The French white sausage, boudin blanc,
is made from various white meats bound together with milk, eggs, bread crumbs,
or flour,
while the black boudin noir contains no meat at all: it’s around one-third pork fat, one-third onions, apples,
or chestnuts, and one-third pork blood,
which coagulates during poaching to help provide a solid matrix. Liver sausage is made by cooking a blend of finely ground liver and fat.