Mash Enzymes and Amylase Activity Question

[citizensnips]

Hoping to get an answer for a question regarding starch breakdown in the mash.

Basically my question is this.....I'll try and simplify it so it doesn't become convoluted.

It's my understanding that for beta-amylase to be active in the mash (primarily active between 60-65 C), it requires the breakdown or exposure of starch molecules from alpha-amylase (primarily active between 65-73).
Here's what I don't quite get, if one were to mash at say 61 degrees C where alpha-amylase is pretty much inactive, what would be the resulting fermentability of the mash?

From memory I can recall mashing low, perhaps 62ish and although requiring a longer rest time it has resulted in a very fermentable wort. So in other words how can you get such good fermentability without the initial breakdown of starch from a-amlyase when it's required in order for b-amylase to come in and get the job done?

Hopefully that makes somewhat sense without getting into it too much.

Cheers for answers in advance

 

[MHB]

Answer is that there is a fair bit more Alpha activity cooler than you think, the "activation" temperature for Alpha is around 60oC, the peak is 72oC and this gives a fair idea of the relative rate of activity as a function of temperature (comp Kunze I think)

The far right of the graph is where Alpha is deactivated (denatured) and would be around 80oC.
A long (60m+) mash at 61oC would result in very dry beer.
Mark

 

[citizensnips]

Thanks Mark.

I assumed a-amylase must be more active than suggested in these lower temperatures, otherwise it just plain didn't make sense. I guess that explains why you need the longer rest at lower temps, to allow for that slowed alpha activity to take place?

It's funny how many recognised textbooks provide varying responses to ideal temperatures for certain enzymes. It still seems to be largely debatable (to a certain extent).

 

[MHB]

It's worth remembering that all the enzymes will work at ambient temperatures, they aren't there for brewers but to supply soluble nutrients to a little growing barley plant. They just work too slowly to suit our purposes.
If you look at the graph I posted, from the dotted line (peak) to where its denatured is about 20oC, if you proportion the same amount to the left of the line, you are about half way from minimal to peak activity, lots of ends being provided for Beta-Amylase to chew on.

I don't think there is much debate about the temperatures at which enzymes work, there was in older textbooks, but these days most people are in agreement (give or take 1oC or so).
The exception being some of the protease activity, there are 4 major proteases that peak around 55oC, but they don't all behave the same.
Mark

PS
Very fair question, if you want to know more have a look at Braukaiser, he covers enzymes pretty thoroughly and has recently published the results of an experiment on wort fermentability and temperature - worth reading.
M

 

[citizensnips]

Right. So according to that graph, a-amylase is working considerably lower than 60 degrees, just at a very slow rate. Either way that makes a lot more sense to me now. Nonetheless in none of my readings has it mentioned alpha-amylase being even marginally active or activated at 60 degrees. Knowing that you can logically piece together how a mash rest of 61 results in a dry beer, without knowing that your left to wonder how beta-amylase can gain access to enough reducing ends without the work of a-amylase.

Either way much appreciate the responses and glad that it now makes sense.

The learning continues

Cheers