Yeast pitched at a high temp

So I brewed an American IPA yesterday and pitched wyeast 1968.  I mistakenly pitched the yeast at a high temp.  My thermometer said my wort was down to 72 degrees before I transferred to my fermenter.  But when I looked at the fermometer, there was no temp that was registered (it goes up to 78 degrees) so I assume that it was much higher.

4 hours later, a really dense cake had formed an inch or two below the surface with no other real visible activity.  At that point the temp had hit around 78 degrees on the fermometer.  See the attached photo for a visual.  This morning (18 hours later), the cake has dispersed and there is a light krausen on top with not much bubbling activity.  The temp is now at 66 degrees (I threw some wet t-shirts around it over night to cool).

From what I understand, wyeast 1968 is supposed to have vigorous activity so I'm a bit concerned.  I don't think the wort was above 90 degrees when it was pitched, but I can't be sure.  Did I kill my strain?

One other concern I had was the strain itself.  When I pitched, it was half liquid and half paste.  I had to push it out like toothpaste to get it in the fermenter.  From what I've read it seems that's okay, but I've never experienced a strain that did that.

You didn't kill it.  If you had killed it right away, you'd have had no activity.  Is it dead now?  I doubt it.  You might have some off flavors from fermenting at too high of a temperature.  Since it's an IPA, the hops will probably cover up most of the off flavors if you have any.  I wouldn't worry about it.

Thanks for the reply.  I'm sure most of the yeast is under stress.  And even now, 24 hours later, there isn't much bubbling activity.  I re-pitched, just in case.

I'll have to re-calibrate my thermometer to make sure it's accurate.

So here's a brief follow up with a math question.

I re-pitched my yeast and activity seemed to be great this week.  Krausen is falling now so I'll be taking a gravity reading within the next few days.  Hopefully the beer doesn't get too many esters.

I was curious if there was a way to calculate what my "starting" temperature was?  Since my thermometer was incorrect when I chilled the wort, I'm concerned that it was actually higher than I originally thought. It took 5 to 6 hours to drop from (x) degrees to 78 degrees in an environment that is 64 degrees.  I have no idea how I would calculate this---sorry, studied as far away from math in college as I could.

I need to know so I can determine what the proper gravity reading was.  My reading was 1.053 when it should have been closer to 1.060.  If my temperature was indeed over 115, I'll have to adjust my gravity reading.

Anyone have any thoughts?

bobo1898 said:

I was curious if there was a way to calculate what my "starting" temperature was?  Since my thermometer was incorrect when I chilled the wort, I'm concerned that it was actually higher than I originally thought. It took 5 to 6 hours to drop from (x) degrees to 78 degrees in an environment that is 64 degrees.  I have no idea how I would calculate this---sorry, studied as far away from math in college as I could.

Click to expand...

The math is heavy but you can do a simple test using wort or sugar water at some temp and measure how long it takes to drop 1 degree for about 5 degrees.  It should be linear taking the same time to change and 5 degrees is 5*1 degree.