Tuesday 18 February 2014

Fact or Fiction? Can Pathogens Survive in Beer?

My blogging has been not overly great in 2014 - between illness, an unseasonably cold winter and an unusually busy work schedule I've not been able to brew much this year. But motivated by this thread at HBT I thought a brewing science-based post may be in order.

This post covers a popular pseudo-myth, that no human pathogen can survive in beer. Much of this is based on the history of beer brewing, where the brewing process was used (not knowingly) to sanitize otherwise contaminated water, and then to add various things (acidity, hop compounds, alcohol) that would then act as a mild preservative. This has since been extrapolated to the assumption that no pathogen can survive in beer.

As it turns out this is neither a simple question, nor does it have a simple answer. For those who want the Coles notes version, yes, pathogens can survive in beer. But the chances of them causing you harm are negligible. The other bad health effects of ethanol are a far higher risk than is the minimal risk of infection.

For the longer answer, look below the fold...

What is a pathogen?
While the answer to this question seems obvious to most - a microorganism that causes disease - its not so cut & dried.  Some organisms are hard-core pathogens, taking pathogenicity to the point that they solely survive by infecting people. Still others live the bulk of their lives in the environment, but easily infect people if they have the opportunity.

But many others are more complex - there is a whole host of organisms that happily live in/on our bodies, in total harmony with us, and only cause infections when conditions permit - e.g. gaining entry via a wound, or following suppression of the host's immune system. Still others live happily in the environment and only cause infections in the rare person who is susceptible - often due to an immunodeficiency or immunosuppression.  These latter two groups of pathogens are referred to as "opportunistic pathogens", and when talking about pathogens in beer represent the most common "threat".

What do we mean by "beer"?
Again, a seemingly obvious answer, but in the homebrew world its not as simple as in the beer store. Do you only mean fermented wort, or is unfermented wort included as well? While fermented wort is a hostile environment - acidic, nutrient deprived, bactericidal hop compounds and containing not insignificant amounts of ethanol - unfermented wort is a very friendly environment for some pathogens. Of particular concern to the homebrewer is pathogens that can grow in the unfermented wort, and survive once yeast take over and complete fermentation.

What makes beer antibacterial?
Ignoring its chemistry, the main antibacterial aspect of beer is its preparation - long boils kill pretty much any pathogen, leaving behind only a few viable spores. These spores typically do not survive fermentation, meaning that brewing a beer can clean up nearly any water source.

Chemically, beer is not antibacterial due to any one compound, but rather due to a combination of things.  Alcohol, for example, can inhibit a number of pathogens, but other pathogens do just fine in the presence of alcohol. As an extreme example, the pathogen Mycobacterium nonchromogenicum can survive over 75% ethanol. So while ethanol kills some pathogens, others are pretty much oblivious to its presence. Sadly, with the broad availability (and massive mis-use) of alcohol-based hand sanitizers, ethanol-resistant pathogens are becoming ever more prevalent.

Hop compounds also inhibit some bacteria - specifically, members of the gram positive group of bacteria. But this lethality is not universal among the gram-positives (e.g. hop-resistant lacto strains are still gram-positive), and of course these compounds don't do squat for gram-negative and other non-gram positive pathogens.

Finally, there is the acidity of the wort. Most beers finish below pH 4.5, which is the threshold for antibacterial acidity. But many pathogens have no issue with low pH's - indeed, any pathogen that enters via our guts must be able to survive several hours in our stomach, which has a pH around 2; or nearly 100X more acidic than your average beer.

Overall, none of these chemical characteristics are sufficient to keep beer pathogen-free - most pathogens will survive fine if exposed to just one of the above antibacterial compounds; but the combination of the three is lethal to most bacteria.

What has science shown?
The answer is - unsurprisingly - very little. My lab studies a few pathogens as part of its broader scope, and I can tell you that we've not once thought about looking at whether they'd survive in beer. Most brewing science is orientated at commercial brewing, and the simple reality is that the sanitation methods used by commercial brewers is more than adequate to ensure that pathogens do not make it into the beer.  In addition, illnesses caused by homebrewing would be nearly impossible to detect - its nearly impossible to track down infections that do not spread to a number of people; tracking down the source of a rare and intermittent infection is nearly impossible. As such, not much has been done to assess the risk. So what do we actually know?
  1. The putative pathogen Arcobacter, which is closely related to a few more serious human pathogens, appears to survive just fine in beer. In fact, it did fine in upto 10% alcohol.
  2. The food borne pathogens Escherichia coli O157:H7, Salmonella Typhimurium survive in beer. In addition, Escherichia coli (and perhaps the Salmonella) grow well in unfermented wort - indeed, the Escherichia coli are the "enteric bacteria" that grow in the initial stages of a wild ferment, such as those used to prepare lambics.  Study 1, 2.
  3. Many of the oxidative yeasts that appear early in wild ferments - Rhodotorula, many Candida species, even some strains of Pichia (which are closely related to Brettanomyces) can cause infection in immunosuppressed or immunodeficient patients.
  4. I've found Cryptococcus neoformans (a pathogenic fungus) in one of my attempts at harvesting wild yeasts. I've not seen any other references to this in beer, but it non-pathogenic species of Cryptococcus has been found in wild wines.
  5. Most importantly, I've been unable to find any confirmed cases of food-borne illness being passed by either homebrewing or commercial beers.
EDIT: as Dan noted in the comment section, a recent paper has further addressed this issue, looking at commercial beer and rive wine. Several pathogens were found to survive for intermediary-to-long-term in beer, the same ones as mentioned in point #2, above.

What does this mean?
The answer is simple - so long as your sanitation is good there is little to no risk - indeed, the other medical concerns related to alcohol consumption are far more likely to harm your health.

But there are a few caveats:

If brewing wild beers (lambics, etc): If doing wild brews you should take care to clean your fermenters and your hands, in order to minimize the risk of enteric bacteria gaining a foothold in your beer. Of the above-listed risks these are the greatest risk. In fact, some commercial lambic brewers in the EU have begun taking precautions to reduce enteric bacteria, out of a concern that on rare occasion people may have contracted food poisoning via these beers. As homebrewers, we should be considering taking similar precautions.

If you have an immunodeficiency or are immunosuppressed: Obviously, don't take medical advice off the internet.  Talk to your MD to see if you are at risk of infection - especially if you're condition/treatment increases your risk of fungal infections.  If so, or if you are concerned, stick to beers that are fermented using commercial strains of Saccharomyces yeast.


  1. This is very similar to all the people who don't mind leaving their meat out far too long on the counter to defrost, expecting the heat of cooking to kill everything. Sure, it will decimate the population of most anything alive, but I certainly wouldn't want to eat a piece of meat cooked well enough to actually sterilize it. And not to mention that some create heat resistant toxins which persist even after the death of the pathogen itself.

    As in all things in life, its best to use some common sense instead of relying on absolutes, rules of thumb, and old wives' tales.

    - Dennis, Life Fermented Blog

  2. Great post. I had previously come across some of that in the past but it's nice to have it stated clearly. It's clearly a negligible danger but being willfully ignorant isn't in anyone's favor. I would be interested in seeing what happens when contaminated yeast slurry, say one with O157:H7, is repitched repeatedly.

    I can add that I isolated what seemed to be Rhodotorula from the then-2 year old sample of DCambic I got DCY02 and 03 from. Granted, a year of that was in my fridge, but still. Of course I drank the finished product later without issue.

    Thanks also for reminding me why I don't participate on HBT. I loved the highly ironic bit about "regurgitation" from what "they" said.

  3. Bryan, I am curious if you are in agreement with Dr. Colby on the risk of Botulism in "No Chill" brewing?


    1. Geez, blogspot's eaten two replies...third time the charm?

      I agree with him, in that it is a theoretical risk. Boiling wort renders it anoxic, but would not kill botulism spores. Sealing the hot wort in a container would then keep it anoxic, allowing spores to germinate and grow once the wort cools sufficient.

      That said, other members of the Clostridium genus (the genus to which botulism belongs) are known to be hop-sensitive, and so the hops in the beer may be protective. Again, entirely theoretical as no one has tested hop resistance in Clostridium botulinum AFAIK.

      Personally, I wouldn't do it. While the risk of botulism is generally low, the severity and high mortality rate of the resulting disease is serious enough that I don't think the risk balances out the benefit.

    2. For No Chill storing of hot wort, what if you added Phosphoric acid to lower the wort pH to 5.0
      Would that be enough to stop Clostridium spores from germinating?
      If 5.0 isn't low enough that what about 4.5?

      Though I wonder if that would affect the beer this wort would produce.

      (I can't log in from work)

    3. You can control botulism by pH, but you need to be at a pH of 4.2 or lower (this is the standard used for canning and in the food preparation industry). However, at that pH you may be stressing the yeast and/or causing some changes in the yeast behaviour, as 4.2 is typically where beers finish (pH wise).

  4. I'm sure you have seen this, but another study to reference: http://www.ncbi.nlm.nih.gov/pubmed/24674433

    1. I had not seen that one, info now added to the post.



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