Mash Temp/Conversion

So I've been brewing all grain for a awhile and should know this, but was wondering if you mash at beta amylase, say 145, and convert all available starch, then go up to alpha amylase, say 158, will you get the long chain sugars in your wort that give you a thicker beer, or does the earlier beta amylase rest convert those long chains into short chains and thereby making your wort more fermentable and thinner.

Thanks for any insight,

Jim

Beta amylase can only chop maltose from what's known as the "reducing end" of a poly-glucose chain. It can completely convert the amylose form of starch since there are no branches. Amylopectin has branches in the chains, so beta can only work from a reducing end up to the branch point (actually a few glucose units before the branch), and then it gets stuck. The chains past the branches would never get converted. So, you cannot convert all available starch with just beta amylase.

Alpha amylase can chop up the poly-glucose chains at random points, resulting in random size glucose chains. Alpha can also not break the chains near a branch point, but can attack the chains from either end, and between branches if there are enough glucose units between branches. You need at least a little alpha amylase action to get a fully fermentable wort (just maltose, glucose, and limit dextrins.) Alpha amylase will work at temperatures within the optimal temp range for beta amylase, but the action is much slower. Also, alpha amylase is not as efficient as beta at creating the fermentable, small molecule sugars.

Once you have cut up the long chains, you can't put them back together to get a less fermentable wort. Fermentability only increases with increasing time (increasing enzyme action), and chain length continuously shortens. What you get at different temperatures is different rates of action for the two enzymes, and at higher mash temps the beta amylase gets denatured faster, so that most of the action comes from alpha amylase. If you want some residual longer chains, just mash at higher temps, but not for too long. Or, put in some malt that can't be converted as well by the amylase, like dextrin malt, crystal malt, or roasted malt.

Brew on

That is an extremely good question AFAIK, beta amylase can convert long chain sugars into short chain ones, but only at temperatures where it's not completely destroyed. At 158 it might be mostly, if not entirely, gone. This is why most recipes call for 153-154 degrees, where both enzymes are active (even if not at full capacity). Then again, I might be completely wrong, and I'm really curious if someone with more knowledge of chemistry could shed a light on this.

Guys, thanks for intelligent replies. So see if I get this. Clearly if you mash at higher temp. you will get unfermentable long chain sugars and end up with a sweeter thicker beer, e.g., stout.

But, if you miss your, say 158 temp, and hit 145 or so, on dough in, you risk losing the long chain sugars even if you go up eventually get upto 158.

So the question or advise would be if you are doughing in or ramping up, do you have to be careful to quickly go through the beta amylase range? Or, as I was hoping, even if you have a beta rest, there would be unconverted starches left that would be converted into long chain sugars at the alpha rest giving you a sweeter beer. Still unclear.

Jim