Drops of Kovac substance into the tube solution leave tryptone is 20 minutes notice colors above substance. If it does not produce the yellow, but if it is a dedicated manufacturing Indonesia will be purple.
Drops of Kovac tryptone solution into the tube and leave it for 20 minutes observing the color of the top. If not produce indole is yellow. If the product indole is purple.
Kovac dropping down a tube tryptone solution for 20 minutes notice the color on the top of, if do not produce indole is yellow. But if produce indole is purple.