Why has the Specific Gravity to Potential Alcohol conversions changed?

Ok, so I have implied but not said outright that I have been making wine for almost 30 years, but what I have also implied but not outright said is that there has been a break in that amateur winemaking career due to a divorce and moving across the country. You might notice some of my questions here, or posts elsewhere on the web were quite prolific, then I disappeared for a few years and I am back again.

Ok so this explains why I am asking this question. Below I am detailing my question.

Previously, I was sweetening my musts to target 1.100 in SG or a little more in order to get a decent ABV at 14-15%. However, for the last few weeks I have been using my hydrometer and noticing that 1.100 now corresponds to closer to 12.5% ABV. I have checked my old books and yes conversion tables ARE what I thought they were, but looking at conversion tables on the internet today show that 1.100 is between 12.3 and 12.7% ABV. What used to be universal appear to not be accurate and what is generally considered universal today doesn't match the past.

What gives? Are hydrometers and conversion tables entering in a calculated error to account for other solids in solution or what?

Topic conversion specific-gravity alcohol-content techniques homebrew

Category Mac

1
answered at

I was curious and poked around a little bit.

  • I remembered reading that hydrometers were previously calibrated at 60°F, whereas nowadays they tend to be calibrated at 68°F. Brewer's Friend describes the older calibration at 59°F instead of 60°.
    → However, that temperature shift has barely any impact, not the 1.5%-2.5% difference you note.

  • I also recalled reading that ABV can be calculated using multiple different equations. This page over at Brewer's Friend describes how their calculator implements two different equations. For an OG of 1.100 and an FG of 1.000, their "standard" results in an ABV of 13.13%, and their "alternative" results in an ABV of 14.20%.
    → I suppose it's possible that a different equation with even higher ABV results at higher gravities might have been more commonly used in the past.

Not definitive by any means, but hopefully this gives you something useful to work from.

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