At the Domaine d’Esthine, Brigitte Pieau uses cold saponification, which guarantees a natural surgras soap. The mixture of donkey’s milk, vegetable oils, essential oils, and caustic soda is first lightly heated. It is then mixed for a few minutes and the resulting paste is poured into moulds. Saponification continues until the soap hardens. The soaps are then cut out, stored, and dried for six weeks. This drying cure is essential because it allows the soaps to last longer.