Homebrewers Association  AHA Forum
General Category => General Homebrew Discussion => Topic started by: nyakavt on February 09, 2010, 07:21:39 PM

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 (http://beerbarons.org/pdf/brewingCheatSheets/refractometerBrixToSGConvertion.pdf) which says Plato = 1.04 * Brix. I'd like to get another source or get verification of the accuracy of this conversion.

Degrees Brix (symbol °Bx) is a measurement of the dissolved sugartowater 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.

I found this table (http://beerbarons.org/pdf/brewingCheatSheets/refractometerBrixToSGConvertion.pdf) which says Plato = 1.04 * Brix. I'd like to get another source or get verification of the accuracy of this conversion.
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.

I found this table (http://beerbarons.org/pdf/brewingCheatSheets/refractometerBrixToSGConvertion.pdf) which says Plato = 1.04 * Brix. I'd like to get another source or get verification of the accuracy of this conversion.
That's a refractometer conversion factor.
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.

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.

That's a refractometer conversion factor.
that's the quick factor, but above 1.050 or so it starts to deviate. the real formula is
Well, we're talking about two different conversions. The factor of 1.04 converts refractive index to °Brix for wort. What you're talking about is the conversion from Brix (or Plato  as nyakavt found in Excel, the difference is negligible) to SG. That's where the "multiply by four" rule gets thrown out a lot, even though it isn't particularly accurate.

That's a refractometer conversion factor.
that's the quick factor, but above 1.050 or so it starts to deviate. the real formula is
Well, we're talking about two different conversions. The factor of 1.04 converts refractive index to °Brix for wort. What you're talking about is the conversion from Brix (or Plato  as nyakavt found in Excel, the difference is negligible) to SG.
ah  now that I reread, I see where you were going.
That's where the "multiply by four" rule gets thrown out a lot, even though it isn't particularly accurate.
yep  I swear a lot of people's 'refractometer problems' emerge from this  that's why I tried to point that out, but didn't realize you were talking about a different conversion.
Cheers!

Degrees Brix (symbol °Bx) is a measurement of the dissolved sugartowater 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.
So a 25 °P solution would have 25 grams of sugar or dissolved solids.
Sounds like the same thing.

+1 to Sean
Brix, Plato and Balling did the same thing. They came up with a table to convert specific gravity to % w/w sugar. I believe all used sucrose. In brewing we don't have just sucrose but we pretent as if it was all sucrose. That works for hydrometers because that's how the scales have been defined. As Sean said, it doesn't work for refractometers anymore. Since refractometers tend to read Brix many think that the 1.04 is a Brix to Plato conversion. It could also be a Brix to Brix or Brix to Balling conversion. It would be much less confusiong if the refractometer would read the refractive index and we had a RI to Plato conversion instead. On the same lines I could also make a refractomter for brewers that reads Plato.
Kai

I just listened o a great archive from "the Session", on brewing calculations. Check this link out. All kinds of good stuff here. IIRC, the point you want is an hour or so in.
It was aired on 91309
http://thebrewingnetwork.com/shows/553