Fact or Fiction – Contamination in Non-Alcoholic and Low-Alcohol Beers

Time for another entry in my Fact or Fiction Series. There is an increasing interest in non-alcoholic and low-alcohol beers. This is driven by legitimate health concerns surrounding alcohol consumption, but in trying to address one health concern we may be exposing ourselves to another.

Non-alcoholic beers are made in a variety of ways. In some cases, a regular beer is brewed and the alcohol removed by distillation or reverse osmosis. In other cases, specialized approaches are used to generate a minimally-fermentable wort that is then fermented to less than 0.5% ABV. In either case you end up with a beer that is essentially free of alcohol. But there remains carbohydrates and proteins in the beer that is potential “fuel” for contaminating bacteria. At the same time, the absence of alcohol removes the protection alcohol provides from infection. So on the surface, it would seem that non-alcoholic beers may have a risk of infection.

Low-alcohol beers are just that: beers brewed with a low starting gravity that results in <3.5% alcohol by volume. That low level of alcohol has less of a preservative effect than does higher alcohol levels, potentially increasing the risk of contamination.

But how big are those risks?

A Brief Reminder – The Preservative Effect of Fermentation

Conventional beer fermentation produces a product that is somewhat resistant to contamination by a range of bacteria that can cause foodborne illnesses. In essence, there are four factors that work together to preserve fermented beer:

1. pH. As beer ferments, the succinic and other acids made by yeast drop the pH to between 4.0 and 4.5. While not highly acidic, this is acidic enough to slow the growth of many bacteria and to prevent the growth of spores from the bacterium which causes botulism.
2. Alcohol. Beer fermentation obviously produces alcohol, and while yeast are fine with alcohol concentrations upto 18% (or higher in some cases), most other microorganisms are not. Alcohol disrupts the membranes of cells, and at sufficient concentration can kill through membrane disruption and dehydration.
3. Hops. The alpha acids from hops are toxic to some Gram positive bacteria. While there are not too many foodborne illnesses caused by Gram positives, this effect does prevent souring by lactobacilli.
4. Nutrient deprivation. Yeast consume a lot of the sugars and proteins/amino acids present in wort during fermentation. So long as the yeast are then removed, these nutrients are no longer available to any contaminating bacteria. Unfortunately, beer yeasts do leave dextrins and some protein behind – which can be used by bacteria for growth. So the low-nutrient environment isn’t enough to control bacterial growth, but it does make the other three factors more potent.

Infection risk in Non-Alcoholic and Low-Alcohol Beer

Non-alcoholic beer would seem to be the most risky, due to the total absence of alcohol and the preservative effect it provides. Indeed, my one and only purchase of a modern non-alcoholic beer was clearly infected, and which a quick check under my microscope revealing the presence of a large number of bacteria. I’ve not bought one since.

Anecdotes aside, is the risk real?

Several studies indicate that yes, there is a risk.

In one study, a range of non-alcoholic and low-alcohol beers were tested, with these beers found to contain fairly high levels of carbohydrates that could be consumed by bacteria (between 45 g/L and 100 g/L, equivalent to specific gravities of 1.020 to 1.035), while conventional lagers had nearly none. The pH of these beers was within the normal range for beer. These beers were challenged with organisms recovered from draft beer lines, with the non-alcoholic beers developing significant contamination. The conventional lagers were fairly resistant to contamination, and the low-alcohol beers fell somewhere in the middle. Interestingly, adding alcohol to the non-alcoholic beers didn’t improve their resistance to contamination very much, even though the spiked beers now had inhibitory levels of alcohol and were at an inhibitory pH.

These results tell us a few things:

1. The low-nutritional environment of a fully fermented beer is a critical component of the beers resistance to infection.
2. Even high alcohol levels (8% ABV) and an inhibitory pH are insufficient to prevent contamination if a beer has significant residual nutritional content.
3. Low-alcohol beers are not as resistant to contamination than are high-alcohol beers, but are more resistant than are non-alcoholic beers.

But this study looked at contamination by organisms from beer lines, which (we hope) are unlikely to contain pathogens. So what about pathogens?

Here the news is even worse. In an older study non-alcoholic, low-alcohol, and “normal” beers were inoculated with four different pathogens that cause foodborne illnesses – Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus. The hops in these beers rapidly killed the Gram positive pathogens (S. typhimurium & S. aureus). However, the Gram negative pathogens were able to readily grow in the non-alcoholic beer. The low-alcohol beer allowed E. coli to survive, but not grow, while the regular alcohol beer killed everything. In a more recent study these results were replicated, finding that Gram negative bacteria grew quite well in non-alcoholic beers, even those with a pH as low as 4.2.

The Big Picture

What this means is that low alcohol and conventional beers are generally safe to produce and consume – their combination of pH, alcohol, hops, and low nutritional availability, protects them from many contaminants. Even in low-alcohol beers, these are sufficient to limit the extent to which a contaminant can grow.

On the other hand, non-alcohol beers are essentially growth medium for Gram negative bacteria. Their abundant carbohydrates support the growth of these organisms, despite their “inhibitory” pH and the presence of hops. Extreme care to ensure that the product is free of any contaminants and sterile bottling lines are needed to safely package these beers.

What Does This Means for the Craft and Home Brewer?

For myself, these results reiterate that I will continue to not purchase non-alcoholic beers. To package these in a way that limits the risk of infection requires both different processing than conventional beer (pasteurization, filtration, or preservatives) and a degree of cleanliness of the packaging line that most craft breweries cannot achieve. The equipment needed to keep these beers clean – especially during packaging – is expensive, and will probably remain in the realm of megabrewers (and highly specialized dedicated NA-brewers) for a while to come. Your conventional craft brewery who has one NA beer on tap probably isn’t set up to package a non-alcoholic beer safely. I’d note that the brewers association has reiterated much the same in their advice to brewers looking to make non-alcoholic beers (PDF).

Craft breweries have a very long history of producing quality low-alcohol styles such as bitter, mild, and Berliner Weiße. While these beers are more susceptible to contamination than are higher-alcohol styles, conventional brewery approaches to sanitation and packaging are more than sufficient to ensure the safety of these products.

As for brewing at home, I think this goes to show that while low-alcohol beer is no more risky to prepare than a more conventional beer, that non-alcoholic beers are probably out of our reach for a while to come. Achieving the level of microbial control needed to safely produce a contaminant-free non-alcoholic beer is beyond what is commonly achievable at home.

I’d like to thank Ruth, Dan, and Keith from over at Milk The Funk who brought up some of these papers and the idea for this post.