Pre Mashing

I have started all grain brewing and though not much, it is still more time consuming.  What affect would I have on the final quality of my batch, if I were to mash and sparge a few days to a week prior to brew day? 

It would be a Nasty Smelling Sour Mess and everyone around you would ban you from ever brewing again! No Seriously! If you don't boil the wort immediately after mashing, The wrong bacterial will start to grow. Which makes for a Nasty Smelling Sour Mess.

I started a brew session one evening around 5pm. Had a stuck sparge, which made the sparge go deep into 11pm. I was tired so I called it a night planning to start the kettle around 7am. It had a foam head on the wort, and had the most nasty smell. NOT GOOD!

Hope this persuades you against it. It was a big waste of my time, and I feel safe saying it will be that way for you also.

Cheers
Preston

I had a similar experience.  I had bought my grain (crushed at my LHBS) and had to wait a couple of days before brew day.  I didn't notice anything wrong with my brew at the time of mashing and boiling, but when I fermented, it starting giving off an abnormal odor.  I went ahead and bottled it, not knowing what had happened, and after even a couple weeks in the bottle, even though nothing blew their tops, it had a very foul flavor and odor.

I not only recommend getting your grains the morning of brew, or late the night before, but keep them in an air tight container with some kind of desiccant or something to help keep moisture under control until you are ready to use them.

Happy brewing
Steve

My favorite description is "the smell of death" and it permeates the entire area.  If you have doubts, save your spent grains in a tub next time.  And that's just moist grain with most of the sugars stripped out.  I would fear sugar-rich fully soaking grains would be much worse.  Egads.

Thanks guys! 

If you've mashed and sparged, surely the grains will be spent, (and ready to be thrown away), and you will have collected the wort in some other container?
Due to the temperature of the mash, there would be some pretty lively bacteria in your wort, and unless you boil it straight away, they'll continue to multiply if left overnight, producing the hideous smell mentioned.
Having said that, I don't know what the effect might be of storing the container in a REALLY cold fridge (near to freezing, in order to stop the bacteria from multiplying) would be. It might be worth an experiment some time, if you're desperate for time.
PB

If I do grind early-a grain mill was my first toy-good buy.  I grind into a spare bucket and snap on a lid right away. Never an issue.

I tried starting the mash right before bed on a Friday and brewing first thing when I woke up.
Once.
Never again.

In food service they refer to the "Danger Zone" as between 40 and 140, and anything left in that zone for more than four hours should be thrown out.
Granted the boil will kill off anything that wants to make you sick, but the nasties can (and will) leave a flavor imprint behind.

Sour mash whiskey is one thing, sour mash beer.... I'll pass.