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Brix and Hydrometer Discrepencies
I've been noticing, now that I have been using my brix more, that its reading the same as my hydrometer at higher gravities i.e start and end of the boil, but when I check for the completion of fermentation, the brix is reading different than the hydrometer. The latest example is that of a czech pils that is nearing 3 weeks in primary. Last weekend I checked it with the hydrometer, mainly because I wanted a taste, but anyway the reading then was 1.020. Yesterday, so 9 days later, I checked with the brix, it read 7.9 = 1.031, obviously gravity doesn't go up so imagine my surprise. Checking with the hydrometer revealed 1.016. Both instruments measure 0 with tap water, they are calibrated. This seems to happen every time, but only when the gravity gets lower, they are within a tolerable difference when the gravity is higher pre-ferment. WTF?
The refractometer is not that accurate post fermentation. Because alcohol is now involved, so to measure the level of sugar present the light reacts differently due to the concentration level. Because alcohol and water are now present this refraction is skewed and the alcohol refracts differently. So preferment there is only sugar and water present making a more accurate reading. There are charts out there on the intranets that adjust for this.
Ahhh, must have glazed over that part of the directions. Found this http://slobrewer.com/mobile/refract.html to be closest. I found a few different ones of these out there, others were not matching up to my readings, this came the closest. Seems to be a pretty complex conversion. Anyone know of other calculators?
more beer has one
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