Suet is beef or lamb fat that is generally taken from around the loins and kidneys of the animal. It is a soft fat with the consistency of shortening and a marbled pink-white color. When I was younger the butcher in the grocery store would give away suet for free. However, today more and more supermarkets are actually selling packaged suet. If you don’t see it in the meat case, it never hurts to ask the butcher for some. Suet should be stored in the fridge and used rather quickly or stored for longer periods of time in the freezer. Shortening is a good substitute.
Suet is often converted into tallow through a process called rendering. This involves simmering and filtering it to isolate the fat from any solids. This process is also used to render lard from bacon fat and ghee from butter. Once rendered, tallow can be stored for a much longer period of time without requiring refrigeration. It should be stored in a sealed container away from light to prevent oxidation and spoilage of the fat. Tallow is used in cooking and to make soaps and candles.
Suet was commonly used in Medieval times to make a variety of sweet and savory dishes. Today butter and shortening have largely replaced suet, but it is still used in several British dishes such as Christmas pudding, spotted dick, Yorkshire pudding, and black pudding. It is also used in mincemeat and in pie crusts and pastries (check out Suet Pastry for a recipe). Vegetarian suet is also available in some specialty stores. It is made from a vegetable fat such as palm oil that is mixed with rice flour.
Wild birds including woodpeckers, wrens, nuthatches, thrashers, cardinals, and starlings love suet. These birds normally eat insects and suet serves as a good high-calorie, high-fat substitute, especially during colder seasons when insects are less plentiful. The suet does not have to be rendered to use it as bird food. It can simply be spread into tree bark or on a pole. However, rendered suet does keep for longer periods of time, especially during the summer. It can be purchased in stores that sell birdfeed or you can render your own suet. Chop it into fine bits and heat it in a pan over medium heat until all the fat has melted. Strain the liquid through a fine strainer or cheesecloth to remove the solids and let the suet cool. This first rendering produces suet that is still rather soft. A second rendering will make a much firmer suet. It can be molded into cakes by pouring it into circular containers such as those in a muffin pan. Additional goodies like nuts, seeds, and bird seed mix can be stirred into the suet before it hardens.
You can set out cakes of suet year round, but avoid a pool of melted suet by using it only when temperatures are cooler than 70 ° F. They are commonly placed in a special mesh feeder that is attached to a tree trunk or pole about 5 feet off the ground. The cakes can also be placed in a mesh bag or even just placed on the ground. Beware of the last option, however, as squirrels also love suet.
http://www.birdsforever.com/suet.html
http://www.bcpl.net/~tross/by/suet.html