Ray or Andy - UC Davis link

I see some have already given it too you. In the future you can find it on the left side of the page on Jack Keller's Wine Blog. Might be a convenient place to remember it.

Ray

That's just their home winemaker manual. It's not the course material they had around there somewhere. Frederick,

I wonder if they took it off their site.

Andy

Probably since the sell their course now. I understand it is quite pricy.

Ray

Here is the one I was referring to:

Not very detailed but it does show how they arrive at PA. (see second to the last para on page 10 for an example) I don't seem able to find the more detailed material any more. Sorry.

Frederick

Frederick:

Ok, thanks, that's good enough. The discussion there makes sense, I've got no problem with what they're saying, apart from the fact that the 2 constants they use (0.59 multiplication factor and 3 B subtraction for solids) are not supported by clear references - I've seen other numbers in different formulas.

One point, though - this is not what the hydrometer scale is based on. Hydrometer PA scale is linear (as a function of B or sg), but their formula isn't because B is multiplied by sg, so in higher B ranges, 1 B drop in the scale gives more alcohol then in lower B ranges. I'm bringing this up because I'd really like to know what the hydrometer scale is based on - maybe it is derived from lots of research data, as you suggested, but it's not this research.

Pp

frederick ploegman wrote:

See NBS Circular C 440, Polarimetery, Saccharimetery and the Sugars by Bates et. al, Table 109. Keep in mind it's a pretty sterile enviroment they were working in; pure sucrose was used for the hydrometry values, that's why it's so precise. They used modulus 145 for the Baume values, which is ofte called PA.

The reason everyones PA values differ is it's just a SWAG, it doesn't mean much. It's all ballpark since there are too many variables. Dissolved solids in the must and fermentation temperature affect alcohol content. Even the relative humidity barrel aging occurs at affects the volume of alcohol remaining.

The values just get you in the ballpark, it seems they were never meant to be used as anything other than a place to start from.

Joe

Not exactly correct. The tables are actually different and meant to be used differently. There are several different tables based on different assumptions. You really need to understand the original table to use it. This is explained in "The Unified Theory of Gravity", Wine Maker Mag., April-May 2004, Vol. 7, No. 2. If the tables are applied correctly, as the original authors intended, they all give the same or very similar results. Fred and I do not agree on those results but that is another story. He does not agree with the way Berry, Duncan, Acton, and many of the other original authors do their calculations. At least you can make published tables yield similar results so they are not as ball park is it may seam.

Ray