Simple procedure for showing presence of milk proteins in clarified butter (ghee) By clarifying butter, e.g. by melting butter and filtering it, we rid ourselves of most of the protein in the butter, and are left with mostly fat. However, the separation of protein and fat is not complete. Some people cannot eat milk proteins due to allergic reactions, and cannot therefore use unrefined butter in their cooking. 

Is there a simple "home-kitchen" procedure to test whether the filtration sufficiently removed the milk proteins? Any proteins in the ghee can be precipitated by adding acetic acid, but this is not specific to milk proteins. 

Does anyone have any ideas?
A classic test for protein is Biuret solution, using readily available reagents:  sodium hydroxide, copper sulfate and potassium sodium tartrate (Rochelle salt). The test is not specific for milk protein, but what other protein would be in pure butter?

Use caution with the chemicals -- the first listed is quite caustic, and the second is poisonous. BTW, save some leftover Rochelle salt if you'd like to make a piezoelectric crystal.