Explain the Indole Production Test?

Many microorganisms produce an enzyme tryptophanase which oxidizes amino acid tryptophan to produce pyruvic acid, indole and ammonia. We can analyze the production of tryptophanase by using SIM agar containing tryptophan. The presence of indole is then detected by adding Kovac's reagent which contains p-dimethyl amino benzaldehyde, butanol and hydrochloric acid. It produces a cherry-red reagent layer with indole (positive test).The role of acidified butyl alcohol is to extract the indole into the reagent layer which then react with dimethyl amino benzaldehyde.