Quantifying the Destruction of Salmonella spp. during a 24-hour Kombucha Brewing Process

Introduction:  Kombucha is a fermented tea that has been consumed for hundreds of years; however, recently kombucha’s popularity has risen as consumers shift to more health-conscious beverage options. The Symbiotic Culture of Bacteria and Yeast (SCOBY) operates as a fermentation mechanism to transform sugar in the sweet tea mixture into a carbonated, tangy, acidic beverage that is the hallmark of kombucha. With the rise of home-brews, it is important to investigate safety of the kombucha-brewing process.

Purpose:  This study examined the reduction of Salmonella spp. during the traditional kombucha home-brewing process.

Methods:  Kombucha was prepared using a locally purchased SCOBY and the traditional method, which includes brewing green tea in boiling water, followed by the addition of sugar and SCOBY. Kombucha and SCOBY-free sweet green tea (control) were inoculated with a Salmonella cocktail (Salmonella Montevideo, Salmonella Typhimurim, Salmonella Anatum, and Salmonella Newport) at a target concentration of 4 log CFU/ml and stored at 24.4°C. At 0, 1 3, 8, and 24 hours, pH of each sample was monitored and Salmonella populations were enumerated on Xylose Lysine Tergitol-4 agar.

Results:  There were significant effects of treatment (P<0.0001) and treatment*time (P<0.0001), with kombucha harboring significantly reduced Salmonella populations compared to the control (P=0.0142) by three hours. Upon reaching 24 h, kombucha harbored 6.7 log CFU/ml (P<0.0001) less Salmonella than did the control. Throughout the 24 hour time period, the pH of kombucha and the control was approximately 3 and 7, respectively.

Significance:  The kombucha home-brewing process used in this study was effective at reducing Salmonella populations to 0.55 log CFU/ml. These data suggest that Salmonella contamination of the raw ingredients used in kombucha may be controlled by traditional kombucha brewing practices; however, because brewing practices and the microbiological quality of each SCOBY can vary, additional research is necessary to determine safety.