Cut the fat into 1" or smaller chunks, grind it or process in food processor. Approximate rendering time for small chunks is 10-15 hours or 8-10 hours for ground or processed fat.
Place the fat in a large, heavy pot or a large roaster. Add about 1/2" water to the bottom. Heat over medium-low heat until water is simmering. Continue cooking for about one hour, stirring frequently. Cover the pot and put in 225° oven or roaster. Leave untouched for 8-10 hours, this is a great over-night project.
Bring the pot back to a rapid simmer, stirring frequently. If the pieces of fat have sunk to the bottom, are shrunken and very soft, you're done rendering. If not, continue the rapid simmer. Remove from heat and cool for 15 minutes. Using a metal colander and a large coffee filter or cheesecloth, pour rendered lard into filter to separate liquid from the cracklings. Unless your cracklings are already crisp and brown, return them to the pot and continue to cook them. They will brown to a golden color and continue to give up liquid lard. When cracklings have browned nicely, repeat filtering process.
Cool lard for about 1 hour then transfer to canning jars or freezer containers. Store in refrigerator for up to four months or in freezer for up to one year. Try using the cracklings in cornbread, biscuits, bread, soup, salad toppings or salted as a snack.
Note: If the pork fat has skin attached it will give off a stronger smell during rendering.