I am trying to understand the nature of contamination in beer. I find it difficult to imagine (considering there are wild yeasts and moulds and micro-organisms in the air - aren't there?) a scenario where a beer is 100% free of contamination, or is this normally the case with a properly brewed batch? Or is it a case that when contamination is lower than some threshold we don't notice it and that beer is considered to not be contaminated?

I am interested because being new to homebrewing and educating my palate, particularly with regard to off flavours I often wonder whether I have some kind of contamination. But I would usually discount this if the beer is question is pretty drinkable, because I would have assumed that contaminated beer would REALLY stand out and not really the kind of thing easily confused with an off flavour, but considering what I was asking about above; could it be possible to have a small amount, or even a tiny amount, of contamination being responsible for off flavour if we define contamination as "above a certain ( detectable ) threshold"?

If that's the case then is it a case that we're trying to reduce contamination rather than avoid it, or is it possible to avoid it altogether - and is it a case that minute contaminations are common but to the degree that we eradicate these we are likely to get better tasting beers?

2 Answers 2


First, technically all beer is contaminated, since you pitch yeast. And yes, I'd say pretty much all homebrew (and even commercial beer) is contaminated to some extent. The type and severity of the contamination can vary, however.

  • So with the exception of sours or something do lower levels of contamination always improve the taste. I mean if all beer is contaminated to some extent then does it follow then that the better beers ( sought after / competition winning etc ) would generally have to have little or no contamination to be highly regarded. I'm asking because I'm always wondering whether it's that I'm too obsessive ... or whether I'm not obsessive enough ... about sanitation. Is it a case of a law of diminishing returns or is it actually an achievable goal to have virtually zero contamination :-) Commented Feb 28, 2017 at 21:57
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    Intentionally pitched microbes (yeast) wouldn't really qualify as it being infected, pedantic-ness aside.
    – brewchez
    Commented Mar 1, 2017 at 11:27
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    @byronasgur - Yes, the best beers will have the least contamination. Most bacteria/wild yeasts will make some contribution to flavor, and even though low-levels may be barely perceptible. they may be enough to make your beer less enjoyable than a less contaminated beer. This is why you need to pitch an adequate quantity of active yeast cells -- it is a race to see which microbes will consume the most sugar. When the yeast multiplies quickly enough, it crowds out and starves the invaders
    – jalynn2
    Commented Mar 1, 2017 at 18:43

YES. All biological contamination (infection) take time to do their thing. So yes there are levels of contamination. Acetobacter for example, can be at a range of non detectable to the palet to full on vinegar.

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