"Revenge is black-pudding" That appears to be the expression used in the English translation of the book. I found it using Google's book search.
http://www.google.lu/books?hl=en&id=ED...enge&pgis=1If the Germans don't normally say "Rache ist Blutwurst", and the original author didn't choose the customary German expression, there would seem to be an argument for translating it literally. Otherwise, the original image (conjuring up images of blood and guts) would be lost.