SG/PA Table source

Well they all have to be based on the yield of alcohol produced, which is dependant on the individual yeast strain and fermentation environment. The theoretical yield is 51.1% alcohol/weight but practical values differ. For example, fermenting at higher temperatures tend to lower the value - say 43%. Thus the discrepancy in many tables (aside from volume changes etc as the conversion of sugar to alcohol + CO2 takes place which maybe aren't factored into many tables). The quantity of alcohol produced is then calculated using this yield from the sugar solutes (measured as Brix, SG, etc).

For example, assuming an alcohol yield of 47%/weight, a must with 24% sugar by weight (Brix 24) would give 11.3% alcohol by weight when fermented to dryness. Given that the density of ethanol is 789 kg/m^3, this is 14.3% alcohol by volume.

HTH, Ben

Most of the tables I have seen are in fairly close agreement. I want to see how they came up with the tables. Empirical or theoretical or what and what was taken into account.

Ray

Isn't the Specific gravity of distilled water 1.000? If so, that's the basis for the SG scale. Potential alcohol is just a function based on measurements of a must.

Degrees brix represents the percent of sugar in a must by weight, IIRC. Degrees brix as a name probably came about as a way of differentiating from degrees celcius. IDK if any of that's correct but it seems logical. Perhaps I'm not understanding your question?

Yes, Specific gravity of distilled water is 1.000 and that is the basis of the SG scale. Of course not all of the SG difference when you measure a must is due to sugar. The general rule of thumb is .005 to .007 is caused by other large molecules or fruit particles.

The PA scale is different. It is the Alcohol that can be expected from a given amount of sugar. What I am trying to determine is how much of the published scale is empirical and how much is theoretical. In other words, was it developed by predicting the theoretical yield of alcohol from sugar that would be determined from the chemical equation, or was it determined by fermenting known sugar concentrations and then measuring the alcohol yield in a lab. Not all sugar is converted to sugar. I know many will say the by products would cause only a small error but I am not at all sure that is true. I think the error could be as high as 2 to 3% of a 12% wine, or as high as a 25% error in determined alcohol. I may be wrong but I what to see how they developed the PA table rather than working from anecdotes of how accurate it is. There must be some technical books that go beyond superficial treatment of this scale.

Ray

What makes you think that the errors would be so high?

One suspicion is the formation of glycerin. My understanding is that it forms early in the fermentation process. If one percent of glycerin forms it uses the sugar that would have formed one percent of alcohol. Glycerin can be a good thing in wine but it could be a significant error in calculating alcohol from SG. Action and Duncan state that most wines have between 1 and 2 percent glycerin but the amount of glycerin can be increased if sulfate is added. They even comment that this technique was used during WWI to manufacture glycerin. They do not indicate that glycerin is taken into account in their tables. In fact, it looks like it is not. I am just trying to get a handle on what IS taken into account in the table. I assume that it was developed by someone and it must be published somewhere.

Ray