These are my hydrometers. The Mickey Mouse one designed for homebrewers has a range from 9 to 110 along a 75mm stem, and the three professional ones cover the ranges shown along 120mm stems. The bulb and stem diameters of the little one are 180mm and 66mm, and of the others 400mm and an incredibly fragile 4mm.
The two on the right were amongst a heap of stuff being ditched by a disgruntled brewer who had just lost his job when Ind Coop decided to close Halls micro-brewery, which they had inexplicably installed in their enormous distribution centre in Plymouth. In one of those instances of being in the Right Place at the Right Time, I came away with them, a Maxi cooler, an electronic temperature controller similar to an Ink Bird, a quarter of a pocket of Hops (most of which I traded for malt at the local homebrew shop), and some other goodies, in exchange for a couple of bottles of spirit.
As I have explained elsewhere, I only conduct a single fermentation over a period of a week, and use no priming sugar, so knowing the gravity to one tenth of a degree, rather than plus or minus 2 degrees, is essential in timing the cooling of the FV to leave sufficient fermentables for conditioning when it goes into the PBs. I aim for a PG (present gravity) of 13 at racking, as experience has shown I will need to add hardly any CO2 from a S30 cylinder during dispense. If the yeast has caught me out and the racking gravity is 8 or less, I will be adding gas all the time.
