Microbial Safety of Cold Brewed Black Coffee during Retail
Shirin j. Abd, Martha Kimber, Daljit Kaur, Fei Wang, Anne Nillo, and Wilfredo Ocasio
Eurofins Microbiology Laboratories, Inc. Fresno, CA
ABSTRACT
Introduction
Cold brewed black coffee products are brewed with cool or ambient temperature water, often without any thermal processing steps, and generally have pH and water activity values which may allow for the growth of pathogenic microorganisms. Therefore, the microbiological safety at point of-sale for these products requires consideration of factors like storage time, temperature, and inherent antimicrobial properties on the potential for pathogen growth.
Purpose
To evaluate the microbiological safety of 1) immersion method concentrated coffee, and 2) single strength cold brew coffee processed by UHT. The results were used to determine if temperature controls for safety (TCS) should be required for these products during retail.
Methods
Separate multi-strain cocktails of Bacillus cereus, proteolytic Clostridium botulinum, non-proteolytic C. botulinum, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Staphylococcus aureus were inoculated into cold brew coffee concentrate (pH 5.28-5.39, 3.5-4.5% Brix) or single strength cold brew (pH 4.85-5.04, 1.6-2.0% Brix) at a target level of 2-3 log CFU/ml and then stored at 29°C for 11 days. For each product, storage condition, and sampling time, 3-5 replicate samples were enumerated by plating. Additionally, C. botulinum samples were evaluated for the presence of botulinal toxin using the DIG-ELISA method. Two independent trials were performed.
Results
For both coffee products, population levels of E. coli O157:H7, Salmonella, and S. aureus declined below the detection limit in ≤3 days. Population levels of L. monocytogenes declined more slowly under anaerobic storage conditions as compared to aerobic storage conditions (p<0.05). Growth of B. cereus and C. botulinum was not observed over the storage period, and botulinum toxin was not detected.
Significance
The results of the challenge studies demonstrate that the cold brew black coffee products do not support growth and/or toxin production of pertinent pathogens identified for this product category. Therefore, temperature controls for safety (TCS) are not required for these cold brewed coffee products.
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