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Dead Yeast?

So last Friday night, I decided to make the jump from extract to partial mash-
Sounded fairly easy, I got all the malt crushed for my oatmeal stout and followed NB’s guidelines for how to carry out the process. I got through the first part of the boil, and went to set the mash in the oven to rest, only to find out that my oven doesn’t go below 170F. After the one hour, I proceeded as usual with the extract/hops cooling and transfer to primary.

I added yeast Nutrient towards the end of the boil, and pitched my yeast (Re-hydrated Lallemand Windsor Yeast (Store was out of Safale S-04))

Activity started that night, and was going strong the next morning, but by Sunday, airlock activity had stopped, and by Monday, the Krausen had fallen back into the wort. I know, I know- The airlock is no indicator of progress- Originally, I thought maybe because we had one day that got up to 85 that my yeast had been killed off, so I bought another packet, sanitized and pitched it. (That one didn’t even take off…) But then I read that yeast doesn’t die from heat until about 120-140F, and that most likely the only adverse effect would be off flavors from the higher temperature.

So now I’m wondering- Is it possible that my mash temperature was too high for too long, and all the sugars have become too complex to ferment? I’d appreciate any help you guys can give-

Thanks,

No, you pitched a second package of yeast into a wort that was already beer and nearly all the sugar has been converted.

Not sure what your fermentation temps were, but unless you were unusually cool, it would not be unusual at all to have the majority of fermentation done in a couple of days. Especially if you left the fermentor in an area with ambient temps in the 80’s. You did not kill the yeast, but you sure let them go faster that is good for the flavor of your beer.

So, do you think the mash temperature really affected it at all, or is it most likely just the higher ferm temperature sped things up?

If ambient temperature was up to 85°, and you weren’t using some method to cool the wort, your fermentation was done. Vigorous east activity in a moderate OG beer will raise the fermenting temperature 5° to 8°.
My oven doesn’t go below 170° either. I partial mash on the stove top. For making bread I heat the oven to 90°, turn the power off, and turn the oven light on to keep the oven at 100° for the 1st and second rise of the dough. Same technique can be used for wort. Except for higher starting temperature.

The mash temp may have affected it, but your FG will tell you that. I doubt you denatured all the enzymes, but you may end up with a high FG. OTOH, the fermentation temp is a major issue. You may end up with a beer that has a hot, alcoholic, almost nail polish remover flavor. Only time will tell. In the future, for the best beer get the temp down to no more than the mid 60s before pitching. Try to maintain temps under 70 for at least the first 3 days.

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