and a
culture of bacteria and yeast, called a SCOBY (symbiotic culture of
bacteria and yeast), which you can buy or get from another kombucha
brewer. I use glass containers to combine the ingredients, and let
the containers sit at room temperature. Brewing kombucha at home
requires good laboratory habits—paying attention to the culture,
observing how it looks and smells, and attending to cleanliness is
critical. If it looks or tastes bad, I throw it out.
The fermentation can take about a week. Kom-
bucha concoctions contain a mass of bacteria
and yeast floating on top. Each new batch of
sweet tea causes another layer to grow and the
old growth dangles from the mass in brown
tendrils. Fresh bubbles of carbon dioxide fill
the spaces in between the liquid and culture.
The lactic acid, acetic acid, and other acids
provide a sour taste. It is the tangy taste
of vinegar, similar to apple cider, that not
A growing market
At a retail store, kombucha falls into the category of “functional beverages”—nonalcoholic drinks that contain vitamins, amino acids, and
other nutrients with health benefits. According to SPINS, a company
that analyzes natural-product markets, U.S. sales of kombucha grew
29% in 2013, with more than $122.7 million in revenues from sales. As
kombucha manufacturers start to market flavors that mimic traditional
sodas and package their product in bottles that look like soft drinks,
kombucha is now moving from the health-food section into the regular-food sections.
Kombucha makes me feel great. I enjoy the flavor and love the fizz. I
hear the same from others, but it is still not clear whether this beverage
has health benefits. What is clear is that bacteria have co-evolved with
plants and animals, including us. Bacteria maintain a symbiotic rela-
tionship with us in our
Replenishing the help-
ful bacteria may provide a
boost that improves diges-
tion, but is kombucha the
best way to do it? Kombucha
might help, but scientific
evidence is not available to
support claims that it will cure
everything or even anything.
No single food or drink will fix
an unhealthy system. But who
knows, maybe you will be as
hooked on it as I am!
ChemMatters | FEBRUARY/MARCH 2016 15
The kombucha SCOBY is a mass of bacteria and
yeast. Through fermentation, it turns sweet tea
into a refreshing beverage. The longer the process
goes, the more acidic tasting the brew becomes.
The author samples the kombucha brew, testing it for taste