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Kombucha, a fermented tea beverage, is loved not only for its unique flavor but also for its probiotic properties, which can enhance digestive health. Its popularity has led many enthusiasts to brew it at home, allowing for personalized recipes. However, improper brewing techniques can pose significant food safety hazards.
Often referred to as mushroom tea, kombucha is a carbonated drink created from brewed black tea, sugar, and a SCOBY (Symbiotic Culture Of Bacteria and Yeast). The SCOBY consists of a diverse mix of bacteria and yeasts—some identifiable, others not—and can be purchased or shared by fellow kombucha brewers.
While recipes differ, the core brewing process involves fermenting a mixture of tea, sugar, and SCOBY for several days or weeks. This creates an ideal environment for microorganisms to flourish. Factors like fermentation duration, equipment quality, and other variables can make the process risky, leading experts to caution against homebrewing kombucha.
Illness Risks Are Present but Often Overstated
A quick microbiology lesson: Many microorganisms, whether harmful or beneficial, thrive in environments with moisture, nutrients (like sugar, fats, and proteins), temperatures between 40 and 140 degrees Fahrenheit, and pH levels ranging from 4.5 to 10. Unfortunately, kombucha fermentation meets all these conditions, making contamination more likely than you might expect. The paradox is that the same environment that fosters harmful pathogens is also essential for the beneficial bacteria and yeast to transform the mixture into kombucha. On the bright side, as kombucha ferments correctly, its acidity increases, creating a hostile environment for many harmful microorganisms.
Despite this, there have been documented cases of severe health issues linked to kombucha. A notable 1995 report by the Centers for Disease Control and Prevention (CDC) connected kombucha consumption to two illnesses in Iowa. One of the affected individuals died, but a follow-up investigation by the CDC and the U.S. Food and Drug Administration found no definitive proof that kombucha was the direct cause. No contamination was detected.
The CDC did discover that the surviving individual had fermented their kombucha for 30 days, far longer than the usual week, resulting in excessive acidity. Both individuals also had a pre-existing condition that impaired their ability to regulate their body's pH. Based on these findings, the CDC concluded that consuming 4 ounces of kombucha daily is safe for healthy individuals and advised against over-fermenting (typically 7-10 days) for homebrewers. Since the 1995 report, additional cases have associated regular kombucha consumption with lead poisoning, liver damage, cutaneous anthrax, and metabolic acidosis.
While there is a slight risk associated with brewing your own kombucha, it’s comparable to handling raw meat or canning foods, where unsanitary practices or negligence can lead to contamination by harmful pathogens. The key is to avoid carelessness.
Tips for Safely Brewing Kombucha at Home
Food safety starts with maintaining a clean environment. Most issues can be avoided by using sterilized equipment, working in a spotless area, and sourcing a healthy SCOBY from a reputable supplier. If you’re using a SCOBY from a friend, ensure they are experienced and verify the SCOBY’s quality by checking for black spots, mold, or other signs of contamination.
To preserve the beneficial microorganisms in kombucha, avoid using bleach or antibacterial soaps. Instead, clean all equipment and containers by submerging them in water heated above 160 degrees for at least 30 seconds. And, of course, wash your hands thoroughly. Beyond following instructions, keep these additional tips in mind:
Steep Tea in Boiling Water: Ensure the water temperature exceeds 165 degrees Fahrenheit when brewing your tea.
Opt for Glass Containers: The CDC advises against using ceramic or lead-based vessels for preparing or storing kombucha, as the tea’s acidity can leach harmful chemicals into the drink.
Use Adequate Sugar: White sugar fuels the bacteria in your SCOBY, and the right amount helps lower the pH level, reducing the risk of unwanted bacterial growth during fermentation. While some have success with honey, agave, maple syrup, and other sweeteners, options like molasses may fail to produce enough acetic acid bacteria, leading to subpar results.
Avoid Over-Fermentation: The standard fermentation period is 7-10 days, though some extend it to 30 days. Longer fermentation increases acidity and reduces sweetness, which may not suit those sensitive to highly acidic foods. Additionally, while alcohol content is usually below 1%, it can rise to 3% with extended fermentation.
According to a report from the Journal of Environmental Health, the highest risk of contamination during kombucha preparation occurs during fermentation. To reduce this risk, store your kombucha in a warm, well-ventilated area (around 70 degrees) away from direct sunlight, such as on top of your refrigerator or kitchen counter, and keep it separate from other items like plants to prevent cross-contamination. After seven days, ensure the pH level is below 4.2 by using pH testing strips like these.
If the kombucha doesn’t meet these standards, it’s likely contaminated or not fermenting properly due to insufficient warmth. In such cases, discard the batch and start anew rather than attempting to salvage it.
Initially, you might misinterpret brown stringy bits, white spots on the surface, or the formation of a “baby SCOBY” as signs of contamination, but these are normal. Regularly inspect your SCOBY for mold or unwanted bacterial growth. Mold, similar to what ruins bread, often appears as green or black floating particles on the kombucha’s surface. Check out this example of moldy kombucha. If in doubt, discard the batch and begin again—it’s not worth the health risk.
Test your kombucha’s pH using testing strips, which should show a reading between 2.6 and 4.2. Alternatively, you can taste a small amount using a straw. The kombucha should have a vinegary taste and smell, not a cheesy or rotten odor.
While there’s limited scientific backing for the extravagant health benefits often claimed by kombucha enthusiasts, the beverage remains a flavorful and simple homemade option. However, brewing it at home requires caution, as mistakes can lead to unpleasant outcomes. At best, it might taste like sweaty gym socks; at worst, it could pose serious health risks.
Illustration by Angelica Alzona. Images by cheeseslave and Sterling College.
