Has anyone split their brew session into two different days? I was thinking about doing a BIAB mash in the evening, and then the next morning completing the boil process.  
The benefit to me is breaking a 5 hour session into a manageable 2 hour evening session, and then a 3 hour brewing session the next day.
Any issues with taking this approach?

I have split, but not that way. I often mash and boil, then pitch the yeast the next day after the wort has cooled. This works well for me.

But, I think you can find discussions about succesful overnight mashing.

Until you reach a boil to kill off any nasties, you still have a very high potential for nasties (define that however you wish) in your wort. I wouldn't recommend it. They will chew on that wort overnight.

Having said that... I did it once myself with good results. After collecting the preboil volume in my brew kettle, I put it in my chest freezer set for the mid 30's. Any bugs in there would have been very slow to do anything to the wort... kind of like putting leftovers in the fridge instead of letting the sit on the counter. It took forever and a day to get 6.5-ish gallons to a boil from that temp on the stove top.

I did read somewhere to bring the wort up to 180 degrees to pasteurize it... Before letting it sit overnight. But I'm still not sure if I want to try it.

I've seen some talk on this subject on HBT. There are a few advocates of this style over there if I am not mistaken.
I'd make doubly sure the mash tun was thoroughly sanitized and then report back to us your findings and observations.
Don't we always quote "Mr Beer, My Beer, My Way ? "

I've got to agree with Banjoman. If you wanna do it, do it.


That seems reasonable.
The thing you want to avoid is anything that would lead to a sour mash when you don't want one.
Sanitizing some of the preboil equipment and pasteurising the wort seems reasonable to me.

Exactly. Lacto lives naturally on the surface of grains, right? Unpasteurized wort will sour. I just don't know how soon.

yeah, sounds about right, prof and pudge... they were just talking about sour mashing on a recent episode of the sunday session (either the one with black star co-op or the one with tide brewing/trophy fire, i think)... once the mash (or the wort, in this case) sours there's no going back. but i think sour mashing happens around 115° F. so then the question i have is... if vat pasteurization occurs at 145° F for 30 mins, why would the runnings (which have been holding above 145° F for an hour) not be pasteurized? when the wort drops below 145° F when it's sitting there cooling, that would be when the bugs come to party... but, i have no idea... just playing devil's advocate.

The time between mashing in the evening and brewing in the morning is not that long. I think Lagerpmp might be okay with no modifications to his process. However, changing the time between mash and boil is already a modification. So, is anything required to compensate? I think just reasonable steps.

8 hours or so? might not be a enough time to start to sour, but who knows. i don't know. but, i would think so long as a tight fitting lid is on, it'd be fine. nasties can't climb... just hitch rides on specks of dust.