Mustard seeds contain roughly equal amounts of protein, carbohydrate, and oil. When ground, the protein and carbohydrates bond with oil – coat it actually – and keep it from repelling the water in lemon juice, mayonnaise, vinaigrettes, etc.

According to Harold McGee, author of On Food and Cooking, the coating of the mustard seed also contains a fair bit of mucilage (a thick, sticky, gluey substance with an icky name), and this also helps to coat particles of oil, allowing them to coexist harmoniously with watery substances.

McGee says as much as 5% of the seed weight of the white mustard seed can be mucilage in the coat of the seed. White mustard is often used in sausage-making, he says, to help bind potentially repellent bits of meat.