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Brix to plato conversion

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nyakavt:
Everything I've read online say that Brix and Plato are 'close enough' for brewing.  Well this isn't very satisfying to me, I would like to make that decision myself.  Promash never displays the same value for plato and brix when I enter my refractometer reading.  So, how does one convert between the two?

I found this table which says Plato = 1.04 * Brix.  I'd like to get another source or get verification of the accuracy of this conversion.

bluesman:
Degrees Brix (symbol °Bx) is a measurement of the dissolved sugar-to-water mass ratio of a liquid. It is measured with a saccharimeter that measures specific gravity of a liquid or more easily with a refractometer. A 25 °Bx solution is 25% (s/w), with 25 grams of sugar per 100 grams of solution. Or, to put it another way, there are 25 grams of sucrose sugar and 75 grams of water in the 100 grams of solution.

Degrees Plato are used in the brewing industry to express the concentration of extract (dissolved solids, mostly sugars) in a wort or beer as a percentage by weight. Thus 100 grams of a 12 degree Plato (abbreviated 12 °P) wort contains 12 grams of extract.

a10t2:

--- Quote from: nyakavt on February 09, 2010, 12:21:39 PM ---I found this table which says Plato = 1.04 * Brix.  I'd like to get another source or get verification of the accuracy of this conversion.
--- End quote ---

That's a refractometer conversion factor. Degrees Brix and degrees Plato are the same thing (within 0.1% anyway), but a refractometer doesn't read either - it simply measures the refractive index. It then correlates that RI to a °Bx scale, for a sucrose solution. Unlike grape juice or honey, wort isn't a sucrose solution, hence the conversion factor.

blatz:

--- Quote from: a10t2 on February 09, 2010, 01:53:50 PM ---
--- Quote from: nyakavt on February 09, 2010, 12:21:39 PM ---I found this table which says Plato = 1.04 * Brix.  I'd like to get another source or get verification of the accuracy of this conversion.
--- End quote ---

That's a refractometer conversion factor.
--- End quote ---

that's the quick factor, but above 1.050 or so it starts to deviate.  the real formula is

=1.000898+0.003859118*BRIX+0.00001370735*BRIX*BRIX+0.00000003742517*BRIX*BRIX*BRIX

if I remember correctly, this formula corrects for Plato:

=1.000019+(0.003865613*Plato+0.00001296425*Plato^2+0.00000005701128*Plato^3)

however, the OP was more concerned with Brix to Plato and vice versa conversion, of which I am not familiar.

nyakavt:
I plugged Blatz's formulas into excel and got an average difference of 0.87 SG points between the two scales.  Plotting Plato vs. Brix, the trend line is:

PLATO = 1.0000267*BRIX - 0.0009006
R² = 0.9999999

This was a curiosity because the refractometer conversion factor is defined as:

Refractometer reading in Brix / Hydrometer reading in Plato

I guess the refractometer conversion factor takes care of the slight difference in the scales by its definition, I was thinking that there was some unaccounted for error.

So suppose you make up a solution of water and sugar that measures 1.04003 SG, or 10 Plato.  Since this is pure sugar, the Brix reading will also be 10 Brix.  But if the sugars in solution are made up of more than just sucrose, as in wort, the Brix reading will be slightly higher.  10.4 if we use a 1.04 refractometer conversion factor.

Thanks for the explanation.

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