newbie question - specific gravity

Sorry, I know this has probably been asked a million times before but how do I convert the specific gravity to the alcohol content? Thanks

Reply to
Dee
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Ooops - didn't have sg at start!

Reply to
Dee

Yes, that's rather a key value to have. Next time you will!

If your wine is fermented dry, there is a gadget called a vinometer that tells you the percentage of alcohol in it. I find that it doesn't work so well, and I never use mine... but it is a cheap, narrow glass vial. If you can find one, you might try that at least.

Roger

Reply to
ninevines

Hi Roger

Same answer as before. This formula does not work. We can't end up with more alcohol than our original PA predicts. FWIW - Using the numbers from your example, I would "guesstimate" an end ABV of ~11.5% and about 1.2% RS. If a taste then indicated anything less than bone dry, I would get out my clinitest kit and see what was going on. (A whole different ball park from what your formula would lead you to believe). HTH

Reply to
frederick ploegman

I've seen this formula numerous times. Actually, I usually omit the sub-1.0 part, so 1.092 - 1.000 = .092 / .00736 = 12.5%

How do you figure this is wrong??

Roger

Reply to
ninevines

Hi Roger

My whole approach to winemaking is substantially different from what most folks seem to be doing now days, so please try to bear with me on my explanations.

The formula you are using is used to estimate *potential alcohol* with readings that are taken in a pre-pitch must (before the yeast is added). Before alcohol becomes part of the picture, the "TOTS" (Things other than sugar) has a specific gravity that approximates that of water closely enough that a hydrometer can be used to estimate sugar, and, based on this known amount of sugar and the average amount of alcohol that an average yeast can produce from a given amount of sugar, a PA can then be estimated.

The problem with using it once alcohol enters the picture (any post- pitch reading) is the fact that alcohol is less dense than water. As alcohol accumulates, it causes the hydrometer to float lower in the must than it otherwise would *and* for a reason that has nothing to do with the actual consumption of sugar. This can be viewed as the TOTS no longer approximating the SG of water and therefor causing a shift in the reference point that the hydrometer is calibrated for. (Hope this is making sense).

Let me try to explain it this way. For post pitch readings we wind up with a situation where the alcohol (less dense than water) is causing the hydrometer to float lower in the must, while the remaining sugar (more dense than water) is causing the hydrometer to float higher. The hydrometer cannot change it's calibration, so all such readings must be compensated for the shift in reference point caused by the alcohol in order to be valid. Knowing that a bone dry wine at ~10%ABV will give an end reading of ~0.990 should be enough to confirm what I am saying here. Lets take this a step further and say that we then resweeten this wine so it gives an end SG of

1.000. This reading will *not* then indicate a dry wine at 10%ABV, but a wine at 10%ABV with ~2.5% residual sugar !! Since this is observable in a wine that has been resweetened, it follows that the same thing applies to wines that have not yet gone all the way to dry (yet), but with the added complication that the sugar that remains has not been converted to alcohol (yet) .

Be glad to expand on this a little but be forewarned, I have been accused of having a rather odd way of looking at things! ;o) HTH

Reply to
frederick ploegman

Frederick, Please go on.. Get very technical 'cause I'm having a really hard time understanding this whole thing. I think this is my opportunity to learn it 'once and for all.' Please indulge me and the others here in RCW. Thanks, PJ

Reply to
PJ

equation is pretty much OK if your ferment stops at 1.000. Does it? Mine usually goes below that.

Here is the way I see it now. If you use pure water with an SG of

1.000, add enough sugar to it make the SG 1.0736, ferment all the sugar, the PA should be 10% ....not higher than that just because you now have water + alcohol....that is starting SG of 1.0736 minus 1.000 / 0.00736 = 10%. Since alcohol will bring the final SG below 1.000 because of its lower SG than the one from water, that final SG reading (0.995) will be the equivalent of the SG reading of water plus sugar (1.0736) minus the sugar for an SG reading of water only (1.000) or water and alcohol for a reading of 0.995.

Guy

Reply to
Guy

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