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Old 01-19-2011, 10:48 PM   #1
marnel
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Default Really strange fermentation readings

I know Refractometers are mainly for prefermentation readings but I've got some really strange results when comparing my refractometer readings against my hydrometer.

My initial readings were 16 Brix and about 1.062 SG before pitching. 4 Full days into fermentation and things appeared to have slowed down so I decided to take some readings to see where we were make sure everything was on track with no problems.

Readings today were very strange to say the least. 8 Brix and 1.030 from hydrometer. When I punch the figures into the calculators to account for alcohol I get an SG value of around 1.012 which sounds good to me.

Anybody have any ideas why the two tools could produce such contradicting results!?!

I've corrected readings for temperature with hydrometer and spun to get any air bubbles off.

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Old 01-19-2011, 10:58 PM   #2
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You don't need to correct for alcohol when taking gravity readings with a hydrometer, just temperature. 1.030 is your actual gravity reading right now, if you registered that with the hydrometer.

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Old 01-19-2011, 11:01 PM   #3
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Originally Posted by indigi View Post
You don't need to correct for alcohol when taking gravity readings with a hydrometer, just temperature. 1.030 is your actual gravity reading right now, if you registered that with the hydrometer.
I didn't correct for alcohol with my hydrometer just the refractometer reading.
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Old 01-19-2011, 11:03 PM   #4
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Quote:
Originally Posted by marnel View Post
8 Brix and 1.030 from hydrometer. When I punch the figures into the calculators to account for alcohol I get an SG value of around 1.012 which sounds good to me.
This led me to believe you'd only used your hydrometer as you didn't mention taking a reading with your refractometer at this point.

Refractometers figure out the amount of sugar in solution by measuring how light is refracted through a sample of water with sugar in it. Since alcohol has different refraction properties than water, it skews the readings by not scattering the light in the way a pure water/sugar solution would.
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Old 01-19-2011, 11:12 PM   #5
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Quote:
Originally Posted by indigi View Post
This led me to believe you'd only used your hydrometer as you didn't mention taking a reading with your refractometer at this point.

Refractometers figure out the amount of sugar in solution by measuring how light is refracted through a sample of water with sugar in it. Since alcohol has different refraction properties than water, it skews the readings by not scattering the light in the way a pure water/sugar solution would.
Might be poor choice of wording, i just figured since i was posting figures in brix and SG it would be obvious i was talking about 2 different readings one from refractometer and one from hydrometer.

I know what a refractometer measures ;-) I just find it hard to believe that the 2 figures are 20 pts off after correcting refractometer to take into account alcohol, which was the purpose of this thread.
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Old 01-20-2011, 12:19 AM   #6
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Yeah I wasn't paying full attention to your post, my apologies. Maybe there was a lot of residual CO2 in your hydrometer sample, which could skew the readings even if there aren't visible bubbles?

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Old 01-20-2011, 01:07 AM   #7
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Quote:
My initial readings were 16 Brix and about 1.062 SG before pitching. 4 Full days into fermentation and things appeared to have slowed down so I decided to take some readings to see where we were make sure everything was on track with no problems.

Readings today were very strange to say the least. 8 Brix and 1.030 from hydrometer. When I punch the figures into the calculators to account for alcohol I get an SG value of around 1.012 which sounds good to me.
Yes, that is strange. I would think after 4 days, the lower number is probably correct. Probably just means something goofy with the sample pull occurred. Did you just check it once? The easy answer is just to let beer ferment for two weeks before even thinking about doing anything ;-)

When was the last time you calibrated your refractometer?
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Old 01-20-2011, 01:19 AM   #8
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How did you take the samples? If the hydro sample was taken with a thief, and the refractor sample was a few drops from the top of the fermenter, is it possible that the density of the fermenting beer is different at different levels in the fermenter? Say the thief sample was from near the bottom, where there is still sugars remaining and the drops from the top have a higher alcohol content??

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Old 01-20-2011, 01:22 AM   #9
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Quote:
Originally Posted by marnel View Post
Might be poor choice of wording, i just figured since i was posting figures in brix and SG it would be obvious i was talking about 2 different readings one from refractometer and one from hydrometer.

I know what a refractometer measures ;-) I just find it hard to believe that the 2 figures are 20 pts off after correcting refractometer to take into account alcohol, which was the purpose of this thread.
Well, that's the difference between a refractometer and a hydrometer, once alcohol is in the mix.

Remember that refractometers don't account for alcohol, so it "skews" the reading badly.

The easy fix is to use a refractometer pre-fermentation and a hydrometer post- fermentation.
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