The affect of temperature and pH on the food safety of kombucha tea

Abstract

Objectives: Kombucha tea is becoming an increasingly popular food item within the Vancouver area. The tea is prepared through fermentation at room temperature during which acidic by-products are produced lowering the overall pH of the tea. Though the pH eventually reaches levels below 4.6, many health authorities prevent the sale of kombucha in farmers markets due to potential food safety issues. The initial pH before fermentation is around 5.5 and is then left at room temperature to ferment. As a result, this process potentially could allow for food borne illness causing organisms to survive and proliferate within the sugared tea. This research project will investigate the relationship of pH and time during fermentation at both room and refrigeration temperatures. Fermentation within a refrigerator could provide a safer alternative fermentation method Methods: The pH was measured using a pH meter for 30 samples at both room and refrigeration temperatures providing a total of 60 samples. The pH was measured periodically every twelve hours for a total of 120 hours. The data was analyzed using a linear regression model to determine if the pH change over time was statistically significant. The time at which the pH dropped below 4.6 was also noted for food safety purposes Results: At room temperature the pH steadily decreased in a linear fashion throughout the entire sampling period, dropping below 4.6 within 12 hours. The pH decreased in a nearly identical fashion when fermented in a refrigerator for the first 72 hours of sampling. After the 72 hour mark the pH stabilized at approximately 3.75, whereas the pH at room temperature continued to decrease down to 3.10 after the full sampling period Conclusion: The results indicate that kombucha tea becomes a non-potentially hazardous food within the first 12 hours of fermentation. The pH dropped below 4.6 after 12 hours at which point no food borne illness causing bacteria are able to survive and proliferate within the tea. The observed decrease in pH during the first 72 hours within a refrigerator is unlikely to have resulted from the fermentation process and therefore is not a feasible practice. Fermentation at room temperature appears to be a relatively safe process if home brewers are able to measure the pH change and carry out the process in a sanitary manner