My last two batches have been infected with a bacteria infection. I'm curious what species of bacteria could survive the alcoholic conditions of the brew? The first infected batch appear to have colonies post-bottling, coating the inside of the PET bottles with what appear to have the size and spread of typical Lactobacillus colonies. My second infected batch had a large colony in the area of the Krausen Collar in primary fermentation - seemed to be more shiny and gooey reminiscent of an aerobic bacteria of some sort - this had a somewhat noticeable effect on the smell and taste.

  • 1
    How did it smell? – chthon Jun 15 '17 at 9:18
  • Pediococcus Damnosus will overproduce glucan and spoil products by increasing their viscosity microbewiki.kenyon.edu/index.php/Pediococcus_damnosus – Philippe Jun 15 '17 at 14:27
  • all of them ;-) – farmersteve Jun 21 '17 at 20:44
  • Now I've been unable to remove the colonies from the interior of the PET bottles, even rinsing with Sodium Percarbonate. I wonder if this warrants a new question... I'll see if I can figure it out myself first. – rayzinnz Jun 24 '17 at 2:27

Lactobacillus breques is the most common one, followed by Pectinatus spp. The latter and Zymophilus can grow in pH between 4.3 and 4.6, with ethanol below 5%.

Other ones are:
Pediococcus acidilactici
Pediococcus damnosus
P. dextrinicu
Acetobacter spp.
Pediococcus cerevisiae
Acetobacter spp.
Lactobacillus spp.
Pediococcus cerevisiae
Gluconobacter oxydans

BTW 'spp.' is short hand for 'species'. As in "Lactobacillus spp." means all kinds of Lactobacillus and his brother will be found as contaminants.

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    Saccharomyces is not a bacteria its a fungus. – barking.pete Jun 15 '17 at 12:45
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    Interesting list, but will they all ruin a brew? More details on each would be appreciated. Thanks. – Philippe Jun 15 '17 at 13:21
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    Ruin is in the tongue of the taster... – Pepi Jun 16 '17 at 9:18
  • Well think I'll need to drink this infected beer for good health, and I quote from Wikipedia page on Lactobacillus brevis "Ingestion has been shown to improve human immune function" :) – rayzinnz Jun 22 '17 at 4:10
  • How would one (simply) determine the infection of the beer was actually down to L.brevis? – barking.pete Jun 22 '17 at 8:10

A good article about bacteria and beer brewing can be found in this link:


Its an article in a blog about sour brewing. But if one scrolls down halfway(ish) the author discusses other biological agents and their preferred brew environments - and the sort of tastes/odours associated with them.


Note that apart from bacterial infections you can also have mold infections. I've seen some weird stuff floating on top of the beer and in the krausen over the years, and quite a few times that was some sort of mold.

  • Beers, by their very nature, are always infected with mold. – barking.pete Jun 22 '17 at 8:12
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    Barking Pete, I respectfully disagree. Unfiltered beer contains yeast, not mold. Yeasts, molds and mushrooms are all fungi, but they are not the same. Yeast is not a mold, just like a mushroom is not a yeast. – Frank van Wensveen Jun 22 '17 at 14:10
  • FvW - I accept your point. I confused "mold" with "fungi". My bad. – barking.pete Jun 22 '17 at 18:52

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