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Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > Question on preboil and postboil OG
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Old 04-20-2014, 07:22 PM   #1
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Default Question on preboil and postboil OG

So I brewed a pale yesterday and I had something new happen with my OG. Beersmith gave me a Est preboil OG of 1.039 and I measured 1.041 with my refrac which I calibrated with distilled at the beginning of the day. I figured close enough and went on with my boil. Beersmith gave me an Est. OG of 1.051 but it only came out to 1.045 on the refract. I figured no way, so I took a hydrometer reading and got the same reading. I also checked the hydro with distilled and it checked fine. Any ideas how or why I missed my OG by so much. Normally if I'm way off on my preboil I will adjust with DME and the OG falls right in line after the boil. I don't understand how the OG only went up 4 pts after a 60 min boil.

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Old 04-20-2014, 07:30 PM   #2
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Sounds like you may not have evaporated enough water off during the boil... Did you still hit your target volume?

Edit: Also what temperatures were you making your readings at? If you read at a temp other than 20°C you will need to make an adjustment.

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Old 04-20-2014, 07:41 PM   #3
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I have been trying to dial in my boil rate(Got a new Blichmann burner) but I was only slightly higher in volume than usual. I shoot for 6 gal after the boil and I had about 6.25. I took the refractometer readings as I normally do. I grab a little wort with my spoon, blow on it and let it cool for 30 secs or so and the put it on the ATC refract and take a reading. The hydro reading I took was after chilling to 68. Would the extra .25 gallons be enough to through the OG off 6pts?

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Old 04-21-2014, 01:08 AM   #4
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No, the extra quart should only drop it by about 2 points at that volume. From your initial numbers it sounds like you only boiled off about two quarts... Maybe you had less pre-boil volume than you thought? Did you measure your pre-boil volume?

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Old 04-21-2014, 03:14 AM   #5
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Pre-boil volume was 7.5 gallons. Normally I have 1.5 gal/hr boil off. I must have not been boiling as hard as usual.

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Old 04-21-2014, 03:17 AM   #6
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The only answer I can think of is my initial pre-boil reading was wrong. Maybe I didn't mix the kettle up well enough and got a false reading?

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Old 04-21-2014, 03:27 AM   #7
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False readings happen all the time, you will probably be okay. Did you remeasure your final cooled volume to see how much you actually have left? I got a lesson about propane tanks a few days ago, I had my regulator set at a particular place to have decent boil times, but not boil overs. The tank was getting low, the flame was going down, I reset the regulator, I then changed to a full tank w/o resetting the regulator, and I went from 7.5 to 4.5 gallons before it dawned on me what my error was.

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Old 04-21-2014, 03:35 PM   #8
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My final volume was about a qt more than expected but I always drain off 5.5 gallons into the fermenter. I figure the batch will turn out okay but the ABV will be lower than expected of course. I only worry about the hop balance with the lower gravity affecting the flavor.

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Old 04-21-2014, 05:07 PM   #9
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I don't think you have anything to worry about. You'll get a couple more IBU's from your hops with the lower gravity but it shouldn't be anything noticeable. To find the difference, adjust your efficiency in Beersmith down until it estimates your OG to be 1.045 without changing anything else in the recipe. It will show you then new IBU estimate for that gravity.

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Old 04-21-2014, 07:17 PM   #10
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Thanks for the advice everyone!

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