Low PM Efficiencies

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LoadedFront

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Just brewed my first PM using DB's stovetop method not too long ago. I did have some problems maintaining temperature, and my patience got the best of me at a couple points, so I didn't expect great results, but I am curious as to what the common causes of low efficiency are.

The recipe was for a Chocolate Oatmeal Stout and the grain bill was:
1 lb. 6-row
1.5 lb. oatmeal
0.5 lb. black
0.5 lb. roasted barley
0.75 lb. crystal - 40L
0.75 lb. chocolate

The recipe also used 6.5 lbs. of DME (mostly light, I think a pound of dark; don't have my notes in front of me).

In Beer Smith, my efficiency came out to something like 40%. My temps tended to run a bit hot (160-165 rather than 155), and I may have been a bit shy on water. Any thoughts/input appreciated.
 
In Beer Smith, my efficiency came out to something like 40%. My temps tended to run a bit hot (160-165 rather than 155), and I may have been a bit shy on water. Any thoughts/input appreciated.

That would explain the poor efficiency. You want to have 1.25-2 quarts per pound of grain. Temperatures are also crucial. At over 160, you could very quickly denature the enzymes.

The other thing to keep in mind is that you want the same amount of base grain as other grains, to ensure conversion. With only 1 pound of base grain, and all the others specialty grains, you wouldn't be able to convert all of the sugars in the oats. With 4 pounds of specialty grains, you'd need 4 pounds of base malt to ensure good conversion.

The too-high temperature, combined with inadequate enzymes, would be a big factor.
 
Yooper-

Thank you for your reply. So, I more or less just ended up with extract + specialty grain on this batch, then...

One follow up to your post:

I thought that the specialty grains wouldn't mash; they were just for steeping. My assumption was that that was why there was so little base grain since only the oats would mash, and the 6-row has the highest diastatic power of the base grains.

Thanks again for your time.
 

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