Place the Beef Trimmings into a large pot and simmer the trimmings for 2-3 hours while stirring the fat every 30 minutes until the fat is completely rendered. The remaining fat should be golden brown. If you are sensitive to fried grease smells in your home, and can do it, render the fat outside.
Remove the pot from the heat source and let it cool for 10-15 minutes, or until the rendered fat is cool enough it will not burn you.
Strain the contents of the pot into a large bowl. This is to remove the large solid pieces only.
Place either a single sheet of paper towels, or a coffee filter, into a strainer to form a filter1
Pour the contents of the large bowl into the filter you made in the previous step so the liquid drains onto your storage container. Should any fine particles make it into the storage container repeat this step again.
The tallow should last 3-4 months.