Originally By Tony Ackland
Cooling the WortBefore you pitch the yeast, you need to cool the wort down below 26 ° C. You could leave it overnight to cool, but then you risk letting an infection get started. Its often better to force-cool the brew down. The rate and length of fermentation is adjusted by the pitching temperature, which in turn can influence the flavours.
Jack writes ...
If you are making a mash using grain (corn, rye, malt, etc) you should try and cool the mash down to 70F in under one hour. Otherwise, you are allowing the production of a chemical called DMS (dimethyl sulfide)- this is a chemical compound that gives beer/mash a buttery/ butterscotch flavor- in some dark beers, it's okay- in light beers and whiskey mashes it's a problem. Over time DMS is reduced into various other sulfur compounds- some will form a rancid butter flavor/oder, others will be estery (solvent flavor). By cooling the beer/mash quickly, you inhibit the formation of this compound. And, yes, the nasty flavors DMS can make will transfer over into the finished spirit.
And, that's the prime time for an infection to take over. The rule is: cool to 70F as quickly as possible, and add your yeast as soon as you get to that temp.
The inside of the chiller has to be spotless and sanitized to keep from contaminating the (then cooled) wort on its way to the fermenters.
I've been using and cleaning this thing for 10 years and have NEVER had a contaminated batch.
The vinegar/water mix makes it shine like a new penny!
This method was told to me by a PhD Brewing Chemist who'd been doing this for years. It really works!