Normally that would have been thrown into the skip but I had remembered reading somewhere that animal fat - or tallow - can be used for making soap. If you have a look on a commercial packet of soap you will see something called sodium tallowate - that's scientific speak for rendered beef fat.
I have been making my own olive oil soap for a few years now with reasonable success, so I collected up all the fat I could, rendered it and gave making soap from fat a go!
Here's what I did...
I rendered the fat, which basically involves heating it to melting point and then filtering it through sieves that get finer and finer and then adding water (don't boil the fat or adding water will make it explode) and leaving the fat to set - on top of the water. The impurities should fall to the bottom and be caught in the water - the clean fat will set on top of the water. You may have to do this several times.
1 kg rendered lamb fat
300 mls water
130gms Caustic Soda (NaOH)
20mls of essential oil
Few teaspoons or so of colouring agents (I only use herbs and spices as some commercial colourings including supermarket food colouring, seizes the soap and makes it useless)
Have fun and let me know how you went!
Green-ness: 4/5 for using a waste product - hard to 'green up' drain cleaner though...
Frugal-ness: 1-5/5 If you can scent it without spending a fortune on essential oils, it can be very frugal but if it costs you $40 for the scent - its not frugal at all!
Time cost: Rendering can take a few days. The actual soap making, maybe 20 mins. The curing, up to 6 weeks.
Skill level: As long as you are careful -its very, very easy!