The Science Behind Kombucha Brewing: pH & Titratable Acidity

Kombucha-Brewing If you have stepped inside a health food store, craft brewery, or even a local convenience store in the last 10 years, chances are you have encountered a bottle of a slightly fizzy, fermented tea known as kombucha. Whether or not you have personally braved a sip, this ancient drink’s popularity has boomed in the last decade, popping up first on the West Coast and spanning across the United States as consumers become more aware of its proposed health benefits. While studies have suggested that health benefits linked to kombucha have at times been inflated by popular media and industry leaders, kombucha is still thought to be a rich source of probiotics, organic acids, and antioxidants.

If you are interested in brewing your own version of this fermented tea, a few critically important things to keep in mind are pH and titratable acidity. Depending on your familiarity with some of these parameters, this all might seem a little intimidating, so we’ve put together all the information a new brewer (or seasoned hobbyist) needs to make safe and consistent kombucha.

What is kombucha?

First brewed in China around the year 220 BC, kombucha in its simplest form is a fermented tea made from combining tea, sugar, bacteria, and yeast. After the tea is steeped and sugared, a culture commonly known as a SCOBY (Symbiotic Culture of Bacteria and Yeast) is added, allowing fermentation to begin. After 7 to 10 days, the tea has become an acidic, slightly carbonated, and somewhat alcoholic beverage hailed for its supposed healing properties for ailments ranging from high blood pressure to Type 2 diabetes.

Kombucha made its way across Europe in the early 1900s going by many different names – “Kambucha” in Russia and “Kombuchaschwamm” in Germany before coming to the United States in the mid-1990s where George Thomas Dave unwittingly launched the industry by selling his homemade teas into local health food stores. Today his brand, “GT’s Living Foods” still leads the industry accounting for roughly 40% of the US Kombucha market. In 2021 the North America Kombucha Market size was valued at approximately $357M and is expected to reach $1066M by 2026

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?

SCOBY

As mentioned above, SCOBY stands 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. SCOBY when nurtured in the correct environment will continue to grow feeding off sugar sources in the tea as its fuel.

Similar to the fermentation of beer, the yeast in SCOBY work to break down the fermentable sugars in the tea, producing ethanol and carbon dioxide. Following this, the bacteria from the SCOBY convert the ethanol into organic acids, like acetic acid. During this fermentation process, not a lot of sugar is left behind and most of the sucrose initially introduced to the tea during steeping is broken down into fructose and glucose. This process produces a tangy tea beverage with exceptionally low alcohol content. To be considered a nonalcoholic beverage and to comply with FDA regulations, kombucha must have an ABV of less than 0.5%. Kombucha with an ABV 0.5% or greater is an alcoholic beverage and must comply with TTB regulations.

Following each brew, the SCOBY "mother" will produce "daughters" with every brew, forming new layers on the surface of the liquid. These can be left to thicken on the SCOBY for future use or can be divided and stored as a separate culture if your SCOBY "mother" is ever contaminated or compromised. Maintaining a fresh and healthy SCOBY is critical as SCOBYs are used to help kickstart fermentation in new batches of kombucha, rapidly decreasing pH and helping to set the production of ethanol and carbon dioxide in motion.

What is pH and Why is it Important in Kombucha Brewing?

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 you produce a consistent kombucha batch to batch, but also it ensures that your kombucha is safe to drink

When brewing kombucha, you should test your pH at a minimum twice during the process: once at the beginning of fermentation and again when the fermentation is at its completion. If utilizing black tea, one of the most common kombucha teas, the starting pH of steeped tea should read between 4.9 to 5.5 (although factors like brew strength and tea brand can have a strong influence on this value.) Other varieties of kombucha may utilize green tea or oolong tea which usually range in 4.9 to 5.5 and 5.5 to 7.0 pH, respectively. In general, the stronger the brew, the more acidic it is.
Upon combining the SCOBY with steeped tea, there should be a somewhat rapid decrease in pH. By adding previously fermented kombucha/starter liquid the SCOBY is stored in, decreasing the initial pH of the mixture is key to preventing early microbial growth/contamination. At this point, pH values should read below 4.6. If pH values are 4.6 or above at this stage, it’s recommended that more starter liquid be added to lower the pH and bring it to a safe level.

After this, kombucha is typically left to ferment at room temperature for a period between 7 to 10 days. When primary fermentation is complete, the raw, unflavored kombucha should have a pH reading anywhere from pH 2.5 to 3.5. To spot-check the progress of your initial ferment, it’s recommended to begin testing pH around Day 7. The FDA recommends that if pH values have not reached ≤4.2 by the 7th day of fermentation that the kombucha be discarded as the SCOBY is likely contaminated or the fermentation was kept too cold.

With that said, it’s important to know that 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 even once kombucha is bottled and refrigerated, it will continue to ferment. If any fruit or herbal flavorings are added, this may also influence the rate of secondary fermentation as the kombucha continues to feed off newly introduced sources of sugar.

Monitoring pH is critically important when brewing kombucha, not necessarily for taste (more on this later,) but for identifying when the beverage is protected from harmful microorganisms. It's important to use common sense and clean equipment when brewing kombucha – if there is mold on the SCOBY, it's time to discard and 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 a 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.

Quick and Portable Testing Option

The Wine pH Tester is engineered to solve the challenge of measuring the samples with a high solids content. The built-in probe features a glass body, spherical tip, and Hanna's Clogging Prevention System (CPS) that resists clogging 20x longer than a standard ceramic frit. This tester calibrates to the 3 buffer which is better suited for kombucha.

What is Titratable Acidity and Why is it Important in Kombucha?

Fermented-kombucha-probiotic-drink

After all this talk about pH you might be wondering what else we could need to know about acidity. It’s important to realize though that pH is just one piece of acid analysis in foods and beverages, it is more responsible for ensuring food safety and microbial stability than sensory profile. For guaranteeing a tasty brew, titratable acidity is a more appropriate analytical measurement.

While pH tells you how acidic your kombucha is, titratable acidity (TA) is a measurement of the actual acid concentration in food as an approximant value, determined by either manual or automatic titration. Understanding acid content in your brew can enable you to quantify the sensory attributes of your brew, such as its tartness and tang that pH alone cannot.

While it’s easy to associate pH and TA together, it’s important to remember that there is no predictable correlation between these two. For example, two juices can have the same titratable acidity with very different pH values. While there can be multiple acids present in kombucha like lactic, acetic, ascorbic, and gluconic, usually the dominant is acetic acid. As a result, TA values are expressed as grams of acetic acid per liter of kombucha.

Beyond its benefits for sensory, some leading kombucha brewers have used titratable acidity as an indication for fermentation completion alongside pH. By tracking acid concentration during the fermentation period rather than pH alone, the slowing of acetic acid production indicates lower amounts of fermentable sugars still present in the matrix. While it is still critical that pH values are lowered to FDA recommended ranges for safety reasons, understanding when TA values begin to level off helps brewers establish batch-to-batch consistency, ensuring a consistent and pleasant sour is maintained with each batch. Some popular kombucha publications site 4.0 to 4.5g/L acetic acid as an optimal TA range, however, this can vary dramatically from brewer to brewer dependent on preferred sensory profile.

Hanna's HI931 Automatic Potentiometric Titrator

Designed with lab footprint and space optimization in mind, the HI931 is a compact titrator to meet your dedicated testing needs. Methods are customizable and can be optimized to your specific sample. Track your progress via a real-time titration curve and log each analysis with a fully customizable report for seamless data filing. Designed with user experience in mind, the virtual keys present on colored display are intended for quick and easy navigation between screens and even come with a dedicated help button. The HI931 also comes backed with a committed team of Hanna Application Engineers and Technical Support ready to help you to get up and running in addition to supporting you throughout the lifecycle of your titrator.
For more information surrounding Automated Titration, check out our blog post Top 5 Reasons Why You Should Move to Automated Titration.

What Now?

Now that it is clear how a better understanding of pH and TA can help take your kombucha brewing game to the next level, we at Hanna are ready to help equip you with any testing instrumentation you need. We hope that you enjoyed reading, and we look forward to chatting with you on any kombucha and/or testing topics.

Got Questions?

For more information regarding how Hanna Instruments can help you with all of your testing needs, contact us, at sales@hannainst.com or 1-800-426-6287.

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Written by Amy King & 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. Amy graduated from The Pennsylvania State University with a Bachelor of Science in Food Science. Prior to her start at Hanna, Amy worked as a product developer for a global snack food company. She is passionate about all things surrounding food, especially its manufacturing and safety. Amy currently serves Hanna as the Food & Beverage Business Development Representative.