Originally Posted by unionrdr
That's not what I was refering to. it was to the previous discussion above about initial fermentation vs reproductive phase making more 0ff flavors. I was giving my opinion on that,not rehydrate temps.
And it doesn't cool down that fast on it's own. It won't cool down from 90F to 75 or 80 in 30 minutes in a pyrex measuring cup. I'd have to use a small ice bath or something.
I just checked this with my Thermapen. I started with a cup of water at 95 degrees in a 4 cup measuring cup (Note: I even made sure it held at 95, i.e. the measuring cup was warm too). 30 minutes with Saran wrap on top and it got down to 79 degrees. My house is currently at 68 degrees. If you started at 90, as per the low end of the manufacturer's instructions you could easily get to within 10 degrees of common ale pitching temps. It might depend on the measuring cup too, though.