The trick to rendering lard is to do it low and slow, so that the small amount of water in the lard can evaporate. But the lard must be pulled from the heat before it turns too dark or hot. It’s actually a very simple procedure: you heat the lard, strain it, and then cool it. But it takes several hours, so plan accordingly. The recommendations that follow are for rendering lard in the oven. Some people use a double boiler or a Crock Pot instead.
Grind the lard in a meat grinder or cut it into small pieces.
Turn the oven on to 300 or 325º. Put the lard into a heavy wide pan, such as a roasting pan, and put it into the oven.
Some people pour a very small amount of water into the pan first—just enough to cover the bottom—to keep the lard from scorching in the beginning. Eventually this water will boil away, but it takes longer to do it this way. If you keep an eye on the lard, it’s not necessary.
Stir the lard frequently. As the water evaporates the temperature will rise. Check temperature frequently with an Instant Read thermometer. Be forewarned that this will take a long time at low heat. As the lard renders, the cracklings (brown bits of crispy fried tissue that do not render) will float to the surface. When the lard is almost done and the cracklings have lost the rest of their moisture, they will sink to the bottom.
When the temperature reaches about 255º, remove the pan from the oven and allow the lard to settle and cool slightly. The lard will be a gold color, but it will turn white when it solidifies.
Carefully strain the lard through several layers of cheesecloth lining a sieve. Fill ice cube trays or muffin tins with the strained lard. This will allow you to easily take out a small portion when you need it. Cool, and then freeze. After it’s frozen, store it in Ziploc bags. It will last in the freezer for a very long time.