Measuring high gravity worts

[kerneldustjacket]

@tschmidlin

Get yourself a small graduated cylinder, then dilute the wort with an equal amount of water.  Multiply the refractometer reading by 2, and bob’s your uncle.  It will be cheaper than buying a high gravity refractometer, $7.50 from morebeer.

http://morebeer.com/view_product/6540//Graduated_Cylinder_-_10mL

@kaiser

I believe the dilution has to be done by weight. E.g you need to mix 50g of wort with 50g of water. I’m not completely sure for SG. But I’m sure for Plato since that is a weight based extract measure.

Kai

I did a quick experiment to see what happened when both methods where used; i.e., one where equal volumes of water and a sugar solution are combined and measured, and the other where equal weights of water and a sugar solution are combined and measured. The refractometer measures in Brix, which is defined as % of sucrose by weight in a solution; where 1 gram of sucrose is in a 100 gram solution, you have 1 Brix. Note however that the actual measurement is made using light refraction, and the reading in brix is extrapolated from the result of that light refraction.

1. a 10 brix solution was made by weighing 10 grams of table sugar on a scale that weighs to a tenth of a gram, and topping it off with water to make 100 grams total weight (Note: prior to the experiment, I made two solutions: one where 10 grams of sugar was combined with 100 grams of water – making 110 grams total weight, and the other where 10 grams of sugar had enough water added to make a 100 gram total weight solution; the 100 gram total weight solution gave the reading of 10.0, as expected)

2. This sample gave a reading of 10.0 on my refractometer (a “zero” calibration was made to the refractometer just prior); as a cross check, I tested the sample with my hydrometer: 1.040

3. 20 grams of sugar solution was combined with 20 grams of water; this gave a reading of 4.8 brix

4. 15 mL of sugar solution was combined with 15 mL of water; this gave a reading of 5.0 brix

5. I alternated the two samples, taking a total of four readings per sample; the results did not vary. I also carefully cleaned the refractometer between all readings

Now I grant that these results vary by a small amount, likely due to the sample solution being only 10 brix; perhaps a second run with a 20 or even 40 brix sample might better show any variance. But, the equal volumes method seemed to work best for diluting a sample to read half the actual brix of the solution.

I suspect that where refractometers are concerned, dilution of an equal amount of water does approximate the sugar content by half. I think this is because refractometers measure a refraction of light caused by the absolute volume of sucrose present, rather than its weight.
Also note: refractometers ONLY measure sucrose…higher gravity worts MAY read incorrectly, depending on the nature of the wort sugars that are present.

Just my $0.02 worth.