We recently had some beef brisket, and very tasty it was too. It also produced a good quantity of tallow, which I saved. Unfortunately, I've now made as many chips as I'm going to with this year's potatoes, so I don't have a use for that much tallow in the foreseeable future. Fortunately, tallow keeps very well, provided it's clean. I don't mind
dirtytallow, i.e. with a little meat juice mixed in, for cooking, it just adds to the flavour, but that won't store well.
I looked up how to clean tallow, and it's not complicated. The fat should be melted in water, then the whole lot allowed to cool. The fat rises to the top, leaving everything else to sink to the bottom in the water. If necessary, this process can be repeated several times.
As soon as it was all melted I poured it into the Pyrex pudding basin that I usually use for stock (transparent, so easy to see how thick the layer of fat is at the top, should you be interested). I had intended to let it cool and set before separating fat from water, but it occurred to me that this wasn't necessary. The two liquids separate out well before the fat sets, so I could scoop out the tallow while it was still liquid.
I wanted to store it in a jar with as little surface area exposed to the air as possible. This required the fat to be liquid when it went in, so it made sense to transfer it while still liquid rather than let it set, separate from the water, then melt it again to pour into the jar. I took a small ladle (yes, it could be said that having a choice of ladles indicates too many kitchen implements, but it was handy on this occasion) and scooped out most of the fat into a jar. The last bit was too difficult to get out without mixing it up with the water, so I left that to set. Once set, I lifted the solid layer off, scraped the underside of anything that wasn't clean yellow fat, and broke it into a (clean, dry) pan to melt again, so I could pour into the jar.
I now have a jar full of beautiful clean tallow, which I hope will keep for most of the year until I need it for chip-making again.
Oh, and the coating of fat left in the pan after pouring? I used that to fry onions for making bolognaise sauce.
*Fat from lamb and mutton is also called tallow, whereas fat from pork and bacon is lard, and I don't know about poultry or game. Come to think of it, there's probably not enough fat on game to warrant a name for it.