Kombucha Defense Mechanisms
Kombucha is a living symbiosis of bacteria and yeast that has been brewed in homes and shared with others for hundreds if not thousands of years. A living culture with such a long history must have some way of protecting itself from causing harm to those who care for it (i.e. homebrewers) or surely it would have been ditched generations ago.
While our ancestors simply had to trust their gut, modern science is discovering the important role fermented foods have played in our culinary culture since recorded history (if not longer). The Human Microbiome Project has just begun to illuminate our understanding of the relationship between gut bacteria and health, but some of the preliminary findings are confirming what our ancestors instinctually knew: As Bacteriosapiens, fermented foods provide us with the regular influx of healthy, living bacteria our bodies need in order to boost proper functioning. The Kombucha culture evolved a few different defense mechanisms to protect itself from invasion from harmful microorganisms – low pH, ethanol and the SCOBY itself are all means that ensure the longevity of the culture. Let’s take a look at pH and the role it plays in protecting the culture.
pH & Kombucha
As you recall from the Top 5 Signs of Healthy Kombucha Brew, pH plays an important role in protecting the SCOBY from microbial invaders. Kind of like a chemical force field, the low pH creates a highly acidic environment in which our native bacteria and yeast thrive but simultaneously inhibits the growth of disruptive foreign & potentially harmful microorganisms.
pH was first conceived by Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909. Carlsberg Lab was set up by the Danish beer brewing company to advance biochemical knowledge, especially as applied to brewing beer. While studying proteins, Sørensen devised the pH scale as a means to express the concentration of hydrogen ions present in a solution.
While there are conflicting explanations for the definition, the most commonly accepted answer is that “p = potential” and the “H = hydrogen.” pH is a measurement of the acidity or alkalinity of a solution. When a substance dissolves in water, it produces charged molecules known as ions. Acidic water contains extra hydrogen ions (H+) and basic (alkaline) water contains extra hydroxyl (OH-) ions. As we can see on the chart below, the relationship from one pH level to the next is exponential.
The pH scale ranges from 0-14 with readings in the 0-7 range termed acid and readings in the 7-14 range termed alkaline. 7 is considered neutral and the ideal pH for our blood is just above 7. Without going into too many details, there is an important correlation between pH and health. While Kombucha tests on the acid side, much like lemon juice or apple cider vinegar, when it hits the digestive system it creates an alkaline ash. (See pH post part 2 which will also include how to track your own pH).
Image courtesy http://staff.jccc.net/pdecell/chemistry/phscale.html
The symbiosis of Kombucha cultures occurs between the yeast and bacteria, organisms which have evolved to work together via a system of balanced competition, with each contributing to the health and life cycle of the other. Acetobacter/Gluconacetobacter, the dominant type of bacteria in Kombucha, creates acetic acid - one of the most healthy acids and a clue to Kombucha’s low pH.
Most have heard of the health benefits of acetic acid in the form of consuming small amounts of vinegar, which is typically a 4-7% acetic acid solution, whereas Kombucha checks in at a much more palatable ~1% acetic acid, often much lower in commercial versions.
On the pH scale, white distilled vinegar tests around 2.4 pH while a properly brewed batch of Kombucha may fall anywhere from 2.5 – 3.5. With this knowledge we can then infer (and taste!) that the lower the pH, the tarter the Kombucha. Obviously then, the obverse is also true – the higher the pH, the sweeter the Kombucha.
However, pH does NOT indicate that the Kombucha has finished the fermentation process. It confirms that the brew is protected from microorganisms. The pH should drop to the correct range of 3.5 and lower within the first few days of brewing. We use our most sensitive tool – our tongues – to decide when the appropriate amount of sugar has been converted.
So while liquids with high concentrations of acetic acid have a low pH, they are correlated but not directly related. For example, apple cider vinegar (5% acetic acid) from my pantry tests as 2.9 pH while my flavored homebrew Kombucha (~1% acetic acid) comes in at 2.7 pH. Yet the ACV is undrinkably sour and disgusting while my Pink Lemonade Kombucha (or even unflavored booch which checks in at 2.5 pH) is dry, tart and delicious. Admittedly, we like our Kombucha sour. By tasting and testing, one can train the palate to discern the subtle differences in flavor and match them to the pH value, especially when tracked along with brewing time.
According to the FDA’s guidelines for compliance, foods with a pH of 4.6 and lower have been deemed safe for sale without needing further preservatives: “When the pH of a food is 4.6 or below, spores of C. botulinum will not germinate and grow.” This means that not only is your KT safe from invasion by harmful microbes, but so are you!
The Ideal pH for Kombucha is 3.5 – 2.5
Researchers in Brazil found that Kombucha’s antimicrobial activities protected against E. coli, Salmonella typhi & M. canis and were found to be most effective after 28 days of fermentation (perfect for Continuous Brewers!). Their research also revealed the cyclical nature of the symbiosis. After about 14 days of steadily declining pH, the activity shifted and the pH gradually rose and peaked again at 21 days, then shifted lower again at 28 days (see graph below). These peaks and valleys indicate the ebb and flow of the symbiotic process of Kombucha.
First the yeast consume the sugar and produce CO2 & ethanol, then the bacteria consume the ethanol and produce healthy acids. The process repeats itself as the bacteria and yeast feed upon each other’s waste products. Adding sugar in the bottling stage reactivates this process and yields a different flavor than a freshly decanted Kombucha tea. Priming sugar is either a pinch of sugar added to the bottle or comes from the fruit or other flavoring agents. When added in the secondary stage, in an air tight environment, it reactivates the yeast which releases CO2 into the liquid. This is how we boost the natural carbonation that so many Kombucha drinkers love.
This low pH environment also means that Kombucha seldom “goes bad” in the way that we normally think of food spoilage. As Sandor Katz has said, fermentation is one of nature’s methods of preservation. The low pH prevents organisms responsible for spoilage from surviving. The ferment remains active in both an anaerobic environment (without oxygen, i.e. in the bottle) and at colder temps (i.e. in the fridge), just at a much slower pace.
Good Sanitary Practices are Key!
As with all food preparation, it is important that sanitary practices are observed in order to prevent illness. Here are some tips for safely brewing Kombucha at home.
How to Test Your Kombucha pH
The easiest way to test the pH of your Kombucha is with pH strips or with a pH meter. If using pH strips, be sure they are in the correct range for your Kombucha (0-6). The strips are an easy, disposable way to check that the brew has reached the correct level of acidification. The meter offers greater precision and uses.
- Dip the pH strip in the Kombucha tea.
- Immediately compare with the color coded guide.
- The closest color match indicates the pH level.
- Calibrate the pH meter with the included buffer solution packet. Use the included screwdriver to manually adjust the setting to 7.0
- Rinse off buffer solution with filtered water.
- Place the pH meter in a small dish of Kombucha.
- It may take 10-30 seconds for the meter to settle on the correct reading.
- Use a small piece of damp sponge at the bottom of the black cap to keep the electrode moist.
Tasting your Kombucha and testing the pH will help you recognize the different stages of the brewing cycle. Once they are familiar, you will easily be able to detect where you are at in the process with just a sip or two!
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