When it comes to fermentation, pH and food safety go hand in hand, and kombucha, of course, is no exception! Monitoring the pH during fermentation also provides valuable insight into its progress. This article will give an overview of pH and its role in kombucha brewing. We’ll cover how it’s measured and the practical benefits of monitoring pH during fermentation. We’ll also discuss how to use pH readings to track the fermentation process and troubleshoot any issues that may arise. By the end of this article, you’ll firmly understand pH and its importance in kombucha brewing, as well as the tools and techniques to measure and maintain a healthy pH in your brews.
Before we cover pH levels in kombucha, let’s review the basics. pH is a measure of the acidity or alkalinity of a solution, and plays a vital role in various chemical and biological processes. The pH scale ranges from 0 to 14, with 7 being neutral, defined as neither acidic nor alkaline. A pH below 7 indicates an acidic solution, while a pH above 7 indicates an alkaline solution. While pure water has a pH of 7, the pH of tap and well water can vary due to impurities and minerals. At the two extremes of the pH scale, we find battery acid, with a highly acidic pH of 0, and drain cleaner, with a highly alkaline pH of 14.
Now, let’s turn our attention to the chart below, which lists the general pH values of some everyday items. As you can see, lemon juice is also quite acidic, with a pH between 2 and 3. On the other end of the pH spectrum, bleach is highly alkaline, with a pH of around 13. Knowing the pH of an item can help in many applications, and when it comes to kombucha making, adjusting the pH is one of them.
Adjusting the pH means intentionally changing the pH of a solution to a desired level. This is commonly done in various industries to ensure the pH is within the acceptable range for the intended use.
For example, pH adjustments are crucial in winemaking to balance acidity and prevent spoilage. The optimal pH range for finished red wine is 3.4-3.5 pH; if it falls outside this range, the winemaker may correct the pH by adding potassium bicarbonate or calcium carbonate to raise the pH or tartaric acid to lower it.
When it comes to adjusting the pH value of a liquid, the process is straightforward. All you need to do is introduce a substance that is either more acidic or more alkaline, and it will shift the pH value in the desired direction. For instance, if you begin with pure water and add lemon juice, you’ll quickly observe a change in the pH reading. The water’s pH will no longer remain neutral at 7 pH; instead, it will fall somewhere between 2 and 7, depending on the amount of lemon juice you add. As the amount of lemon juice increases, the acidity of the liquid increases, and the pH value decreases accordingly. So, the lower the pH number, the higher the acid content. This simple adjustment method allows you to fine-tune the pH levels of liquids to suit your needs, whether for culinary purposes or other applications.
Now that we better understand pH and the adjustment process, let’s bring it all together and explore how it relates to kombucha brewing.
In kombucha brewing, the pH of the liquid changes throughout the process. To simplify this, I’ve broken it down into four distinct stages: the pH of the sweet tea before adding the SCOBY, the pH at the start of fermentation after adding the SCOBY, the pH during fermentation, and the pH of the finished kombucha. Let’s go over each.
The pH of Kombucha Through All Stages
Making kombucha always starts with brewing sweet tea. Before adding the SCOBY, the sweet tea’s pH will generally fall between 5 and 6.5, which is not acidic enough to discourage the growth of harmful bacteria during fermentation. Luckily, we now know how to adjust the pH, making it sufficiently acidic for kombucha fermentation. By lowering the pH to 4.5 or below, we can inhibit the growth of harmful bacteria, ensure the safety of the kombucha, and create the perfect environment for fermentation. So, how do we adjust the pH in this situation? Well, we do this by adding acidic, mature kombucha starter tea.
The next step in brewing kombucha is to add your kombucha culture, which consists of a pellicle (SCOBY) and liquid mature starter tea. Of these two, the starter tea is responsible for lowering the pH. Kombucha starter tea is acidic, with a pH value typically 3.5 or less, depending on how long the kombucha has matured. This level of acidity quickly lowers the pH when added to the sweet tea. Typically, a ratio of 12 fluid ounces of starter tea per gallon of sweet tea results in a new pH value between 3.8 and 4.4, depending on the strength and acidity of the starter tea. It is important to verify the pH using a pH test to ensure it is at or below 4.5, the threshold for inhibiting unwanted bacteria growth.
Once you add your kombucha culture to the sweet tea, fermentation is officially underway. During this process, the yeast consumes sugar to produce alcohol, and then the different bacteria consume the alcohol and create various beneficial acids like acetic and gluconic acid. As fermentation progresses, more sugars are converted to acids, so the sugar content decreases and the acidity increases. This shift gradually lowers the pH value. For example, if your kombucha batch starts at a pH of 4.