WW notes that the recipe says that brawn made of a pig's head is "seasonable from September to March."

Somewhere in Jeffrey L. Steingarten's second book -- It Must've Been Something I Ate: The Return of the Man Who Ate Everything, he relates a trip to Paris to witness the slaughter of a 400-pound pig, the collection of its blood and the creation (and canning) of the perfect boudin noir. In the essay, he mentions that pigs are properly killed only in the winter in France. Why this is true, he does not disclose.