Author Topic: PPG from extract doesn't seem to be a constant  (Read 2290 times)

Offline GigaFemto

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PPG from extract doesn't seem to be a constant
« on: December 06, 2016, 11:24:09 AM »
I have been confused by the gravity calculations for extract in BS 2.3.7. It seems that the points per pound per gallon changes depending on trub losses, which doesn't make sense to me. I made 2 simple example recipes to demonstrate, which I have exported and attached. They both use 4 lbs of base malt and 4 lbs of DME which is listed as having a potential of 1.045 (i.e. 45 ppg).

Recipe 1:
No trub loss, no kettle top-up. BH efficiency = Mash efficiency = 77%
Post-mash gravity = 1.036, Pre-Boil volume = 3.14 gallons, Pre-Boil Gravity = 1.093
The diiference between post-mash and pre-boil gravities is from the DME
The contribution from the DME is (93-36)*3.14/4 = 44.7 ppg, close enough to 45

Recipe 2:
1 gallon trub loss, no kettle top-up. BH efficiency lowered to 64.2% to give mash efficiency of 77% again
Post-mash gravity = 1.026, Pre-Boil volume = 4.4 gallons, Pre-Boil Gravity = 1.075
The contribution from the DME is (75-26)*4.4/4 = 53.9, much higher than before

I understand that the volumes will  change and the boil-off amount need to be adjusted, etc. but this is all pre-boil and the ppg shouldn't change.
What am I missing here?

 ???

Offline durrettd

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Re: PPG from extract doesn't seem to be a constant
« Reply #1 on: December 06, 2016, 04:02:16 PM »
If I'm understanding your data, I think I see the problem:

Brewhouse efficiency is the points coming out of your system divided by the points going into your system, expressed as a percentage. When you leave trub behind, you are also leaving wort behind which means you are losing the sugars in that wort. You have left "points" behind. Those points went in but left the system when you poured them down the drain. They didn't exit the system as wort into your brew kettle.

Let me know if I'm answering the right question.

Offline GigaFemto

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Re: PPG from extract doesn't seem to be a constant
« Reply #2 on: December 06, 2016, 04:36:34 PM »
Thanks for the attempt, but that is not the issue. I understand  that leaving wort/trub behind in the kettle will reduce the Brewhouse efficiency. In recipe 2 I lowered the BH efficiciency to get the same mash efficiency (77%) that I usually get, and the same as in the recipe with no trub loss. The problem is happening pre-boil, before anything gets left behind. The boil volume increases to compensate for the fact that some will be left behind later, but I have taken out that difference in volume when calculating points per pound per gallon. That should be a characteristic of the extract that doesn't change. When going from post-mash gravity to pre-boil gravity the only thing that happens (as far as I know) is that the extract is added (you could add kettle top up water, which would affect volumes and gravity, but I had that zero in both of these recipes).

 

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