Problems With Refractometer Readings

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ampy

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Hi all
I recently bought a cheapish refractomer on eBay, and I am getting conflicting SG readings against my trusty Coopers Hydro which I have been using for years.

Here they are
photo.jpg


I just took a reading from a batch I just put into the fermentor and got a reading of 1051 with my hydrometer and a reading of 1046 with the refrac. Should I just turf the rafrac and get another one, or can I re-calibrate it to the hydro ie, hydro sample 1051, adjust refrac sample to 1051? Although I dont think its that simple.
Any help from others using refractometers would be helpful.
Cheers
ampy
 

Greg Lawrence

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Pretty sure that fermenting beer puts the reading out.
I just use my refractometer for the brewing process. After the yeast is pitched, use the hydrometer.

Greg
 

mxd

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if we assume you weren't "fermenting" at the time then I believe there is a way to calibrate, is there a screw on top ?

If you were fermenting then you need to "convert" your refractometer reading (I do this in beersmith)
 

brocky_555

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test some water with it to see if they both read 1.000 but the water for the hydrometer must be 20 degrees celcius or what ever temp the hydrometer is calibrated to
 

matr

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I've had exactly the same problem. Low readings using the refrac. But it reads 1.000 with water.

Hence why the refrac doesn't get used. Would like an answer too.

Cheers, Mat.
 

ampy

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if we assume you weren't "fermenting" at the time then I believe there is a way to calibrate, is there a screw on top ?

If you were fermenting then you need to "convert" your refractometer reading (I do this in beersmith)


OG reading taken just after yeast was pitched so no fermentation yet. There is a calibration screw on top, I set it to 1051 to match the hydro sample, but now when I take a water sample it reads 1005, just want to know whether or not to get another one, as I am trying to work out my efficiency on my new brew rig.
 

mxd

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OG reading taken just after yeast was pitched so no fermentation yet. There is a calibration screw on top, I set it to 1051 to match the hydro sample, but now when I take a water sample it reads 1005, just want to know whether or not to get another one, as I am trying to work out my efficiency on my new brew rig.

but how do we know which one is right ? What temp is the wort, what temp is the calibratin for etc.. ?
 

ampy

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test some water with it to see if they both read 1.000 but the water for the hydrometer must be 20 degrees celcius or what ever temp the hydrometer is calibrated to
was originally calibrated using water to 1000
hydro reads 1000 with water @ 20 deg
 

Bizier

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When did you last calibrate the refrac?

I would also like to know why my last brew read 1.097 on the refrac, calibrating multiple times that day due to large ambient temperature shifts, and it measured 1.111 in the hydrometer at time of pitching. It seemed accurate enough on the lower gravities, but was significantly out at the top of the range.
 

ampy

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When did you last calibrate the refrac?

I would also like to know why my last brew read 1.097 on the refrac, calibrating multiple times that day due to large ambient temperature shifts, and it measured 1.111 in the hydrometer at time of pitching. It seemed accurate enough on the lower gravities, but was significantly out at the top of the range.

I usually check it before each brew session, which I did yesterday before taking my first reading, according to the refrac i wasn't hitting my pre boil sg target. But when I tested it today with the hydro I got 2 points above my target OG.
 

Rudy

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Refractometers measure sucrose, not maltose, so there is a correction factor for this. If you have a reading in Brix use your software to convert to SG and see if the reading is closer to your hydrometer
 

ampy

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Refractometers measure sucrose, not maltose, so there is a correction factor for this. If you have a reading in Brix use your software to convert to SG and see if the reading is closer to your hydrometer

Re calibrated refrac to 1000 using water, only tap water mind you, i dont have distilled water.
Took a sample 12.4 brix
converted to sg in beersmith (unfermented wort gravity) = 1.049 alot closer

The resolution on the brix side is in incriments of 2 brix so my eye could be out.

Thanks for ya help rudy
 

MHB

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If you really want to test your refractometer it's easy enough to make a calibration solution; 100g of sugar dissolved in water to make 1 Litre is 10oP or 1.040 (well so close it doesn't matter).
Remember that your calibration solution is only as good as your measurement of both the mass of sugar and the total volume, if you don't have accurate enough equipment ask around your club or friends.
I got the shits with one cheap Refrack that was giving me the same problem as mentioned above (accurate at low gravities and progressively worst at higher ones), the scale was wrong, someone had flubbed the conversion from Brix to SG and the Brix scale was fine.
MHB

Oh Brix and Plato (oP) are basically interchangeable from either to SG ≈ (4*oP)/1000 + 1
125g sugar + water to make 1 litre is 12.5% w/v or 12.5oP or 12.5 Brix or 1.050 SG all the same.

M
 

ampy

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If you really want to test your refractometer it's easy enough to make a calibration solution; 100g of sugar dissolved in water to make 1 Litre is 10oP or 1.040 (well so close it doesn't matter).
Remember that your calibration solution is only as good as your measurement of both the mass of sugar and the total volume, if you don't have accurate enough equipment ask around your club or friends.
I got the shits with one cheap Refrack that was giving me the same problem as mentioned above (accurate at low gravities and progressively worst at higher ones), the scale was wrong, someone had flubbed the conversion from Brix to SG and the Brix scale was fine.
MHB

Oh Brix and Plato (oP) are basically interchangeable from either to SG ≈ (4*oP)/1000 + 1
125g sugar + water to make 1 litre is 12.5% w/v or 12.5oP or 12.5 Brix or 1.050 SG all the same.

M

Thanks MHB will also try the calibration solution.
Cheers
ampy
 

cubbie

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From Promash

Brix Correction Factor:


A Brix refractometer reading is based on the known values for percentage sucrose solutions. However, wort contains many substances other than sucrose, and many of them have different refractive indices than sucrose. For this reason, it is necessary to use a correction factor to convert from a Brix refractometer reading of raw wort to the actual gravity of the wort. The literature suggests this factor is between 1.02 and 1.06, with 1.04 often used as a default value.

To determine your own, brewery-specific Brix correction factor:

(1) Take a hydrometer sample of unfermented wort.

(2) Measure its gravity with the most accurate, calibrated hydrometer you have. Do not forget to do the temperature offset calculations. (Alternative: use a digital density meter or pycnometer -- the idea here is to get a very accurate measurement of the actual SG / Plato of the sample.)

(3) Convert this value to Plato if you measured in SG.

(4) Using a zeroed refractometer, take the refractometer reading of the same sample.

(5) Convert this value to Brix if measured in RI or Zeiss units.

(6) Brix correction factor = Refractometer reading (in Brix) / Measured Gravity (in Plato) E.g., Refractometer reading = 13.1 Brix Measured gravity = 12.7 Plato Brix Correction factor = 1.0315

(7) Do this with several different samples and average the results. The literature suggests that the value should be consistent within a particular brewhouse.

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