TexLaw said:
However, there is a downside to mashing longer than required. The enzymes are still working to make a more fermentable wort. The alpha amylase is still breaking down the forked chains into more linear chains, and the beta amylase is still chewing up the linear chains into maltose. So, if you mash longer than required to convert, then you may very well be losing mouthfeel that you wanted in the beer, increasing attenuation, and possibly throwing your beer out of the balance you wanted. TL
On the other hand, you could be reducing the excessive mouthfeel that you don't want, increasing the attenuation, and bringing the beer into the balance that you wanted.
I prefer Palmers description. "the brewer is working the mash conditions to produce the desired profile of wort sugars."
The only way to really know is to experiment to find out what you like.
Palmer also says "At a higher temperature, a stiffer mash and a higher pH, the alpha amylase is favored and starch conversion will be complete in 30 minutes or less." I believe that this should be "At a higher temperature, a stiffer mash
or a higher pH, ..." as any of these factors will affect the conversion.
Another factor is the quality of the grain crush. Undercrushed grain takes longer to convert than well crushed or overcrushed grain.
Then there's the sparge method. If you fly sparge without a mash out, the enzymes will still be working their magic well into the sparge, whereas with a batch sparge, or mash out followed by a fly sparge, the effective mash time will be reduced.
Lastly, I can't possibly mash for less than 60 minutes because that's how long it takes me to heat the sparge water.
-a.