Appearance
Fresh milk should be slightly viscous, white with a yellowish tinge depending on the fat content (the fat content varies with the species of animal, the breed and the time of year). There should not be discoloration, lumps in the milk or a high viscosity. It should have a bland, slightly sweet taste and a pleasant smell. If a spoon is dipped into a sample of milk and slowly withdrawn, there should be no strings or threads of milk.

Density
The density of milk can be measured using an instrument known as a ‘lacto-densimeter’ (or ‘lactometer’) . If a low reading is obtained, it indicates that the milk may have been diluted with water.

Bacteria
A microbiological test that is appropriate for small-scale dairy processors is the ‘methylene blue’ test. Other tests are either too expensive, or require the specialist equipment and skills at a university Food Science department or Bureau of Standards.

The method is:

1. Mix a 20 ml sample of milk to ensure that the cream is evenly mixed in.
2. Place in a test tube and add 0.5 ml of dye solution (the dye is a 0.0075% solution of methylene blue). The liquid dye should be stored in a foil-covered bottle in a cool, dark place away from sunlight, and can be kept for 2 months.
3. Seal the tube with a stopper and mix the contents by inverting the tube.
4. Hold in a covered water bath at 36-38C, so that the sample remains in the dark.
5. Record how long it takes for the dye to fade (as an indication, if the colour remains for 30 minutes2 the milk has a satisfactory quality.

Other tests
Measuring the fat content of milk requires chemicals and laboratory apparatus that are not likely to be affordable in a small dairy, and samples should be taken to a Bureau of Standards or university Food Science department for testing. A low fat measurement indicates that some of the cream has been skimmed from the milk or that it has been diluted with water.