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Old 12-14-2008, 10:29 PM   #1
physfarm
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Default Partial Mash Calculations and Qbrew

My calculations with qbrew don't seem to match pre and post boil. I've had this problem with both an Oatmeal Stout and a partial grain version of Edworts Haus Pale Ale.

For the Pale Ale, I took a gravity reading after sparging and it was 1.047 (after cooling and temperature adjusting) in about 4.8 gallons. I entered this in qbrew and adjusted to my efficiency to match and came up with 82 percent. I used this to decide how much extra pale dry malt extract to add. I added 1 lb. Before pitching yeast I took another Grain gravity reading and had 1.047 for 5.4 gallons. To make this match up in qbrew I had to adjust my efficiency for the mash down to 75 percent.

Obviously my efficiency didn't change during the boiling process, so either I am making a mistake or I am misusing qbrew some how. Well either way I am making a mistake . Anybody have an idea where I am messing up?

Thanks in advance.

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Old 12-14-2008, 11:19 PM   #2
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I highly recommend calculating your efficiency by hand. For each grain, just take the amount used and multiply by it's respective potential extract. Add all these values together. Now, take your actual gravity points (which is (1 - G) * 1000), where G is the gravity and multiply by the volume of whatever your measuring the gravity of (boil, fermenter, etc). Then take that number and divide by the first number you calculated, multiply by 100 and you'll have your efficiency for whatever step. For brew house efficiency, it's simply SG going into the fermenter after adding top off water divided by potential extract. Hope that helps.

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Old 12-15-2008, 01:20 AM   #3
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Thanks for the response nukebrewer. I took your advice checked the calculations by hand and (if I'm right) they agree with qbrew. Except I changed the potential of vienna to 34 instead of 35. Heres what I looked at:

I mashed
5 lb of 2-row at 37 ppg = 185
2 lb of Vienna at 34 ppg = 68
.5 lb of Crystal 10L at 35 ppg = 17.5
total = 270.5 gravity points

The measured gravity was 1.046 at 70F which is 1.047 corrected which gives 47*4.8 gallons = 225.6 points.

So the efficiency would be (225.6/270.5)*100 = 83.4 %

Towards the end of the boil I added 1 lb of DME and I topped off with enough water in fermenter to have 4.5 Imperial gallons or 5.4 gallons. I then took another gravity reading of 1.046 at 70F or 1.047 corrected. Which would give me 47*5.4 gallons=253.8 gravity points.

The issue I have is if my gravity readings were correct both times, then I only gained 28.2 gravity points out of 1 lb of DME where I should have gained 45.

A couple things that I think it could be: It is possible I did not add 1 lb of DME, but I would have to be off by 6 ounces to account for the differenceand I am sure my digital scale is not that far off. It is also possible that I did not estimate one of the volumes correctly. The level was right at the 4.5 imperial gallon mark in my fermenter, so that leaves the volume in the brew kettle. Its a 5 gallon brew kettle marked every gallon and was almost completely full (I had to move some over to another bot to boil). So, I would think my estimate would be close enough to not account for that much error.

Sorry for the lengthy explanation. It could be a combination of the things I just mentioned, but I am just wondering if there is something else that I am missing since this as happened twice. Anyone see another possibility that I am overlooking? Am I making a mistake with the calculations? I should get 45 points out of a pound of dry malt extract, right?

Thanks again.

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Old 12-15-2008, 03:03 AM   #4
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Did you use whole leaf hops? If so, did you filter them out? When I brewed my Neck Snapper IIPA, the hops absorbed so much wort I wasn't even in style by the time I topped off to 5 gallons, all because I filtered out the hops.

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Old 12-15-2008, 03:36 PM   #5
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I used pellet hops and everything that was in the brew pot went into the fermenter.

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