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The Science Behind Kombucha Brewing

kombucha brewing bannerBrewing kombucha at home is becoming popular as a hobby as people are increasingly becoming more aware and concerned with their health and wellness.

If you're interested in brewing your own version of this fermented tea one of the most important things to keep an eye on (as with any fermented food or beverage) is the pH level. This might sound like a lot to a new kombucha brewer, so we've put together all the information a new brewer needs to make a safe and healthy kombucha at home.

What is pH?

In technical terms, pH is the hydrogen ion activity in a solution. It’s measured on a scale of 0 to 14, with 7 being neutral. pH is one of the most important analytical tests in kombucha brewing. Proper pH not only makes sure your kombucha tastes and looks good, but also ensures that it is safe to drink.

pH scale

What is kombucha?

Simply put, kombucha is fermented tea made with tea, sugar, bacteria, and yeast. A bacteria culture called a SCOBY mother (Symbiotic Culture of Bacteria and Yeast) is added to steeped tea and sugar. Records of people making kombucha date as far back as China in 220 BCE during the Tsin Dynasty. The drink gets its name from Doctor Kombu, who is said to have brought the "tea fungus" from Korea to Japan in 414 CE.

While the debate on the curing properties of kombucha is ongoing, it is indeed full of beneficial probiotics and acids. A serving of the popular brand GTs Enlightened Organic Raw Original Kombucha gives you 20% of many daily B vitamins and 25% of your folic acid. This particular kombucha contains antioxidants, organic acids, and over 1 billion probiotic organisms.

Hanna Note: The Center for Disease Control and Prevention (CDC) recommends a daily limit of kombucha of no more than four ounces.

The idea behind drinking kombucha is that it results in a happier and healthier gut, aiding in digestion, nutrient assimilation, and detoxification.

What is a SCOBY?

kombucha scoby

As mentioned above, SCOBY stand for Symbiotic Culture of Bacteria and Yeast. This gelatinous, cellulose-based biofilm is made up of multiple bacterial and yeast species including Acetobacter and Saccharomyces types. 

Much like beer, the bacteria and yeast breaks down and convert the glucose in the sugar to ethyl alcohol and carbon dioxide gas in a process called fermentation. This produces a tangy tea beverage with a very low alcohol content, usually below 1% ABV.

The SCOBY "mother" will produce "daughters" with every brew, forming new layers on the surface of the liquid. These can be left to thicken the SCOBY or can be divided and stored in a "hotel." A SCOBY hotel is a collection of spare cultures that can be stored with some kombucha starter liquid to use if your active culture gets spoiled, for starting another batch of kombucha, or to share with friends.

[DOWNLOAD] pH MEASUREMENT GUIDE

Why pH is important in kombucha brewing

Black tea, the most common type of kombucha tea, should read at about pH 4.9. This of course depends on the brand of tea and its brewing strength; the stronger the brew, the more acidic it is. Kombucha can also be made using green or oolong tea.

You should take your first pH reading when you have steeped your tea and added the starter tea (with your SCOBY). By adding previously fermented kombucha, or starter liquid, you are rapidly decreasing the initial pH of the mixture to prevent any early microbial contamination. At this point, your first pH reading should be below pH 4.6.

After this, you should leave the kombucha to ferment at room temperature for 7-10 days. Once primary fermentation is complete, the raw unflavored kombucha should have a pH reading anywhere from pH 2.5 to 3.7; the higher the pH, the sweeter the kombucha will be.

With that said, it’s important to know that your kombucha has not completed fermentation at this point. The fermentation process remains active in both an anaerobic environment (without oxygen) and at colder temperatures, just at a much slower pace. So once your kombucha is bottled and refrigerated, it will still continue to ferment. If you add any fruit or herbal flavorings, this may also influence the rate of secondary fermentation as the microbes feed off the new sugars.

kombucha bottles and scoby

Monitoring pH is important when brewing kombucha, not so much for taste, but for identifying when the kombucha is protected from harmful microorganisms. Since the purpose of brewing kombucha is to develop more good bacteria, it's important that the pH of the kombucha be low enough to act as an antimicrobial solution to prevent the growth of bad bacteria. 

According to the Food and Drug Administration (FDA), foods with a final reading between pH 4.6 and 2.5 are safe for human consumption, because the low pH prevents microbial spoilage. It's important to use common sense and clean equipment when brewing kombucha – if there is mold on your SCOBY, it's time to start a new batch.

Testing your kombucha brew's pH

The easiest way to measure pH is with pH test strips or a pH meter. However, while inexpensive, pH strips are subjective and based on the interpretation of color. Litmus paper only provides the general pH range and can become contaminated, which leads to inaccuracies.

To be sure that the kombucha you are brewing is safe, it's best to use a pH meter with digital readout. Digital pH testers take out the guesswork, so you can be confident that your homemade kombucha is in a safe and healthy range.

Checker® Plus Digital pH Tester

HI98100 Hanna Checker PlusThe Checker Plus pH Tester is a pocket sized pH tester that is ideal for any budgetWith a one button operation, replaceable pH electrode, large LCD screen, and easy automatic calibration, this handy economical meter is the perfect device for testing your kombucha brew.

The long, tapered  probe allows you to test the pH of your kombucha without disrupting your brew as you slide it past the SCOBY.  The replaceable electrode extends the life of your Checker, and the automatic shut-off ensures a long battery life. You can be absolutely sure that your kombucha is safe to share and drink with increased digital resolution.

 

Tiffany Fredette

Written by Tiffany Fredette

Tiffany graduated from The University of Rhode Island with a degree in biology and wildlife conservation. With a history of environmental and medical research, she uses her technical knowledge to write content for Hanna Instruments. Tiffany may be reached at tfredette@hannainst.com.

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