Food Protection Trends - March/April 2025 - 93

bohydrate source and concentration, contamination events
with spoilage microorganisms, microflora composition of the
inoculum, tea type, fermentation duration, and fermentation
conditions. These factors each have the potential to not only
influence health outcomes from consuming the beverage but
also the final brew in terms of food safety (10). Ultimately,
though popular interest in the potential health benefits from
consuming the beverage is increasing, literature substantiating
such benefits remains limited in scope and rigor, as
comprehensively described in a recent systematic review by
Kapp & Sumner (30). Nonetheless, consumers have taken a
keen interest in kombucha, thus spurring increased commercial
production of the beverage (31) and increased consumer
interest in making it at home.
Kombucha is made through the fermentation of
sweetened tea by a consortium of microorganisms, the
Symbiotic Culture of Bacteria and Yeasts (SCOBY), which
is scaffolded by a biopolymeric matrix of cellulose to
form a biofilm atop the liquid surface of the tea (55). The
flavor and safety profiles of the beverage rely primarily on
the metabolites of lactic acid bacteria (LAB), acetic acid
bacteria (AAB), and yeasts in the SCOBY that are generated
over the brewing process, including numerous organic
acids (56, 60). Of these, acetic acid is the predominant
organic acid in kombucha tea and is understood to greatly
contribute to its inhospitable nature toward pathogen
survival (20, 40, 55) by encouraging a typical pH of 2.5
or greater, but less than 4.2, which is understood to be
the critical limit for discouraging growth of bacterial
pathogens (41). Kombucha also contains components
with demonstrated antimicrobial activity, including
polyphenols, lactic acid, and indigenous bacteria, that
further impede pathogen survival (5, 8, 9, 11, 29, 38, 42,
51, 53, 54, 58). These components have been recognized
for their contribution to the antimicrobial characteristics of
kombucha, but the exact mechanisms and pathways remain
a subject of debate.
When properly brewed and stored, the beverage is relatively
inhospitable to pathogen and mold growth and may
even have the capacity to degrade mycotoxins (7). However,
when appropriate hygiene and sanitation measures are not
taken and/or when key elements of the fermentation, such
as pH, are brought outside of generally safe bounds by the
consumer, conditions may become welcoming to growth of
molds and pathogens introduced through contamination,
raising plausible food safety concerns for home brewers not
following recipes that have been validated for safety.
To the authors' knowledge, there has not been a confirmed
outbreak of illness caused by a foodborne pathogen
related to kombucha consumption to date in the United
States (U.S.). However, there have been case reports of
patients experiencing pathophysiological states, including
lead poisoning and lactic acidosis, wherein inappropriate
kombucha consumption or preparation approaches, and/or
93
Food Protection Trends March/April
unconfirmed contamination with foodborne pathogens had a
suspected role in the respective etiologies (10, 12, 19, 22, 40,
45, 49, 52, 59).
Multiple incidences of lead poisoning in individuals consuming
kombucha brewed and/or stored in ceramic containers
have been reported (9, 11, 42), wherein the acidity of
the beverage leached the mineral from the pot (40, 45, 59)
to the point that consumers were exposed to harmful levels.
Considering these aforementioned cases, it is evident that
consumer guidance regarding kombucha handling and preparation
can be made more robust and can be more effectively
communicated to consumers by researchers in order to better
safeguard public health.
The increased demand for validated home food preservation
recipes, coupled with the scarcity of available data, highlights
the importance of two critical steps: validating recipes to
ensure safety of the end-product and effectively communicating
these validated recipes to consumers. This is essential
not only for preventing foodborne illness but also for mitigating
other adverse health consequences that may arise from
potentially unsafe home fermentation practices. The research
study described herein aimed to establish safety parameters
for home-based kombucha brewing. These parameters were
determined with a focus on surrogate organism survival, which
was assessed in relation to sugar concentration and fermentation
duration. Furthermore, this study sought to elucidate the
pertinent factors influencing these safety thresholds, such as
acidity level, pH, and alcohol content.
MATERIALS AND METHODS
In collaboration with researchers and students enrolled in
food microbiology at the University of Georgia (UGA) and
Kansas State University (KSU), a challenge study integrating
Cooperative Extension and food microbiology teaching lab
settings was supported by the National Center for Home
Food Preservation (NCHFP) in the fall semester of 2022.
Surrogate strains: Surrogate organisms appropriate for
handling at Biosafety Level 1 (BSL-1) were utilized in
this study to minimize hazard exposure to the students
conducting the research. Selected surrogates were intended
to represent the survival behavior of the most probable
foodborne pathogens of concern in kombucha products,
such as those demonstrated to survive in acidic food milieu
and at refrigeration temperatures (10). The strains utilized in
this challenge study included Escherichia coli K12 (Migula)
Castellani and Chalmers ATCC 25404 (E. coli), an avirulent
Salmonella enterica subspecies enterica Typhimurium strain
LT2, H2S+ (Salmonella) (strain provided by Dr. Teresa
Bergholz from Michigan State University, Department
of Food Science and Human Nutrition), and Listeria
innocua Seeliger ATCC 33090 (Listeria), which served to
represent the survival of E. coli O157:H7, Salmonella enterica
subspecies enterica serovars, and Listeria monocytogenes
respectively (23, 43).
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