Every beef has two of these, so you might wonder why they aren't common in markets. Actually, there are several reasons. Many kidneys are destroyed in the USDA inspection process. Then there's the general degradation of American cooking knowledge, and most Americans are now so distant from the source of their food they've become squeamish about anything recognizable as part of an animal. In many ethnic cuisines this is a prized part of the animal.
I have a cookbook by a woman who married a Hungarian. Her husband gave her his mothers recipe and insisted on frequent servings of kidney stew. She dutifully made the stew but, being a good Eisenhower era American, couldn't stomach the thought of eating kidneys, so always made something else for herself. Then she got knocked up and dropped a kid. One day, after making separate dinners for her husband and the baby, she was just too tired to make anything for herself. In hungry desperation she tried the stew. Her reaction, "Hey, this is good!".
Veal Kidneys are smaller, more tender and with a milder flavor.
They can be treated in the same way as lamb kidneys, including quick
cooking by dry heat, but are not a good substitute for mature beef
Buying: In the days of my youth kidneys were common in supermarkets, but today are not seen there, at least not in California. You can, however, find them in specialty markets serving Eastern European, Russian and Mexican communities. Buy from a market that has a good turnover because organ meats are more perishable than muscle meats. Use kidneys the day you buy them, or store in the refrigerator, loosely wrapped or in their original tray, and use the following day.
Kidneys sold in North America are generally thoroughly cleaned and well prepared with all external membranes and fat removed. I prefer them nice and red, but parts contacting the shrink wrap can become a duller color. This is due to oxygen deprivation and isn't a problem so long as the kidney is fresh. It should not have a strong smell.
Yield: The photo specimen weighed 1.34 pounds. After cutting away all the inside fat it weighed 1.18 pounds for a yield of 88%. Beef kidney fat, called suet, is prized as the best beef fat for cooking, so if you render it for that purpose you'll be at nearly 100%.
Cooking: Beef kidneys, like pork kidneys, are generally cooked by wet heat and for a fairly long time to be tender. They should not be used as a substitute for lamb or veal kidneys in recipes with a short cooking time, and they also have a stronger flavor. Before cooking prepare as shown below.
If you find dealing with the whole kidney difficult, you can cut it in half lengthwise, or even into quarters.
You should be able to remove all the fat with almost no loss of kidney meat at all. The final result should look like the lower photo. You can now cut the kidney into pieces as called for in your recipe. Further processing depends on usage.
For Soup: You want to keep the soup from looking muddy, so parboiling is called for. Cut the the kidney into chunks or slices as best suited to later use or finish cutting. Put in a pot. Cover with plenty of cold water and bring to a boil over high heat (uncovered or it'll foam over when it boils). Rinse the kidneys and clean the pot. Repeat this process one more time.
For Frying: Kidneys are usually finish cut and fried before stewing or similar uses. After cutting I usually soak the pieces in 3 changes of cold salted water for about 1/2 hour total. Then drain thoroughly and fry.
Some recipes don't bother with this at all and some call for a soak in
milk which is supposed to be the most effective. Beef kidneys in the U.S.
today are generally from rather young beefs, so extreme methods to
"deodorize" are not necessary. Older recipes may presume an older animal.