I do overnight mashes and the only way it would get sour is if it drops below 140 for an hour or two. My mashes usually lose about 10* overnight, most of it near the end of the mash. My beers taste completely "normal" and my scores reflect this. I've had to adjust my starting mash temps though because the wort becomes VERY fermentable due to the lower temps it reaches. You won't denature all of the beta amylase, even with a 158-160* mash-start-temp.
If you want souring, I suggest starting in the mid-to-high 140's and it will drop below 140 at some point. You can also do an all-day mash so you can monitor the temp drops and sourness, then stop it and sparge right when you get it where you want it. I do all-day mashes the same as overnight. It's just time, no matter what part of the day you do it.
Den Faaborg Bryggeri
Originally Posted by davekippen
Open log Fermenting and gas-can secondary?? I am planning my next brew right now!!