Non-alcoholic beers may be a happy hour for bacteria, study warns

In a recent study published in the Journal of Food Protection, researchers investigated the effects of antimicrobial variables, including storage temperatures, pH, and ethanol concentrations, on common bacterial populations in low- and non-alcoholic beer. They inoculated variable-controlled replicates of non-alcoholic beer with five bacterial strains and monitored bacterial populations over 63 days. Their findings suggest that low-alcoholic beers prevent pathogen growth, while non-alcoholic beers allow it.

Study: Survival of Foodborne Pathogens in Low and Non-Alcoholic Craft Beer. Image Credit: DALL·E 3

Alcohol is an ideal antiseptic

Conventional alcoholic beers have been considered immune to foodborne pathogens, given their intrinsic properties and processes that form an essential part of their manufacture. Their inherent antimicrobial properties include ethanol content, hops bitter acids, acidic pH, dissolved carbon dioxide, anaerobic conditions, and low sugar content. When combined with pasteurization, wort boiling, filtration, and refrigerated storage, cases of food poisoning from beer are rare.

Research has depicted that ethanol concentrations of 3.5% – 5% (vol) can effectively prevent the growth of most common food pathogens. While certain bacterial strains have been shown to survive even in full-strength beers, these are usually due to poor prolonged refrigeration.

In recent decades, and especially since the coronavirus disease (COVID-19) pandemic, there has been a shifting trend in consumer demand from alcoholic beer to low- (<2.5% alcohol by volume [ABV]) or non-alcoholic (<0.5% ABV) beer. This shift has been attributed to demographics, religion, social regulations, health, and consumers choosing to regulate their calorie intake.

Given their lower than 3.5% ABV, low- and non-alcoholic beers may be at risk of pathogenic growth if bacterial contamination is introduced at any step during the beverage’s production. Unfortunately, most research on the association between foodborne pathogens and beer is restricted to traditional beer, with a severe dearth of data on non-alcoholic beers.

About the study

The present study aims to investigate the impacts of ethanol concentration, storage temperature, and pH on the growth of five strains of Escherichia coli (E. coli), Salmonella enterica, and Listeria monocytigenes in low- to no alcohol-containing beers.

Non-alcoholic canned beer with baseline ethanol and pH concentrations of <0.5% and 3.65 were adjusted using O.1M sodium hydroxide (NaOH) and 99% ethanol. Final concentrations of pH 4.20, 4.50, and 4.80 and ethanol = <0.50% and 3.20% ABV in triplicate were prepared in sterile, parafilm-sealed vials. E. coli O157:H7, S. enterica, and L. monocytogenes were added to the vials, which were subsequently stored at four and 14°C for 63 days.

Periodic sampling to test for pathogen growth or die-off involved streaking beer samples on Violet Red Bile Agar (VRBA), Modified Oxford Media (OX), and Bismuth Sulfite Agar (BSA) to test for E. coli, L. monocytogenes, and S. enterica, respectively.

Statistical analyses comprised one-way analysis of variance (ANOVA) to evaluate the effects of storage temperature, ethanol content, and pH on pathogen populations.

Study findings

 E. coli and S. enterica were found to survive in low- and non-alcoholic beer at all temperatures, pH, and % ABV under study. L. monocytogenes was observed to be less resilient, with population size declining below the detection limit after a few days.

In non-alcoholic beer, pH was associated with declines in microbial population sizes across tested strains – at 4°C, pH 4.20 resulted in a 1.23 log-transformed decrease in E. coli population size, while pH 4.50 resulted in a 2.37 log reduction in S. enterica. L. monocytogenes was below the detection limit at all pH values, though lower pH was associated with more rapid population reduction. At 14°C storage conditions, E. coli and S. enterica populations were observed to grow regardless of pH. In contrast, for L. monocytogenes, higher storage temperature was found to result in more profound population declines compared to 4°C.

In low (3.20% ABV) alcohol-content beers, all microbes presented population declines at 4°C. At 14°C, E. coli and S. enterica depicted population declines but persisted at low population sizes throughout the study period. In contrast, L. monocytogenes population sizes rapidly reduced below the minimum detection limits by day 6 for pH 4.20 and 4.50 and day 10 for pH 4.80.

These findings suggest that % ABV and storage temperature are the most critical determinants of foodborne pathogen persistence and growth, trends confirmed by ANOVA analyses.

Conclusions

In the present study, researchers investigated the effects of % ABV, storage temperature, and pH on the growth and persistence of foodborne pathogens in low- and non-alcoholic beers. They inoculated pH (4.20, 4.50, and 4.80), temperature (4 and 14°C), and % ABV (<0.50 and 3.20) standardized beer with a five-strain cocktail of E. coli, S. enterica, and L. monocytogenes and monitored bacterial growth over 63 days.

Alcohol content and storage temperature were revealed to be the most significant determinants of bacterial growth, with non-alcoholic beer being far more susceptible to microbial growth than low-alcoholic beer.

“Due to the increased susceptibility to spoilage and pathogens, the formulation of those beverages must be evaluated for safety by a Process Authority. Low and non-alcoholic beers should be processed through pasteurization, to achieve commercial sterility. Sterile filtration and the addition of preservatives should be considered as additional steps to reduce this microbial risk.”