I asked before and got some help and have done some reading since. The temp in my mash jumped from 175 to about 195 after I put the lid back on. How much damage did I do? Some things I've read since suggest that it may be okay since the density of the grain(and, in this case, about 8lbs of cooked pumpkin) may have kept the center mass of the mash somewhat insulated. Opinions? There were some spices(cinnamon, nutmeg, ginger, cayenne) added so it may mask any tannins.
@dana's answer is full of good info. I'd only make one change: if I were you, I would just wait it out and see what happens. It's possible the beer is ruined, it's possible it's the best beer ever, but it's probably somewhere in between.
Tasting the final beer will be an excellent learning experience, if nothing else. Learning from our mistakes is just as important as making great beer, in my experience.
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If you measured 190 F at any location in your Tun, I would expect the average temp to exceed 170 F. Pumpkin is mostly water and I don't see it as a significant insulator.
Enzymes are little chemical keys that convert the starch in you pumpkins and grain into sugars that the yeast can consume. There are several families of enzymes and each can only tolerate a certain amount of heat before they denature, or fall apart. Once they denature they cannot be recovered.
All enzymes used in brewing denature at about 170 F. If you held your mash above that temperature for any length of time your enzymes denatured without an opportunity to convert the starch into sugar.
Without this important step, your wort will be composed of mainly starch. I would expect a very high final gravity, and a very cloudy beer.
I hate to say it, but you won't be able to drink this beer.
EDIT: I'm changing my recommendation, if you don't need the equipment to keep brewing. You should definitely ferment this out and see what happens. If you do this, please update the question so we can all learn from your experience.
P.S. - I think there might be a salvage technique you could apply if this ever happens again. IF you accidentally kill off the enzymes, you should cool the mash back down to an appropriate temp (say 145 F) and add Beano. Beano has the necesary enzymes for this job. Periodically perform an iodine test to measure your conversion. When the mash has converted "mash out" or raise the the temp above 170 again to denature the Beano. (Don't skip the last step or the beano will never quit, and you'll have a super dry beer)
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