I know someone will ask - how to you render fat.
Well, most of you have been doing that all along. When you cook meat and pour off the fat - you have rendered fat. When you put the juices from cooking meat or making soup into the refrigerator so the fat will rise to the top and you can skim it off - that's rendered fat.
You could collect this fat and use it for cooking - it won't be "pure" in that there'll be meat juices in it. When I collect fat this way, I take the cold, solidified fat from the top of the liquid, break it up, and store the pieces in the freezer - and use straight from the bag.
However, a more pure form of fat is rendered by cooking just the fat with no meat so the fat is melted out of the fiberous material. You strain this through a mesh while pouring into a dish. Let it solidify in the refrigerator, break it in pieces, and keep in the refrigerator, or if a lot, put the excess in the freezer.
There are excellent tutorials on the internet to help one learn how to render fat - and some videos. Just do a search and find the way you like best.
There are two basic ways to do this
1) put the fat in water and slow boil for an hour or so. When cooled down, place the pan in the refrigerator. You can then lift the solid fat up from the water.
2) slow cook it on stovetop. You don't have to contend with the water this way.
WHERE TO GET THE FAT
I buy beef fat from Whole Foods - they charge me $1/lb. The reason is that the beef from there has not been given hormons or antibiotics. It is in the fat that the hormons will be concentrated. So for quantity tallow, I go for the better raw ingredients. That's not to say that I don't skim fat when cooking regular grocery store beef, but it is a smaller part of the whole for us.
Chicken fat: we don't like the skin on our chicken. So when I skin the thicken thighs I cut off some of the fat, and put the whole mess in a pan of water and slow boil it to render the fat. It isn't "pure" in that it hasn't been strained, but since I keep it in the freezer, this isn't a storage problem.