Author Topic: Pre-boil gravity issue  (Read 263 times)

Offline SecondRow_Sean

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Pre-boil gravity issue
« on: January 27, 2014, 03:23:14 PM »
I brewed up a quad today, completely missed my pre-boil SG/volume and am trying to figure out where I went wrong. Info is below, and I wound up hitting my targeted OG with an extended boil/addition of roughly .75lbs of DME. I'd appreciate any help you guys can give, a few of my recent brews were a bit lower than expected and I'm trying to understand what I'm doing wrong.

16lbs Belgian Pale
4lbs Maris Otter
1lb Special B

Mash ratio: 1.25qt/lb

Mash at 154f for 75minutes w/27.25qt (I hit 154f exactly on this)
Batch sparge w/15.5qt
First runnings= 1.083 (hydrometer was calibrated/verified immediately prior to reading)
Second runnings= 1.040
Pre-boil OG= 1.064 (Targeted was 1.090)
Boil volume= roughly 8.5 gallons (targeted was 7.48 gallons)

Offline dordway29

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Re: Pre-boil gravity issue
« Reply #1 on: January 27, 2014, 04:02:43 PM »
I don't think you're doing anything wrong, just low efficiency. Based on that grain bill your estimations are wrong. On average base malts give you roughly 36/ppg (points per pound per gallon).

So 20lbs * 36ppg = 720 + 34 (estimating the crystal malt) = 754
Divide that by your pre-boil volume (8.5 gallons) = 88.7
So your pre-boil gravity at 100% is 1.089 or 1.088 depending whether you round up or down
Given your measured pre-boil gravity, your efficiency was roughly 59% (According to beersmith 55%)

Offline mtnrockhopper

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Re: Pre-boil gravity issue
« Reply #2 on: January 27, 2014, 04:14:13 PM »
Have you brewed beer at this OG before? High gravity mashes tend to be less efficient anyway.

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Offline duboman

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Re: Pre-boil gravity issue
« Reply #3 on: January 27, 2014, 04:17:18 PM »
Quality of crush is always a good place to start followed by how well you doughed in. Also, how well did you stir the mash prior to first runnings and again at sparge, you really need to stir like hell to knock all the sugars loose.

Then there would be the mash pH to consider as well for proper conversion
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Offline HoosierBrew

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Re: Pre-boil gravity issue
« Reply #4 on: January 27, 2014, 04:19:37 PM »
Have you brewed beer at this OG before? High gravity mashes tend to be less efficient anyway.

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+1.  Since dordway29 calculated your efficiency @ 59% ,you could just build roughly that efficiency into your software for high OG beers. That's what I do.
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Offline SecondRow_Sean

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Re: Pre-boil gravity issue
« Reply #5 on: January 27, 2014, 04:25:59 PM »
I don't think you're doing anything wrong, just low efficiency. Based on that grain bill your estimations are wrong. On average base malts give you roughly 36/ppg (points per pound per gallon).

So 20lbs * 36ppg = 720 + 34 (estimating the crystal malt) = 754
Divide that by your pre-boil volume (8.5 gallons) = 88.7
So your pre-boil gravity at 100% is 1.089 or 1.088 depending whether you round up or down
Given your measured pre-boil gravity, your efficiency was roughly 59% (According to beersmith 55%)

Forgot to mention the 1lb of D90 in the recipe, which would bump up the post-boil OG. I just wonder why my efficiency is so low.

Have you brewed beer at this OG before? High gravity mashes tend to be less efficient anyway.

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I haven't, this was the first time I brewed something over 80ish.

Quality of crush is always a good place to start followed by how well you doughed in. Also, how well did you stir the mash prior to first runnings and again at sparge, you really need to stir like hell to knock all the sugars loose.

Then there would be the mash pH to consider as well for proper conversion

I ran the grain through the mill twice, and got what I thought was a good crush. I didn't stir prior to the first runnings, maybe that's part of the problem? Prior to the second runnings I stirred pretty well, and for the pH I followed the additions per Bru'n water but I didn't measure.

Offline morticaixavier

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Re: Pre-boil gravity issue
« Reply #6 on: January 27, 2014, 04:30:52 PM »
1:1.25 is pretty thick. I would loosen the mash up quite a bit if your doing a single infusion push it up a little, maybe 1.5 that gets you ~20 qts out of first runnings. f your kettle is big enough you can sparge with another 10 qts or so, do an extended boil to get the extra water out.

alternately you could have sparged again and done a second runnings small beer.
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