If I were to mash for four plus hours

would there be a problem here?  I don't think that's enough time to let the temp drop to dangerous levels but I'm wondering if letting the mash sit for that long will have an effect on the beer?  Say if I'm shooting for a medium bodied beer am I endangering that possibility by my mash sitting that long and undoubtedly losing some heat along the way?

I'm no mash guru, but have read that 60-90 mins is usually enough, and that longer is fruitless.  A given mash has XX enzymes available to convert YY starches.  Maybe the question would be is 4 hours enough to allow souring or serious ill effects? 

One of the "tricks" I employ in my big beers is a very long mash and 3-4 hrs is not unheard of.  I do this to achieve the maximum fermtability so I can achieve the maximum attenuation possible.  That is needed when you are brewing with 1.130+ wort.

Conversion is a matter of time and temp and the standard 60-90 minute mash is adequate for most beers.
The risks:

• Making your wort too fermentable resulting in a drier finish (lower FG) than you would wish.  Solution here is to mash higher, how much?  that depends on your process and timing on your equipment,  try and see.
• Excessive time in the mash can result tannin extraction, though I've not noticed this happening to me.  Tannin extraction is more dependent on mash pH.
• There are all sorts of "bugs" on grain.  It is possible to develop an infection, that you will kill off in the boil, that imparts a flavor, especially if your temp dips below established critical levels.

many people are known to achieve good results mashing overnight

Fred

Thanks for the responses.

Yeah my question really centers on my starting my mash and then going to an appointment that I can't break that will take around 4 hours to do and then sparging when I return.  As I understand it after the enzymes are converted they're converted but the higher the mash temp the quicker this happens.  The lower the mash temp the longer it takes but it allows for everything to convert.  I'm shooting for a medium bodied beer so mashing at the higher temp will keep the beer where I want it.  My concern was really around ill effects to the beer.  What about this, what if I am able to sparge before my appoitment and then boil when I return would there be issues with this? 

Rules are rules, and they are made to be broken.  I break a number of them and still turn out award winning brew.  It is possible to have ill-effects to your beer from a normal brew day.

Go for it, while risk is there I don't think it is substantial.

Just let us know how it works for you.

Fred

If I were doing it, I'd mash and lauter/sparge and boil it later.  At least you'd eliminate the unknowns of grain contact time and extracting things you don't want.  And you'd get the mash profile you desire.  Delaying the boil 2-4 hours must happen all the time when people run out of propane and they've drunk too much to run to store right away. 

Well, I didn't wake up in time to really get everything going so all I had time to do was get everything set up.  By the time I got back, around 4-4:15 I turned on the oven to start heating the initial strike water.  Everything went okay, I guess, but it was a late brew day (night) of course part of that had to do with the my wife's car battery dieing and me having to go get her right in the middle of sparging.  I had the first runnings in the kettle and had just put the first sparge volume into the MLT.  Then I had to go jump SWMBP (there are about a million jokes there, I know this so run with it if you must but know that I thought of it before you did).  After an hour or so I got back and finished up but it was a long night.  I exceeded all my numbers though, could there be something to letting your sparge water sit for a bit? 

An extra long mash will do two things for you

• Get you a couple extra points (higher OG and increased efficiency)
  
• increase fermentability of the wort resulting in a lower FG that that which you would otherwise have gotten.

The increase in efficiency is generally not worth the time and the increase in fermentability (and the resulting attenuation) is only needed in special circumstances.

Fred

Wow, was I surprised to see the exact same question I had yesterday!  My delay/break was only due to HAVING to watch Steelers vs. Vikings and wondered how best to break up the brew sesision into pre-game and post-game efforts.  I would have liked to have finished the sparging by game time and starting the flame back on the boiler maybe between 3rd and 4th quarters. Alas, I only got the mash going and its 60 min were to be up around game time.  I had heard of brewers mashing overnight as a nice headstart on their AG brew day, so I felt ok to let it sit for another 1:40 until half time.  At the end of the 2:40 mash, my temp was still 150F, so I'm not worried; I wanted it at 155, but I missed that at the beginning anyway, so I really didn't lose due to the long mash.

I sparged at half time and should have stopped there, but I didn't - I started the boil and found myself running in and out, trying to catch both the game and the brew.  The boil didn't roll until well into the 3rd qtr (starting my 60-min counter) and thankfully, my hops schedule was only 1 addtion at the 30-min mark and again only at 0 so I could mostly watch the game, especially the 4th qtr!

I got about .005 more points in my OG (1.070 vs 1.065 anticipated) and might be a little dryer than I'd hoped.  Bottom line, I accomplished both and it was a great day all around. Go Steelers!

Cheers!
Rick