Use: test for screening, rapid assessment of acidity.
Advantages: quick, cheap.
Proteins in milk that has become sour (i.e. because of lactic acid formation) will coagulate when mixed with alcohol.
Equipment and materials:
- Test tube.
- 68% ethanol solution (by weight: e.g. mix 68 ml 96% alcohol with 28 ml distilled water) or 75 % ethyl alcohol by volume (density 0.8675 g/ml at 27 °C).
1) Mix equal amounts (e.g. 2 ml) of milk and ethanol solution in test tube with the pipette.
2) Agitate by gentle movement and look for coagulation.
Milk containing more than 0.21% acid and milk that is abnormal (e.g. colostrum or mastitis milk) will not pass the test. This milk is not fit for further processing.