The principle involved in measuring the specific gravity by a lactometer is that a floating object sinks until it has displaced a weight of fluid equal to its own weight. The greater is the volume of the displaced fluid, the smaller is the specific gravity of the fluid, and the lower is the lactometer reading.
- Dairy thermometer
- Mix the sample of milk well. Pour it into a dry cylinder which enables the lactometer to float without touching the sides.
- Let the lactometer into the cylinder. Take the reading from the lactometer as soon as it becomes stationary.
- Note the corrected lactometer reading (CLR).
Specific gravity = 1+ CLR\1000
SNF %( Solids Not Fat) = CLR\4 + 0.2xF + 0.36
Where F = Fat % in the milk sample.
Result and Interpretation
The lactometer reading taken at 84˚F (29˚C) is the corrected lactometer reading.