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Old 06-20-2011, 03:36 PM   #1
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Default How Do I Know Whether Reused Yeast is Infected?

I am going to attempt my first brew with reused yeast: Wyeast 1056. I used it in a pale ale and want to brew an IPA with it. The yeast has been in the fridge in a sealed container for about 2-3 weeks now.

My brewing plan is to pitch that yeast into starter at least 24 hours before brewing and then brew up my new IPA.

Maybe I'm just being a worrywort but how will I know whether this yeast is infected? I'd hate to pitch infected yeast and not know about it until a few months later after eventually drinking my new brew. Are there any telltale signs (i.e., smell, lack of activity in the starter, etc.) I should look out for before pitching it into the new beer?

Thanks all.

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Old 06-20-2011, 04:47 PM   #2
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Your best bet would be to taste the spent starter. If it tastes infected, then your yeast sample is the likeliest source. If it tastes normal, it's unlikely that you'll have any infection in your beer.

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Old 06-20-2011, 06:25 PM   #3
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Actually, the spent starter will prolly taste bad regardless due to O2. I'd pour the yeast into the starter and then take a small taste of the actual yeast from the container you poured FROM. The yeast should smell and taste good.

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Old 06-20-2011, 07:49 PM   #4
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Originally Posted by ThePearsonFam View Post
Actually, the spent starter will prolly taste bad regardless due to O2. I'd pour the yeast into the starter and then take a small taste of the actual yeast from the container you poured FROM. The yeast should smell and taste good.
There's a world of difference between oxidized beer and infected beer, and that difference should be readily apparent.

Tasting the contents of the storage container will detect contaminants if they had already wrecked havoc on the sample, but there's no way a taste-test will pick up on a small infectious colony living in a larger population of dormant yeast. As soon as that small infection gets pitched, however, it may quickly out compete the yeast.
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Old 06-20-2011, 07:59 PM   #5
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if it formed a pellicle or firm-filmy bubbles, it's infected

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Old 06-20-2011, 08:02 PM   #6
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if it formed a pellicle or firm-filmy bubbles, it's infected
Yeah, that would be a hint

...of course, just because there isn't a pellicle doesn't mean that it's not infected.
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Old 06-20-2011, 08:05 PM   #7
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I reuse yeast all the time, lots longer time frames than that. I make a starter, pitch the yeast, then taste the oxidized (yuck) fermented starter. If it is infected you can smell it! If it is infected you can definately taste it.

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Old 06-21-2011, 10:36 AM   #8
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I agree that there's a world of difference between oxidized and infected. I would definitely taste the starter if it were from a vial or pack, but it's reused. If the cake is infected, then you'll most likely smell and taste it by sampling the yeast too. Either way works for reused yeast.

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Old 06-21-2011, 01:02 PM   #9
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ive read on here that your starter will have a sour like taste to it and it doesnt taste good either. I have never tasted my starter before but just a heads up.

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Old 06-21-2011, 01:35 PM   #10
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Starters don't taste good because of oxidation. The goal is to grow yeast cell counts, not make beer, so we intentionally allow O2 into the process. The result is more yeast and a bad taste...

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