Reading a HydrometerHydrometers measure Specific Gravity
Water has a specific gravity of 1.000
Adding sugars to water will increase it's gravity.
As the yeast ferments the sugars and converts them to alcohol, the density of the wort will reduce.
A 1.040 reading is more often referred to as ten-forty.
Each increment (short line) on the hydrometer represents 2 gravity points.
The long horizontal lines refer to the number above them for eg. the line under the orange band (shown) represents 1040.
The gravity at which you make up your wort to and fermentation starts at is the Original Gravity or OG.
The gravity at which fermentation finishes is the Final Gravity or FG.
To calculate approximate alcohol content subtract FG from OG and divide by 7.5, for eg (1040-1010) / 7.5 = 4% abv
Once the original gravity has been noted there is little point taking a reading of the beer until the yeast head has completely subsided.
Once the yeast head has subsided a sanitized hydrometer can be left in the wort and a reading can be taken by lifting the fermenter lid and having a quick look.
Hydrometers are cheap, buy two, they break easily.
Hydrometers are only accurate at 20 deg c, if the temperature of the wort or beer is different adjust accordingly
