I did my first overnight mash yesterday. A big 8% Irish Red for St. Pats 2009. I mashed in 11pm on Thursday and started the sparge between 6-7am Friday morning.
I do 10 gallon batches in a standard Home Depot 10 gallon Igloo round cooler. It only lost 4 degrees overnight left indoors at room temperature (154 down to 150). I draped an old sleeping bag around the top and sides.
Here's the upside to an overnight mash, IMHO with just one overnight batch under my belt:
* OG about 6-8 points higher than identical recipe done three times in the past with 60-90 minute mash
* No difference in color, flavor, or mouthfeel
* Quck clear vorloff
* Ability to mash a second batch when the overnight batch is in the kettle the following morning, if desired.
* Consider decreasing the heavy roasted grains (black patent, carafa II, etc) a bit to decrease the chance of extra astringency developing
* With a 60-90 minute boil, plan to be done and cleaned up by 10:30am. Sweet!
This will be a great option for brewing in the summer when I want to avoid standing over the kettle in the middle of a hot day.