I made a porter with Trois last November and kept a jar of washed yeast. I recently found it again in the back of the fridge and decided to see if it's still alive to make another IPA. I set the jar out and as it warmed it became active, like it almost blew the top off the jar! I poured off the liquid when I put the yeast into the starter and tasted it. Suuuper sour. Now I'm not sure if I'm growing yeast, or some other bug? I don't want to waste a whole brew on a nasty beer, but I don't want to throw away a good yeast either. Anyone with any knowledge on this?
Not much to go on. You say you put the yeast into a starter, so taste that after a few days. If that is getting sour, than I would guess you have some contamination. See how it plays out.
I poured the liquid off the yeast in the jar that it was in for 5 months. That's what was sour. I'm going to decant today and see how it is.
I've had trois create a lot of acetic acid in the presence of oxygen (bucket) for 2 months. That could be what's happening if the acidity seems kinda vinegary to you. Although I'm not sure why the starter was active when it warmed. Could be infected. Brew a small Batch and see what happens?
Agree with @psnydez86, chances are acidity was brought on by aeration. Test a small batch and carry on to a larger size if you like it. Could be contaminated but also starter worts aren't the best judgment of a full batch. Do a small batch and see what happens.
