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Old 01-02-2011, 12:28 AM   #1
PolarisSnT
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Default Post boil gravity lower than pre boil

This should be impossible because the volume in the BK had decreased and all that is lost is water and the resulting solution should be higher in concentration.

At the end of my sparging I took a gravity reading (pre boil) and came up with 1.025 @150*F = 1.044 at 70*F

Boil for 1hr and chilled to 70*F and grabbed a reading before pitching the yeast. The hydrometer read 1.040.

Tried doing some research and it seems that layering in the BK could have caused me to take a reading of the higher gravity wort that was sitting on the bottom near my drain valve causing a falsely high pre-boil gravity.

Google returned this: http://www.byo.com/stories/wizard/ar...ency-mr-wizard

Thoughts?

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Old 01-02-2011, 12:38 AM   #2
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Odd, but what your research brought up for a reason sounds logical to me... I would suggest stirring the wort (next time) just before taking a sample for the reading (take it from the top if possible, or make sure you give it a good, full depth, stir to make sure it's all mixed well.

I'm just starting down the AG road (first AG brew happening tomorrow) so it's really good to read up on what others have encountered so far. Very educational, and I hope that learning from others misfortune will help me to avoid the same stumbles... Although, as long as it comes out good in the end, does it really matter?

My BK doesn't have a ball valve in it (yet) since it's just a 32 quart pot (recently purchased, and conditioned)... Once I have my pre-boil volume, I might take a hydrometer reading, just to see what it's at before being boiled.

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Old 01-02-2011, 12:44 AM   #3
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Always stir well before taking a gravity reading.

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Old 01-02-2011, 12:52 AM   #4
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You need to cool your pre-boil sample some in order to get an accurate reading. The further you are from the calibration temp the less accurate it will be after temp correction, so try to get it under 100F next time. There also could have been some layering, but I wouldn't trust your first reading either way.

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Old 01-02-2011, 12:55 AM   #5
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The hydrometer correction charts for temperatures over about 90F are notoriously inaccurate and imprecise. Always cool to below 90F, preferable all the way down to 60F to take your hydrometer reading. Other than making sure the wort was mixed well, that's likely the culprit.

EDIT: oops, what Juan said...

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Old 01-02-2011, 02:03 AM   #6
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As everyone else said ........ cool your sample down to 60-70 before taking a reading. I wait till I have all runnings in the kettle. Stir really well. Then to pull a hot sample I just grab a glass pint glass and dip it in my boil kettle to catch about 2-3 inches in the pint glass. Then I set this in some tap water in the bottom of a bucket (mini-ice bath style for my pint glass without the ice). Then once it cools down add it to your hydro test tube and take a reading.

Sounds like a pain but it only takes a few minutes and you have nothing else to do while waiting for your pot to boil ..........

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Old 01-02-2011, 05:22 AM   #7
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Thanks for the tips.

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Old 06-14-2011, 10:09 PM   #8
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Default the same thing happened to me

The same thing happened to me. my first runnings was 10 brix.
my preboil was 13.
My og was 12.
Its all whacky.

The. Beer better be good!

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Old 06-15-2011, 03:08 AM   #9
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Congratulations, you have defied physics. Suck on that, Sir Isaac Newton!

I agree with the other in that the temperature correction is just inaccurate at those temperatures.

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Old 06-15-2011, 07:58 AM   #10
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Big wish it were that simple. But I puteaxh sample in its own paper cup and placed them in the fridge to cool. Then let them sit out for an hour or so to stabilize the temp.
It may be possible that the hop particulates in the post boil are interfering with the way the light is refracted. Maybe I will run some experiments.

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