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Old 01-06-2011, 03:33 AM   #1
beninan
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Default Good wat to determine infections in harvested yeast?

EDIT: Good way to determine infections in harvested yeast?

Several weeks ago, I decided to try harvesting and washing yeast from a finished batch. I didn't prepare for it on kegging day, and had no sanitized mason jars or anything, but whatever, its US-05 yeast and I wanted to collect and wash it mainly to get a feel for the procedure. It has now been sitting in my refrigerator with tap water, in an old unsanitized (but cleaned very well) honey jar.
I'm not worried at all if this goes bad, like I said, I just wanted to get a feel for the procedure.
I've been thinking about making another batch and making a starter with this (of course, I will have new yeast on hand if it doesn't pan out), but I'm wondering if there is a good way to determine if the yeast/starter has an infection? Would it taste sour or spoiled? Would the starter not kick off?
Even if I decide to throw this out and recollect some more yeast using some good sanitation techniques, how will I know if that yeast is free from infection?



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Old 01-06-2011, 11:30 AM   #2
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Color and smell are good indications. If it seems darker (brown instead of creamy white) or if it just doesn't smell right (sour or not like beer) dump it.



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Old 01-06-2011, 12:12 PM   #3
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Plate it on some wort enriched media. If the colonies growing don't look like yeast then it's infected. That's the most definitive way that I know to tell.

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Old 01-06-2011, 12:43 PM   #4
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+1 to the plate method. In my opinion, that's the most definitive way to determine if it's infected or not.

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Old 01-06-2011, 01:58 PM   #5
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Yeah, I don't think the smell test is accurate - yeast can make some weird smells and flavors when you continually supply them with oxygen in a starter.

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Old 01-06-2011, 02:03 PM   #6
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I sniff it.

If it smells like the beer I want to make (meaning I probably didn't wash the hops off well enough) than I use it.

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Old 01-06-2011, 02:11 PM   #7
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Quote:
Originally Posted by kanzimonson View Post
Yeah, I don't think the smell test is accurate - yeast can make some weird smells and flavors when you continually supply them with oxygen in a starter.
I guess you need to know what you're looking for.
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Old 01-06-2011, 02:18 PM   #8
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Not to be presumptuous, but it seems like plating is a little out of his league.

It it acts like yeast in the starter (ie: clumps settling near the bottom, normal looking krausen, somewhat normal smell) then you should be good to go. Remember that when you wash yeast, you only add boiled water so there should not be any food for any bacteria to eat, only sleeping yeasties waiting to wake up.

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Old 01-06-2011, 11:43 PM   #9
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Thanks everyone. I don't have the equipment, or full knowledge, on how to plate a culture, so I'll have to do some research if I decide to try that. I haven't opened the jar to smell it since I first put it in there, and the color looks the same as it did when I harvested it. The water used was unboiled, unsanitized, tap (city) water, so who knows what's in it. The container hasn't exploded from it re-fermenting, so I don't think there was much in the water for the yeast to eat. I think I'll try an attempt at making a starter for this, maybe even use it in a simple and cheap SMASH, so not much is wasted if it doesn't turn out.

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Old 01-07-2011, 02:04 PM   #10
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Quote:
Originally Posted by beninan View Post
The water used was unboiled, unsanitized, tap (city) water, so who knows what's in it.
I would continue the science project just to refine your techniques, but not use it for a beer. The best water source would be in descending order:
1. Sterile as you can produce with an autoclave or pressure cooker and mason jars.
2. Almost sterile, sanitary water using home canning techniques and mason jars.
3. Regular tap water.
4. Left over dog bowl water.


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