It is the cheapest of animal fats, the more suitable for certain preparations and, at least in Italy, the most underestimated. And if it is obtained from adult animals but not exhausted by fatigue, must be a nice yellow, firm to the touch and not crumbly.
You shouldn’t use kidney fat for frying because it makes the frying frothy. In Muslim regions is also used to fry the fat of mutton.
We use fat such as lard, seasoned with sage and rosemary during the dissolution. You can filter and use maybe mixed with oil at a ratio of two to one, especially for frying the potatoes and vegetables generally served very hot.
Small amounts of natural kidney fat (not melted and filtered) can be added to lean ground meat, in proportion of one to four, to make it softer, delicate and tasty.
The kidney fat can give softness to a mess of macaroni or a timbale of rice, a sauce of crumbled up giblets and sweetbreads, pigeon or chicken and simmer. The essential condition is that everything is served hot and the fat is of excellent quality and above all very fresh.
During the war, it was prepared a kind of fake butter, melting the fat of kidney with many flavors, filtering and mixing it with a little water, into which there was dissolved salt and powdered milk. It is also used for pasta sauce, which is not unpleasant if served hot.