Originally Posted by beerbro
So I am still new to all grain brewing and have mainly been using existing recipes for my ag so far and I have only brewed 4 times. I was just wondering how you choose what temperature you should mash out at and the boil you do before the mash. I always see them at about 150 and 170 respectively with some variance. My question is how can the differences in temperature affect you beer and what they impart to it? Also how to you gauge what boil size you should be at? Sorry for being such a noob i am just still new to this stuff and i am obsessed with learning as much as possible about beer.
Well, you should never see a mash temp at 170! That's where you totally denature the enzymes after mashing to "hold" the profile- typically called "mash-out". It's not necessary, though, so that is why sometimes you see it sometimes you don't. Not everyone does a mash-out.
But you'll commonly see mash temps from 149-158, give or take a degree or two.
The short explanation is that there are enzymes that are temperature dependent, and those enzymes convert the starch from the grain into fermentable sugars. Some enzymes work better and more efficiently at cooler temperatures, while some work better at a slightly higher temperature.
Two that we brewers think about most during mashing are alpha amylase and beta amylase.
Beta amylase produces maltose, a fermentable simple sugar. It works best at 131-150 degrees. Alpha amylase produces maltose, too, but also more complex sugars (such as maltiose). It works best at 154-162 degrees.
Maltose is a simple sugar, meaning that making a mash favoring it (lower temperature) would give you a thinner bodied, drier beer; while flavoring alpha amylase in the mash would give you some more complex sugars (but simple sugars too) giving you a fuller bodied beer with more residual sugars in the end.
Most people want characteristics of both, so they "split the difference" with a mash of say 152. That will give a medium bodied beer with not much residual sugar but not too dry.
That's breaking it down to its most simple, so I'm leaving things out but that's the jist of it.