Chop the fat: Remove any red meat from the fat and then finely chop the fat, which will make it render more easily.
Render the fat: Add water to the bottom of a Dutch oven or large pot, then add the chopped beef fat. Place over medium-low heat. Stir occasionally every 30 minutes or so with a wooden spoon for 2 to 4 hours, or until most of the fat is rendered.
Strain the fat: Let cool slightly, then scoop off and discard large solids with a spider or slotted spoon. Line a fine mesh strainer with a paper towel, cheesecloth or coffee filter and set over a glass or metal container that you can easily pour with. Pour fat through the lined strainer while hot. **See note.
Pour into storage containers: Optionally transfer from the pouring container into Mason jars for storage. Refrigerate overnight uncovered until it solidifies before covering.
Store in the refrigerator for up to 6 months or in the freezer for longer, or use it right away.
Notes
This recipe makes about 2 cups of beef tallow. You can easily scale the ratios up or down depending on how much you want to make.
Cold fat is much easier to chop. Chop up, then food process, which makes it much easier. You can chill it again before processing. You don't want any large chunks.
Keep an eye on the heat. If the heat on the stove gets too hot, the fat can splatter. Rendering the fat should be done low and slow.
**If the fat is too cold, it will not easily go through the strainer.
I recommend using a glass or metal container for the hot fat.