Start by removing any skin, bones, and large pieces of meat. Cut the fat into large chunks.
If the fat isn't as white as you would like, soak it in ice water for about an hour.
Cut the beef suet into small cubes or grinding it up. This will help it render more quickly.
Place the fat in a large pot over medium heat and simmer it for several hours, stirring occasionally to prevent it from burning. (You can also use a slow cooker if you prefer.)
Once the fat has liquified, strain it through a cheesecloth or fine mesh strainer to remove the remaining meat and other tissues.
Pour the liquid fat into a heat-proof container and let it cool until it solidifies. (Use a wide-mouthed flexible container if you plan to further purify it.)
Purifying the tallow
To further "purify the tallow", once cooled, scrape off any remaining solids that have sunk to the bottom of the tallow. (Also scrape off the top, if necessary.)
When melting the tallow, bring it to a simmer. If a foam forms on top, allow the tallow to cool and remove the skin that forms over the surface.
Repeat the process until foam no longer forms when simmering the tallow.
Strain and pour the finished tallow it into its final storage container.
Allow the tallow to cool before covering and storing it.
Video
Notes
Storing tallow
While it is generally shelf stable, its shelf life will increase by keeping it in a cool, dry place in an air-tight container. For longer keeping, consider vacuum sealing some of your homemade tallow and keeping it in the fridge or freezer.