Why does the milk curdled when it is mixed in vinegar?
Acids (like acetic acid which is in vinegar) will denature protein Milk contains proteins, mainly one known as casein. Much in the same fashion as the proteins in egg whites (albumen, which contains a mixture of proteins) denature when heated, turned them from their reasonably transparent appearance to the white, essentially solid material (with the gelatin like texture). In both cases, whether the proteins are being denatured by a chemical process or by a physical process, the result is the protein begins a breakdown, and the new configurations of these molecules make them likely to congeal and stick to together, forming a semi-solid…curds in this case.
