Effect of Mash Temperature on Extraction Efficiency

For context, I do 2.5-gallon stovetop BIAB AG brews.

Two brews ago, my mash temp got away from me (I didn't allow for continued heating from the electric coils on my stove after turning the burner off) and I mashed at 158 F. My extraction efficiency was 77%. With yesterday's brew, I paid attention and mashed at 154 F. That brew had an efficiency of 85%.

From Palmer's book, I recall that beta amylase is denatured at higher temperatures and I was wondering if this might explain my lower efficiency in the earlier brew and the higher efficiency in the later brew.

Everything else was pretty much the same (90-minute mash, squeeze the heck out of the bag) except that the earlier brew had a mashout at 172 F and the later brew at 170 F. For the efficiency calculations, the max sugars were based on actual grain weights and gravities, not averages, and the actual sugars extracted were based on the start of boil volume and gravity.

Thoughts?

I don't see how the temperature could affect efficiency- I mean, converted is converted. I do get higher efficiency when I do decoctions, but that isn't really the same as a 4 degree difference in mash temperature. For one enzymes thing, don't denature imediately. The only thing rising temps do is to increase the rate of denaturation. The temperature would affect fermentability of the wort, but not efficiency.

I'd look more to the grainbill and the crush. If the grain was crushed finer, that could explain the higher efficiency. For the grainbill, maybe the mash pH was a bit too high in the one with the lower efficiency.

Hmm. The first grainbill was crushed by a mail order shop. (I requested a double crush, but don't know if they did.) The second one was double-crushed by me at the LHBS.

I used the same (tap) water each time. The first time, I checked the pH of the water and have it written down at home. Neither time did I check the pH of the mash itself.

As far as the enzymes, I was wondering if the beta amylase didn't do much because of the higher temperature the first time, thus decreasing the amount of conversion. I think you are saying that the conversion still did occur, just that the conversion products would have been a bit different due to the different temperatures.

So, maybe the crush explains it.

smyrnaquince said:

Hmm. The first grainbill was crushed by a mail order shop. (I requested a double crush, but don't know if they did.) The second one was double-crushed by me at the LHBS.

I used the same (tap) water each time. The first time, I checked the pH of the water and have it written down at home. Neither time did I check the pH of the mash itself.

As far as the enzymes, I was wondering if the beta amylase didn't do much because of the higher temperature the first time, thus decreasing the amount of conversion. I think you are saying that the conversion still did occur, just that the conversion products would have been a bit different due to the different temperatures.

So, maybe the crush explains it.

Click to expand...

Yes, it could very well be the crush. But check the mash pH each brew to make sure it's in range.