Brewing Gravity and the Saccharometer
The number the Exchequer taxed, measured before the beer existed.
Origin
John Richardson coined the term saccharometer and published Statistical Estimates with the Saccharometer in 1784, bringing the hydrometer into general use among British brewers.
The catch
Original gravity is measured in the wort, before fermentation. It records how much sugar went in, not how much alcohol came out — so for a hundred and thirteen years the British Exchequer taxed beer on a number that is not the strength of the beer.
| Original gravity | Approx. finished strength | What it was | Under the 1880 system |
|---|---|---|---|
| 1000 | — | Pure water: the zero of the scale | No duty |
| 1030 | about 3% | Victorian mild, and the thin government ale of both wars | Well below the standard barrel |
| 1036 | about 3.6% | An ordinary modern bitter | — |
| 1043 | about 4.3% | Standard draught bitter | — |
| 1055 | about 5.5% | The standard barrel from 1889 onward | The reference gravity for duty |
| 1057 | about 5.7% | The standard barrel as first set in 1880 | Lowered in 1889: smaller brewers could not reach it |
| 1065 | about 6.5% | India Pale Ale brewed for export | Charged above the standard |
| 1100 | about 10% | Barley wine and old ale | The top of ordinary commercial brewing |
The instrument has a disputed parentage. Benjamin Martin built a specific-gravity hydrometer in 1762 and advertised it for testing beer, ale, wine and worts, then became so confused by his own readings that he declared it useless and abandoned the work. James Baverstock bought one of Martin’s instruments in 1768 and, working systematically, demonstrated exactly what it was good for. John Richardson coined the word saccharometer, published Statistical Estimates with the Saccharometer in 1784, and persuaded the large London brewers to adopt it. Baverstock published his own findings in 1785 — a year after Richardson had claimed the originality. The Excise took the instrument seriously. Bate’s saccharometer became the reference instrument for specific gravity, and officers kept it locked up. Scotland had used Allan’s saccharometer under an Act of 1816 until Bate’s replaced it there in 1825. The Inland Revenue Act of 1880, usually called the Free Mash Tun Act, abolished the malt tax that had stood since 1660 and taxed the wort instead. That freed brewers to use whatever materials they liked, which is why the Act matters to brewing history as much as to measurement, and it made original gravity the basis of the duty. Readings were corrected to a standard temperature of 57°F, later 55°F, and official tables converted the gravity lost in fermentation back into the original figure. The weakness is in the catch above. Gravity before fermentation does not fix the strength after it, because that depends on how far the yeast attenuates — two beers of identical original gravity can finish a full percentage point apart. Britain finally moved beer duty onto alcohol by volume in June 1993, measuring the drink rather than the ingredients.