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Need advice about testing for infected yeast.

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slayer021175666

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I keep top cropped yeast in mason jars in the fridge. I have had a couple here lately that I think may have been infected and soured my beers. I normally just take it out of the fridge first thing on brew day, let it come to room temp while I brew and pitch it directly when the wort is cool enough. The one I have now looks fine but, I am suspect. Could I pitch the whole thing in a starter and smell and taste it after it ferments? It seams like a good way to test it but, IDK for sure. Is there another way to find out if its still good clean yeast before, I potentially ruin a good batch with it? I don't have a microscope and the only info I'm finding online just talks about using one. Seems like there would be another simple yet, fool proof method that doesn't involve a microscope.
Thanks in advance.
 

ba-brewer

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No for sure test, but I sample a little of the beer on top of the yeast to see if it tastes normal. I am mostly looking for phenolic flavors in known non phenolic yeast. Can also look for tartness to a certain extent that way. I use only enough to taste just in case it is funky.

I also give the jars of slurry a sniff test as well. Again I am mostly looking for phenolics but it can identify vinegar, acetone and dead yeast smells.

I think I have had cross contamination from my mason jars in the past even though I washed and sanitized in starsan. I now toss my jars in the pressure canner for 20min and store them filled with sterile water. I am sure boiling water would work as well but I have a canner.
 
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slayer021175666

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I top cropped and filled jars with bottled distilled water. Do you think it would be any different?
Side thought: Maybe I should go back to storing it under beer instead of water?
 

day_trippr

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Years ago an HBT member with a microscope and video cam posted a short flick showing a yeast cell exposed to distilled water.
It did not end well for the yeast cell. So, from that whole "cell wall osmotic pressure" thing...I would stick with using beer and definitely not distilled water.

As for the OP's conundrum: I can't offer much in the way of experience with storing and pitching top-cropped yeast as I use 6.5g glass fermenters which makes top-cropping a challenge. Thus I've literally only done it once - using yeast captured via sanitized blow-off gear [I digress: the batch I pitched it with was a wild and crazy ride considering it was LA3 - not known for aggressive fermentations. It worked out fine though].

Anyway, here's my take on such matters: If in doubt, pitch it - down the drain.
I've done that plenty of times with yeast I've acquired via one method (over-builds) or another (cake).
If I had any doubt, I tossed it, because the yeast is way less costly than a dumped batch of neipa, and it's one fewer thing to stress about...

Cheers!
 

Vale71

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Isotonic solution and not distilled water is the best medium for long-term storage of yeast. Beer is the best medium for short-term storage, meaning 24 to 72 hours or thereabouts.

The simplest way to test your yeast stock without using a microscope is by using a selective medium culture like this one:


What you would do is inoculate a vial of culture medium with a drop of your stored yeast and incubate it for several days, at best in an incubator at 27°C. If the solution changes color to yellow then you know that the yeast is contaminated, without a microscope you just won't be able to get a more specific identification but that's all right if all you're going to do in that case is throw the contaminated stock away.
The downside is that the medium is not ready-to-use but must be mixed with water and light-colored beer and then sterilized in an autoclave which is something most homebrewers don't have handy. 🤕
 
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