Casein Substrate, Concentrated

Suspend a quantity of casein EPBRP equivalent to 2.5 g in 5 mL of water, add 18 mL of 0.1m sodium hydroxide and stir for 1 minute. Add 60 mL of water and stir with a magnetic stirrer until the solution is practically clear. Adjust the pH of the solution to 8.0 with either 0.1m sodium hydroxide or 0.1m hydrochloric acid and add sufficient water to produce 100 mL.

Use on the day of preparation.