question about discrepancy between my hydrometer and refractomer

Just bought a refractometer. Making some flower based wine and so added 2.25 lbs of sugar to make a gallon of must. By calculation this should be close to 1.090. Tested the must with my hydrometer - 1.089. Took a sample of the must and placed it on the screen - reading was 1.068. I had calibrated the refractometer with distilled H2O.. Last week I started a SMaSH recipe and used the refractomer to give me an idea of how efficient my system was and I got a shock when what should have been a wort with a gravity of 1.061 was about 1.045 on this refractometer. This is a simple device. Can it possibly be so inaccurate? What might I be doing to produce such bizarre results?

A refractometer is a device that measures the refraction of light passing through a solution. A hydrometer is a device that measures the density of a solution. Neither measures the concentration of sugar in a solution yet both are calibrated in Bx which is the w/w concentration of sucrose in solution. Now if the solution you are measuring is a sucrose solution both instruments read correctly. If the solution is like (a very vague word) a sucrose solution both read approximately correctly. If the solution's behaviour with respect to refractive index is not like that of a sucrose solution then the refractometer will read in error. If the solutions behaviour with respect to density is not like that of a sucrose solution then the hydrometer will read in error. Beer worts are not sucrose solutions nor are wine musts but the sugar spectrum in beer is such that it behaves very like sucrose and thus hyrometers are good for measurement of wort. Musts contain a much higher percentage of sucrose and are thus suited for measurement with hyrdrometer or refractometer. Worts are not and it isn't unusual to see a discrepancy of a couple of Bx between refractometer and hydrometer when measuring wort. But you are seeing a discrepancy of 4 Bx on wort which is way large and almost 5 on a sucrose solution so the conclusion is that your refractometer is broken.

If you can make measurements add 68.1 g sucrose to a half liter of distilled water to make a 12 Bx solution and measure that. If you refractometer doesn't read close to 12 with that, toss it.

ajdelange said:

If you can make measurements add 68.1 g sucrose to a half liter of distilled water to make a 12 Bx solution and measure that. If you refractometer doesn't read close to 12 with that, toss it.

Click to expand...

The sugar I added to create the must was sucrose... But I really like your idea of creating a 68.1 g sucrose solution in .5 L of water. Thanks.

bernardsmith said:

The sugar I added to create the must was sucrose...

Click to expand...

I understood that and given that I assume the dandelions (or whatever) don't contribute much 'extract' the refractometer ought to read correctly. The fact that it didn't makes me suspicious of it.

Don't forget to consider temperatures for the readings, especially the hydrometer.

-BD

BrunDog said:

Don't forget to consider temperatures for the readings, especially the hydrometer.

-BD

Click to expand...

agreed

Also, make sure you verified the calibration of your hydrometer! I recently had to return one that was off by 0.005, and go back to re-adjust all of my gravity readings for 5 batches

The hydrometer COULD be off except that by calculation the reading ought to have been 1.090 (give or take a point or so) and my hydrometer was right on that mark... The refractometer is ATC which ought to mean that it does not need recalibrated as the ambient temperature changes...and anyway, you make wine indoors (no heating because no brewing) and the must was at room temperature....

ATC in a refractometer is not like ATC in a pH meter. It tries to compensate for the changes in refractive index of sucrose solutions which it does by rotating the prism or moving the scale - a mechanical kluge. ATC refractometers must be used at the calibration temperature unless, of course, you are measuring sucrose solutions.

Follow-up. I wrote the company that sold me the refractometer and they agreed to send me a replacement (and gave me the postage to return the defective instrument). The replacement was already calibrated and when I tested it against a reading from my hydrometer it was close enough to be good enough. I just want to give the company a shout out for really good customer service - The seller is Opticalfactory on ebay

Sorry to bump an old thread but I was just looking at their (opticalfactory) "World's most Accurate" refractometer on Ebay. Don't know if that's the one you have but I was wondering if you were still happy with yours. Thanks for any info you can give me.

HomebrewHandicapper said:

Sorry to bump an old thread but I was just looking at their (opticalfactory) "World's most Accurate" refractometer on Ebay. Don't know if that's the one you have but I was wondering if you were still happy with yours. Thanks for any info you can give me.

Click to expand...

Just found your post - Short answer is yes, still very pleased with the hydrometer. I just started a batch of something like a braggot last night (I am using only specialty grains - not base malts) and the SG indicated by my refractometer was 1.080 which was precisely the same as the reading my hydrometer gave and pretty darn close to the reading I expected from the calculations I did given the amount of sugars from the honey and the volume of liquid..

Thanks. Glad to hear you're still happy with it, cause it made it to my Christmas wish list. 😃