Complex sentence: When milk is added to ginger juice, protease reacts chemically with the protein in milk which changes from a water-soluble form to a water-insoluble form, and leads to the formation of milk curd.
Split into simpler sentences: When milk is added into ginger juice, protease reacts chemically with the protein in milk. Then, one kind of protein in milk would change from a water-soluble form to a water-insoluble form, and leads to the formation of milk curd.