In the brewing industry, the Plato scale (degrees Plato, °P) is a measure of sugar concentration of the wort before fermenting. It is very similar but not precisely the same as the Brix scale used in wine-making, named after one Adolf Brix. But all my usual sources are coming up dry on the origin of the Plato scale. I can’t see any obvious connection to the philosopher. Anybody know?
“Plato: The liquid-density scale invented by Carl Balling was later corrected and modified by a Dr. Plato of the German Imperial Commission; the Balling scale now reads in degrees Plato.”
- Marty Nachel, Homebrewing for Dummies (1997), p. 379
According to this page the scale was invented by a Mr Plato. Probably not the philosopher, though.
This page on the very splendid Beerhunter site mentions that the scale is German, so perhaps it was named after a Herr Plato instead.
It seems that although Plato (or Balling) is similar to Brix, it is a measure of fermentable sugars, rather than total sugars which is what Brix measures.
It measures the density of a fluid in comparison to water (when at 60 degrees F). Sugars are denser than alcohol or water, so you use the change in readings from the start of fermentation to the end to calculate the percent of alcohol by volume.
The quantum leaps in brewing technology that occurred during the Industrial Revolution were fired, in part, by the application of basic scientific methods to improve consistency and quality of beer. The two most important measurements needed then, as now, were temperature and wort density. Brewers needed to know how much fermentable extract they had in their fermenter.
Gak! Beat me even when I preview! 
Being European scales, both Balling and Plato are calibrated at 17.5°C. Brix is calibrated at 15°C which is pretty close to 60°F. I think we’re starting to split hairs.
Ah, I missed how the scale was calibrated; that’s useful information. Thanks!
For what it’s worth, I think more homebrewers - at least in the US - use the specific gravity scale rather than the Balling scale. On this scale, water at 60F is 1.000, gasoline is around 0.66, whole milk is about 1.028, and mercury is 13.600. (Numbers taken from Nachel’s book, as cited above.)
And Tapioca Dextrin, you’re right - that’s specific gravity’s calibration point. I failed to notice which scale was being cited when I was checking the book.
What’s this? Herr Doktor Plato went through life with no first name? You people disappoint me.
But seriously, thanks for the answers, folks.
Slave driver
Plato, they say, could stick it away–half a crate of whiskey every day!
silenus, please do not copy/paste entire paragraphs from other websites.
You may copy a small part from other websites and then link to the source for the rest of the article.
Please read the FAQ and Registration Agreement before you make your next post.
Thank you.
-xash
General Questions Moderator
Actually, the Balling/Plato scales measure % sucrose by weight in water, so it’s temperature independent. In other words, a 10 degree wort is a 10 degree wort, regardless of whatever temperature it’s at.
SG on the other hand is relative to temperature- everything’s pegged back to 60 degrees F for comparison purposes.
http://www.brewingtechniques.com/library/backissues/issue1.3/manning.html
Okay, now I’m impressed. Thanks.