Kombucha Brewing under the Food and Drug Administration Model Food Code: Risk Analysis and Processing Guidance

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Introduction

Kombucha is a fermented beverage made from brewed tea and sugar. The taste is slightly sweet and acidic and it may have residual carbon dioxide. Kombucha is consumed in many countries as a health beverage. It is believed to have prophylactic and therapeutic benefits toward a wide variety of ailments (Greenwalt, Steinkraus, & Ledford, 2000).

The kombucha process resembles a vinegar fermentation. Like vinegar, kombucha is a yeast fermentation of sugar to alcohol followed by a bacterial fermentation of alcohol to acetic acid. The symbiotic culture forms a pellicle or biofilm on the surface of the brew often called a mushroom or SCOBY (symbiotic culture of bacteria and yeast). The yeasts in the mixture metabolize sucrose into glucose and fructose, then into ethanol and carbon dioxide (Mayser, Fromme, Leitzmann, & Grander, 1995). Ethanol is then oxidized by the bacteria (in the presence of air) to acetaldehyde, then to acetic acid (Mayser et al., 1995). Typically, the alcohol and acetic acid content of kombucha is less than 1%, respectively, but each can rise to 3% during a long ferment (~30 days; Mayser et al., 1995). The acetic acid bacteria also utilize glucose to produce gluconic acid to approximately 2%. Fructose is used to a lesser extent and some remains after the fermentation. Some glucose will remain unmetabolized, and together with the remaining fructose, provides sweetness.

As a fermented beverage, kombucha would be categorized in the Food and Drug Administration (FDA) model Food Code as a specialized process. A retail or food service operator would need to request a variance from their regulatory authority as defined in the Food Code section 3-502.11 (Food and Drug Administration [FDA], 2009). This section also requires that the operator submit a food safety plan to the regulatory authority for approval before commencing operations. Below is a hazard analysis and critical control points (HACCP)-based risk analysis of the process to help both operators and regulators maintain safe production of kombucha.

Process Flow

Naturally, kombucha recipes will vary. The general process has been described by Greenwalt and co-authors (2000) and includes infusing tea leaves (~4-5 g/L) into freshly boiled water. Sugar (sucrose) is added at 50-150 g/L (5% to 15%). The tea is allowed to brew for approximately 10 minutes and the tea leaves are removed. The tea is cooled to room temperature and approximately 100 ml/L (10%) of fresh-fermented kombucha containing the microbial mat from a previous batch is added to the sweetened tea. It is then covered with a clean porous cloth (e.g., cheese cloth) and incubated at room temperature for about 7-10 days. If the fermentation is allowed to continue beyond 10 days, acidity may rise to levels potentially harmful to consumers (equivalent to drinking undiluted vinegar).

Kombucha Hazards Analysis (Table 1)

Biological Hazards

Most boiling water with black or green tea infusions start at a pH of [less than or equal to] 5. Once fermentation starts that pH is reduced in approximately seven days to a finishing pH of [less than or equal to] 2.5. Fermentations such as wort to beer have a similar pH reduction during fermentation, although beer will finish closer to pH 4. Since the initial infusion uses boiling water we consult Table A of section 1-201.10(B) (FDA, 2009) to determine if this is a potentially hazardous food (PHF). The tea infusion would not be a PHF if the pH were <4.6. Since the tea is heated but not packaged, however, it may be subject to contamination after cooling. Therefore, we must also consult Table B of section 1-201.10(B) (FDA, 2009) that requires a pH [less than or equal to] 4.2 to be a non-PHF Since kombucha starts at a potentially hazardous pH (~5) and finishes below 4.2 this process would require food safety monitoring to ensure safety. This is also confirmed in the Food Code under section 3-502. …