Alright. So what’s the difference between calves’ kidneys, veal kidneys, lambs’ kidneys, ox kidneys, and pigs’ kidneys?

Types

Calves’ kidneys or veal kidneys

Calves’ kidneys (aka veal kidneys) are the Rolls-Royce of kidneys, and they tend to get hoovered up by the smart restaurant trade. They are the most tender and have the best flavour of all. Needless to say, they are also the most expensive. 

Lambs’ kidneys

Lambs’ kidneys are relatively easy to come by. They aren’t quite as wonderful (tender and flavourful) as calves’, but they are a very good substitute.

Rose Prince serves lambs’ kidneys by cutting a lamb kidney in half, and wrapping it together with a walnut of butter and some chopped parsley in a rasher of bacon. She then cuts the top third off a baked potato, an hour into baking, scoops a hole large enough to hold the wrapped kidney, inserts the kidney, puts back the top of the potato, wraps it in baking paper, and puts it back in the oven for another half hour.

Ox kidneys, beef kidneys, and pig kidneys

Ox or beef (an ox is simply a castrated bull) and pig kidney are tougher – ok for steak and kidney pie – and they have a rather strong flavour. They need to be soaked in salted water or buttermilk, and cooked more slowly in liquid.

Buying kidneys

They deteriorate faster than any other type of offal. They are best bought whole from a good butcher, and eaten the same day you’ve bought them. Don’t keep them longer than a day in the fridge.

Ask your butcher to take away the fat and the outer membrane and to halve them and cut out the white sinew inside, but buy whole kidneys and ask the butcher to prepare them according to your instructions rather than buying chopped kidneys (they begin to lose their flavour).

How to cook them

Get rid of the bitterness with salt

In order to avoid any bitterness of ox, beef and pig kidneys, the recommendation is to either salt them for about half an hour and then rinse; or to soak for a couple of hours in salted water (a couple of teaspoons of salt to 4 cups/1 litre water; or to soak them in buttermilk (easy enough to make with milk and lemon juice). It’s not necessary to soak calf or lamb, but it’s not a bad idea to salt then, rinse, and dry.

Grill or fry calves’ or lambs’ kidneys; braise or stew ox and pig kidney

Calves’ and lambs’ kidneys can be cooked quickly by grilling or frying. It’s very important not to overcook these otherwise they become tough.

Ox and pig kidneys need to be sliced and braised or stewed in a liquid for longer cooking time, as, for example, in a pie.

Method for cooking kidneys

1. Get rid of the bitterness by salting as described above. Sprinkle each half with pepper.
2. Fry with a little natural suet or some butter – about three minutes on each side, but be careful NOT TO OVERCOOK.
3. They should be brown on the outside and pink on the inside.
4. Serve with the Patum Peperium (if you don’t have any just mash in an anchovy fillet) butter or the parsley butter.

Ideas for dishes

Idea 1 – grilled on toast

Grilled calves’ kidneys are particularly good served on toast with Patum Peperium (Gentleman’s Relish) butter (mix the Patum Peperium into the butter in a ratio of about 1 teaspoon to 3 teaspoons of butter); or with parsley butter (mix about half a packet of butter with half a generous bunch of chopped parsley and a couple of teaspoons of lemon juice). Ask the butcher to supply the kidneys wrapped their own natural blanket of suet. You can use whatever suet remains to make some suet pastry.

Idea 2 – casseroled with gin

Ambrose Heath, in his Good Food on the Aga, says:

“The best way of all, to my way of thinking, is to cook it (veal kidney) whole in butter in a casserole, and just before serving to throw in a wineglassful of burnt gin and a few crushed juniper berries. This is quite wonderful, and if you can get the berries fresh from your own or a friend’s garden, so much the better.”

Idea 3 – old-fashioned, devilled

This is a traditional Victorian breakfast dish. The idea of devilling food in a hot spicy sauce began in England in the seventeenth century. Lightly fry the kidneys as described below and then add some brandy, Worcestershire sauce, cider vinegar, mustard and redcurrant jelly. Add a little double cream and serve with fried bread. For a full recipe of English devilled kidneys, follow this link. For a French version, go to Kidneys With Brandy, Cream and Mustard.

Idea 4 – cooked in their own fat

A very good way – and a classic way in Lyon – of eating them is in a mustard (Dijon and mustard seeds) sauce. This photograph is of rognons au Brazier. La Mere Brazier was a cook of titanic status – the first woman to win, in 1933, three Michelin stars, and a far-sighted employer who took on an apprentice named Paul Bocuse. The kidneys are exceptionally juicy as they are cooked in the fat that surrounds them.

How I came to discover all of this – considerable research!

In the process of recreating the kidneys with brandy, cream and mustard recipe for this month I went into my butcher and asked for calves’ kidneys. I’d arrived at the shop in a quiet period and instead of the usual knowledgeable manager I found three apprentices. They didn’t have calves’ kidneys they told me, but if I came back the following day I could have lambs’ kidneys… or ox kidneys.

“What’s the difference?” I quizzed

They looked nonplussed. Then one offered helpfully, “well, calves’ kidneys come from calves, lambs’ ones from lambs…. And oxes’ from oxes”

I assured them drily that I had already reached that level of expertise myself, and what I needed to know was more about  flavour, texture, culinary usage etc, but all they could offer in terms of further information was that they hadn’t often come across calves’ kidneys.

So I have done a lot of research: nearly twenty reference books, first fifteen Google search pages on three different key words, discrepancies checked with professional chefs, and my own trial and error.

Lucky I like kidneys!