Alcoholic solution of alizarin 0,05%
Alizarin is used as an indicator because it has a yellow color at pH values below 5.5 and red when the pH is greater than 6.8.
How to use:
In a test tube 3 ml of the sample of milk examined are stirred and 3 ml of alcoholic solution of alizarin, which acts as an indicator. If the milk is fresh, it takes on a yellow color without coagulation; if instead the milk is acid, it takes on a yellow-orange color with the formation of lumps and flakes.