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Making homemade soap from lamb fat!

At work recently, we cooked up 3,000 lamb shanks (yes that was three thousand- and it took us a week!) for a feast which gave a us a huge amount of unwanted fat.

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.

The ingredients:

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)

The method:

I use a commercial drain cleaner found in the cleaning isle in the local supermarket for the NaOH part of the ingredients list. Lye, which is the name for the alkali usually used in soap making was made by pouring water through wood ash (from the fire) over and over until the alkali leached out and the water became alkaline. The problem with that is unless you can test the pH (potential hydrogen) level then you wont know how strong it is or how much to put into your fat to get a soap.

Carefully weigh your caustic soda wearing gloves and add it slowly to the water in a glass bowl. Caustic soda will react with some metals. If you add the water to the soda in the bottom of a bowl - it "volcano's". Not good. Always add the caustic to the water - slowly and carefully.

Stir with a wooden spoon you will never use for cooking again with the windows and doors wide open. This fumes badly for a while and when you get a whiff you will gag and choke.

Gently stir until clear. The soda and water bowl will get hot - so be careful. Its called a thermodynamic reaction.

Melt (not boil) your 1kg of fat in a pot.

The idea is to have the fat and the caustic soda solution at roughly the same temperature - I try for around a 5 degree difference. Its easier to heat the fat than to cool the pot in the sink with some cold water. The caustic solution will start dropping in temperature suddenly as the reaction stops so you will be trying to drop the fat temperature as fast as the caustic cools - its easier to heat the fat quickly than to drop the fat temperature. I find my caustic solution usually peaks about 70 degrees and then drops quite rapidly.

Add the fat to the caustic soda solution when they are roughly the same temperature. - Be VERY careful not to splash any. It will mark your benches, make your skin itch or burn and goodness knows what else. You have a very alkaline mixture and like its opposite, acid, it can be very destructive at this point.

Pop in your stick mixer (you will have to wash this very thoroughly if you use it for food again) and blend it without any splashing until a "trace" is reached. Trace is hard to explain until you see it. Trace basically means its like custard. If you turn the mixer off and raise it up - the drips will leave marks in the surface. You should be able to make trails in the mixture with the mixer (when its off, don't splash this stuff on anything)
The orange colour of the solution will still make a white soap by the way!
Generally I find this quicker (5-7 mins) to trace than Olive oil. (Up to 20 mins)

Once you have your trace, add the essential oil, colourings and any additives like rolled oats, lavender head or ground cloves. Mix again for a minute or two to make sure its all incorporated in evenly.
I have found that leaves, herbs and flowers leave a brown ring around each particle that you may not find attractive later - you may need to experiment with a batch to see what each additive does.

I use 1 litre milk containers to make my bars in - carefully ladle the newly created soap into it.

I have been putting in any extra to my old silicon muffin tray.
I popped a bit of rolled oats in the bottom thinking it would be a bit of a scrub and soap in one but I think the rolled oats are too big. Maybe crushed oats, oat meal or even poppy seeds would be better

The mixture will stay hot for quite sometime, but will start to set much quicker than Olive oil soap. I find I can move the containers of hot soap after about an hour and a half and they seem quite solid.

I usually leave mine on the kitchen bench where I can monitor them and after 36 - 48 hours I can cut mine.

Rip the milk carton off it being careful not to handle it too much or to dent your soap. It will be firm enough to cut (don't wait too long otherwise you will have trouble getting the slices you want) but not cured enough to use.

I start by cutting off the rough ends
Then cutting the block in half and then keep halving it until I have the size slices I want.

If you use a rectangle one litre milk container you will get a slice almost the same size as a commercial bar. If you use the square base you can cut larger bars into smaller bars - or triangles! The sky is your limit!
See in this picture the uncured soap in the middle of the bar...? It does all go white eventually.

All sliced and ready to cure

These are clove powder and cinnamon coloured and scented muffin shapes out of their molds.

Soap making is not really something I would do with "little kids". As parents you all know your child's capacity but be careful - it looks like cooking but certainly doesn't taste like it! Alkaline burns can be quite serious and there is a reason this stuff clears drains.

Leave your soap somewhere undisturbed to cure for a few weeks. The saponification will still be happening and if you use it too soon - you may end up burnt or itchy because not all the alkali has been neutralised by the fat yet. I have read recommendations that 4-6 weeks is about the right time.

Making soap is fun and easy - just be careful!

I made a few batches with some friends and we had a ball - they all agreed that even though it smelt of "something" they wouldn't have picked it as "meat soap". So if you wanted to make it plain, it will probably be ok.

If you want to mix in other fats and oils - have a look at this soap calculator here at MMS. It will tell you how much water and lye to use when you put in the oil/fat types and quantities. (It uses grams not kilos btw!)

If you are worried about using the soap too soon - have a look at this link about testing the pH of soaps. However - Neutral seems unrealistic. I have tested commercial soaps and found them to be a pH of around 10. I was a bit worried and did a bit more research. It would seem that you need soap to be alkaline to work. Its the alkaline working on the organic matter that make soap work. If you made a neutral bar (like "Dove" brand beauty bars are) then it wont actually clean any organic matter like fat, grease and sweat off anything, any better than water will! For a better understanding of pH and household cleaners - have a look here

For another overview of how soap can be made from fat, have a look at Frugal Kiwis sheep tallow soap making adventure! 

Traditional and commercial soaps are made from the left overs of the slaughter industries. If you have a look at the ingredient list and find anything with tallow in it - that's gonna be animal fat of some sort. Oil based soaps are vegetarian/vegan and have been around for just as long. Detergent on other other hand is made from the waste products of the petroleum industry!!! That includes most liquid soaps. It would seem that to be clean - we need some sort of harsh chemical... to dissolve or unstick the dirt. Want to know more? - here is a potted history of soap!

Have fun and let me know how you went!
Score card:
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!
Fun -ness: Awesome fun!!!  Do it with some friends and share the different soaps when its all done!


Kathryn Ray said…
It's pretty crazy to think that something you use to wash yourself goes thru such a caustic state.

Soapmaking has been on my "give it a try, once" list for a while. Thanks for the step-by-step.
Practical Frog said…
I had quite a few problems with the concept for a while too! It like cake making. You wouldnt eat the ingrediants seperatly but mixed together and baked - yummo! Soaps the samr I think. Individual ingrediants wont do much but mixed together is where the magic is!
Let me know how you go - its really easy! - K xx
Barbara Good said…
Wow, i've just learnt a lot about soap I didn't know already. Not sure soap making is for me, certainly not with curious little hands around! Perhaps I'll stick to buying home made soaps at markets.
Practical Frog said…
Hand made soap from the markets is where I usually get mine from too! This is probably a big one off project for me, I suspect... Although it is addictive! - K xx
Unknown said…
This is awesome! I've always wanted to make my own soap.
Will a normal electric whisk work to mix the caustic soda and fat?
And how exactly am I to sieve the fat? When melting tail fat before, I noticed that not all of it melted-there were some parts that kinda dried up and became hard-is that what I'm meant to sieve?
Thank you in advance!
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