Anti-Microbial Effect of Ethanol In Beer - 5 Possible Reasons Strong Beers Age Well (Part 2)
By jason on Oct 24, 2007 in Cellaring Science, Featured
Before reading on, make sure to check out the introduction to this series on the aging of high-alcohol beers.
1. Microbial Growth Inhibition- High ethanol levels inhibit the growth of micro-organisms that cause beer spoilage.
If you read enough of the literature (what little there is) on beer aging, you’ll eventually come across somebody mentioning that the high ABV% of beers prevent the growth of nasty tasting bacteria in your beer. In the medical world, there can be no doubt that certain alcohols can be effective in eradicating microorganisms. But does this hold true with Ethanol, especially at the concentrations we typically see in beer?
With the advent of modern sanitation and bottling methods, incidents of beer contamination nowadays are very rare. However, years of cellaring can take their toll on the integrity of a bottle’s seal. Thus, it is definitely worthwhile to discuss the effects of high abv% on possible bacterial contaminents.
To shed some light on this issue, we can turn to a study done in 1995 and published in BMJ (British Medical Journal) entitled “Wine as a digestive aid…“. This study examined the effects of wine and other control liquids on bacteria growth. One of the control liquids they used was a mixture of water and ethanol at a level of 10%, which neatly simulates the abv% of many of the beers we cellar.
This study, while demonstrating the anti-microbial effects of wine, also showed that the 10% ethanol mixture had virtually no effect on the bacteria. Here’s a nice little graph illustrating the results:
The paper goes on to say that wine’s effects on bacteria seem to be associated with the various polyphenols in wine that are produced during fermentation. Beer is also known to to be packed with polyphenols, and it wouldn’t be hard to imagine that they could have a similar anti-bacterial effect.
These results can only lead us to the conclusion that if it is true that higher abv% beers resist spoilage better, the effect is almost certainly NOT directly due to the ethanol levels present.
Next time I’ll be discussing ethanol’s possible effect on masking undesirable flavors in beer.
Jason
It is a mistake to exprapolate the effects of 10% ethanol solution on human enteric pathogens on an agar plate (a very favorable bacterial environment) to how ethanol effects possible growth in a bottle of beer. Different pathogens, different culture mediums, different conditions.
Aaron Tom, MD
B.A. Chemistry
Home Brewer
Certified Beer Judge
Aaron Tom | Sep 14, 2008 | Reply
Looking at the charts, the last two seem to show that bacteria levels have started to drop after 24 hours in the 10% ethanol solution. So in terms of aging…well, doesn’t it seem that this would continue to work after 1 day…so that after a week or two the levels would be considerably lower?
Another thought is that this study is looking at the problem backwards - it looks at how well different drinks kill off bacterial colonies. But in aging beer, the challenge is to prevent them from growing in the first place. Again, an anaerobic, 10% ethanol solution seems to me to be a fairly inhospitable place.
iwouldntlivethere | Nov 12, 2008 | Reply