Bierenliefhebber
Active Member
- Joined
- Aug 24, 2011
- Messages
- 42
- Reaction score
- 2
Mostly for my own amusement, and as an exercise to maintain my rusty programming skills, I recently wrote one of those programs to predict S.G. as a function of the grain bill. It was when I attempted to incorporate hydrometer temperature corrections that I ran into trouble. Now, I dare say I'm no babe in the woods when it comes to physical chemistry - I have degrees in both chemistry and the biological sciences, yet, I can discern no consistent manner for correcting hydrometer readings from authority to authority. Papazian recommends simple, across-the-board additive corrections, independent of the SG of the wort. Dave Line's book, on the other hand, describes a multiplicative correction, that therefore produces a higher degree of correction for stronger worts. At higher temperatures and specific gravities, this leads to wildly different calculated gravities from those given by Papazian's simple correction chart.
Of the online calculators, only that at HBD.org reveals their methodology: this calculator appears to be a Javascript implementation of a formula derived by C. Lyons and based on values in the CRC handbook. However, those original values are based on the SG of pure water at various temperatures, and thus do not reflect any contribution - which surely must exist - by dissolved sugars. Finally, there is the Fermsoft.com calculator. They do not actually describe their methodology, but comparing results obtained by plugging in SG values for worts of 1.010, 1.050, 1.070, and 1.100 at different temperatures from 10 to 90C shows that their method apparently does indeed incorporate some sort of correction factor for worts of different densities.
The bottom line here is that if anybody knows of any definitive discussion concerning hydrometer corrections vs. temperature vs. wort gravities, I'd be delighted to learn about it.
Of the online calculators, only that at HBD.org reveals their methodology: this calculator appears to be a Javascript implementation of a formula derived by C. Lyons and based on values in the CRC handbook. However, those original values are based on the SG of pure water at various temperatures, and thus do not reflect any contribution - which surely must exist - by dissolved sugars. Finally, there is the Fermsoft.com calculator. They do not actually describe their methodology, but comparing results obtained by plugging in SG values for worts of 1.010, 1.050, 1.070, and 1.100 at different temperatures from 10 to 90C shows that their method apparently does indeed incorporate some sort of correction factor for worts of different densities.
The bottom line here is that if anybody knows of any definitive discussion concerning hydrometer corrections vs. temperature vs. wort gravities, I'd be delighted to learn about it.