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Old 11-06-2010, 12:28 AM   #1
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Default Colonisation resistance of beer after primary fermentation

So, I've been wondering about this for a while now.

A lot of people cannot quit stressing how important it is to clean and sanitize everything, to the point where I'm starting to experience their concerns as a phobia rather than rational precautions.

One thing in particular bothers me: the fear of contaminating beer after primary fermentation. At that point, most of the substrate that micro organisms can feed on (simple sugars, organic phosphates) has been depleted, and replaced with alcohol which will kill most contaminants.

If a foreign lifeform where to end up in the beer, survives the alcohol and didn't starve to death, it still has to compete with the yeast still present. Billions upon billions of yeast cells to compete with mere thousands of contaminants. Competing for example for whatever oxygen is present which could go to turning alcohol into acetic acid.

So bottem line: has anyone ever had a contamination after primary fermentation?

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Old 11-08-2010, 03:56 PM   #2
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Update:

I've consulted my professor during class on food science, he said that the alcohol levels of beer aren't enough to kill anywhere near all contaminants, and that beer certainly does remain at risk of infection after primary fermentation.

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Old 11-08-2010, 04:00 PM   #3
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SO you answered your own question....thread closed.

Actually if you look around here, the overwhelming fear of infection tends to be the purview of new brewers. It's more psychological than anything else.

We had an interesting discussion about this last week....When can I stop worrying about an infection ?

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Old 11-08-2010, 06:24 PM   #4
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You have to remember that brewing strains were chosen precisely because they would produce consistent and pleasing results: most attenuation rates are in the 68-80%. This means that you have nutrients still available that the sacc can't transform into CO2 and alcohol. Other yeast strains are able to process the residual sugars, thinning the body and stripping the beer of its original taste. Brett is one of the bugs that can accomplish this. But I'd wager that a lot of ambiant wild yeast cannot tolerate the high level of alcohol and the low ph of beer, wich is why you can have the beer in contact with open air during bottling and come out fine. Brett also works very, very slowly, as does pretty much all yeast not specifically bred for brewing.

Does this mean that you should be worried ? Not really. Practice good sanitation procedures at all times and the risk becoems slim to none, with the emphasis on none.

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