[fredthecat]

Ever smell a mash that's been left overnight in a cooler? It usually has a bit of a lactic twang to it. I have done overnight mashes in my oven with the oven set at 170 degrees and that worked well.

i forgot to empty my mash tun one time for a few days (maybe 3 to 5). lol at that point it was significantly more than a twang. i think i posted here on how to get rid of the smell. it did work, vinegar, baking soda, PBW probably, i cant remember.

one data point indicating processes are for sure going on

I have done extended mashes (2-3+ hours) a couple times in my Anvil Foundry set at 150F or so, but never a full overnight, except when I once made a Berliner Weisse with some grain as the lacto agent (after regular mash, I brought up to near boil then pitched some grain and left it overnight until I reached my intended pH).

i actually really like 2- 4 hour mashes as it is a great way to really get high attenuation and i dont think it did anything to the flavour

[chumley]

I never overnight mash in my cooler, but I often wait until the following day to clean up. I can't say I have ever noticed a lactic smell to the spent grains after overnight. A couple of days is a whole different story.

[majorvices]

I never overnight mash in my cooler, but I often wait until the following day to clean up. I can't say I have ever noticed a lactic smell to the spent grains after overnight. A couple of days is a whole different story.

Interesting. A brewery I worked at one of the brewers couldn't get the mash out and waited until the next morning. When I came in the next morning the entire brewery smelled like spoiled mash. Just one night. Likewise, I have noticed it on my home brewery as well. I wonder what the difference is.

[denny]

I never overnight mash in my cooler, but I often wait until the following day to clean up. I can't say I have ever noticed a lactic smell to the spent grains after overnight. A couple of days is a whole different story.

Interesting. A brewery I worked at one of the brewers couldn't get the mash out and waited until the next morning. When I came in the next morning the entire brewery smelled like spoiled mash. Just one night. Likewise, I have noticed it on my home brewery as well. I wonder what the difference is.

Maybe ambient temp? I've never had it go lactic, either. Maybe because Chumley and I line in the NW and you live in the south? Maybe because when you're doing an overnight mash you keep it warm, as opposed to letting it sit at cooler temps when you don't empty the tun? Just a couple WAGs.

[chinaski]

Oxygen levels would probably be different in an intentional overnight mash versus a drained mash left overnight. 

[brewthru]

Ever smell a mash that's been left overnight in a cooler? It usually has a bit of a lactic twang to it. I have done overnight mashes in my oven with the oven set at 170 degrees and that worked well.

Ever smell a mash that's sitting in a bucket waiting to dump (for example, in the backyard compose pile)?

[Drewch]

Oxygen levels would probably be different in an intentional overnight mash versus a drained mash left overnight.

There are probably some square-cube law effects going on, too, with heat mass, surface area, etc.

Considering that a strong plurality of my recipes are farmhouse / sours anyway, a slight lactic twang wouldn't be out of place for me. 

But I do wonder, assuming your cleanliness is good, your tun has a lid, and your mash temp is in the pasteurization range, where you're getting enough bacteria to have that much effect after <24 hours.