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Old 01-10-2011, 05:34 PM   #1
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Default Gravity Difference pre vs. post chilling.

Hey everyone, anyone run into this phenomena?:

I'll take my refractometer reading just after creating a whirlpool and letting it settle, while the wort is hot in the boil kettle, and I'll get say, a gravity of 23. I send it through the plate chiller and the gravity is 17.5.

Is this a plate chiller issue ie. we're taking particles out of the wort, is it a cold-break issue?

We've tested it against a hydrometer sample that has been taken out of the hot side and chilled in an ice bath, vs a hydrometer sample that has come out of the plate chiller and get the same results as the refractometer readings.

Thanks

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Old 01-10-2011, 09:03 PM   #2
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Even if the refractometer is ATC you still need to let it sit for a few minutes at room temperature before checking the gravity. I'm guessing this is the issue.

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Old 01-10-2011, 09:06 PM   #3
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Leak in the plate chiller that is diluting your wort with chill water?

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Old 01-10-2011, 09:22 PM   #4
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Originally Posted by AZ_IPA View Post
Leak in the plate chiller that is diluting your wort with chill water?
That would quite a leak to go from 1.096 to 1.070.

I vote - (1) not properly cooling the sample to room temperature or (2) selecting a turbid sample. Selecting a sample with visible hot break can cause off readings.
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Old 01-11-2011, 12:04 AM   #5
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That would quite a leak to go from 1.096 to 1.070.

I vote - (1) not properly cooling the sample to room temperature or (2) selecting a turbid sample. Selecting a sample with visible hot break can cause off readings.
the numbers I used were just random numbers I chose to illustrate better what I was saying-but yeah it does make sense what you're saying about hot break.

I do see floaties in the hot sample, i try to avoid them to no avail, they're pretty much homogeneously spread out throughout the boil kettle-but they don't make it to the fermenter.

I was leaning towards this too-thanks.

I'm still sort of baffled as far as hitting similar efficiency marks with my system-I get really consistent 80 percent efficiency with about half of my recipes, but not so much with others. I understand with a big grain bill I'm going to get lower efficiency unless I decrease the water to grain ratio in the mash, or sparge longer, and boil longer to increase the amount of extract yield, so it doesn't really bother me that with different brews my efficiency is slightly off.

It just bugs me that post-sparge I get one number, before boiling,and so I scale down the volume to see what the gravity is going to be using beersmith. Then the gravity is way more than what I think it would be after boiling(flawed logic perhaps using apparent efficiency pre boil to estimate it post boil?). Then, post-chill, I get numbers lower than what I think it should be.

The erratic gravities are frustrating with new recipes, in estimating what the OG we're going to hit is. Once we get a certain result however, it repeats with the subsequent brews of the same recipe.

Brewing = trial and error, but really fun trial and error.
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Old 01-11-2011, 12:07 AM   #6
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Even if the refractometer is ATC you still need to let it sit for a few minutes at room temperature before checking the gravity. I'm guessing this is the issue.
I thought of this too, and waited to check the reading, no dice. Thanks though -I wish that was the issue!
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Old 01-11-2011, 12:29 AM   #7
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Theoretically the floaties should not skew the reading, but just make the blue/white line hazy since the refractometer is supposed to measure dissolved sugar using refracted light. Chunks don't refract light AFAIK. However, since the protein that will become cold break material is still dissolved in the wort when it's still hot, maybe it bends the light some too throwing the reading off. That doesn't seem to make sense though since you got the same results as the refractometer with a chilled down hydrometer reading... in that case the cold break material should have coagulated in the sample jar and wouldn't be dissolved anymore either. And when the few drops hit the glass on the refractometer it should have a mini-cold break right? Interesting for sure.

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Old 01-11-2011, 12:47 AM   #8
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Theoretically the floaties should not skew the reading, but just make the blue/white line hazy since the refractometer is supposed to measure dissolved sugar using refracted light. Chunks don't refract light AFAIK. However, since the protein that will become cold break material is still dissolved in the wort when it's still hot, maybe it bends the light some too throwing the reading off. That doesn't seem to make sense though since you got the same results as the refractometer with a chilled down hydrometer reading... in that case the cold break material should have coagulated in the sample jar and wouldn't be dissolved anymore either. And when the few drops hit the glass on the refractometer it should have a mini-cold break right? Interesting for sure.
Next time I brew I'll make a thread about it, I don't have exact numbers to give that would make this a more adequate discussion. I'll take pictures so we can examine it further. I'm interested too, maybe the numbers are off in my head. I'll have to treat it like a legit experiment with legit observations.
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