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Using an Automobile Battery Refractometer for Making Wine and Beer
Old 11-14-2017, 08:09 AM
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Default Using an Automobile Battery Refractometer for Making Wine and Beer

Auto Refractometer "Calibration" with Specific Gravity

I went looking for info on using a refractometer designed for estimating the freezing protection of automotive anti-freeze and effectiveness of battery electrolyte, to estimate the original specific gravity of starting fermentation liquids. I didn't find much. I did find one person from a thread in '06 http://www.homebrewtalk.com/showthread.php?t=101163 (see post #4) using an automotive refractometer, but he didn't provide his "decoding ring".

The specific model of refractometer I have is "7181 AO DUO-CHEK" made by American Optical Corportation, located in Buffalo N.Y. (At least when this one was made.)

I started with 8 oz of water (236.6ml) to which I added level tablespoons (12.14g) of granulated table sugar. The water was a little cooler than room temperature at 69F. I first checked the hygrometer and refractometer with de-ionized water (DI). I added one tablespoon of suger then measured specific gravity (SG) using the hygrometer, and then checked the "temperature" reading of the solution using the refractometer. I added a total of three tablespoons or 36.4g of sugar. Initial readings with DI water were 1.000 SG and "+32" degrees Fahrenheit on the refractometer. (That means tat my "anti-freeze" would freeze at 32 degrees F, which is correct for pure water.) Each following reading taken after the addition of a tablespoon of sugar can be seen in the image of the spreadsheet below in cells E5-8 and F5-8 respectively:

A simple linear regression was calculated for the relationship of the hygrometer SG readings to the refractometer's "temperature" reading. While I was careful with measurements of water and sugar, the readings of SG and Temp were "eye-balled". Still, the fit of the model to the data is good with the square of the residuals being 0.9879. The values of SG predicted by the model are in cells G5-8 and can be compared to measured values in cells E5-8.

I have no hobby horse to ride here. Just presenting a set of data with some analysis for those that might be interested in using a tool they have in hand, like I was. Use my 'decoding ring' as 'you' see fit.

Then you will know the truth, and the truth will set you free. John 8:32

"We make men without chests and expect of them virtue and enterprise. We laugh at honor and are shocked to find traitors in our midst. We castrate and bid the geldings be fruitful." ~ C.S. Lewis.

Do not confuse technical skill for wisdom and do not confuse strength for skill. Paul Skvorc
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