Soap from fryer oil

IMPORTANT: The contents of this post are NOT intended as a tutorial so do not contain a soap recipe. They are a record of my own experiences. I take no responsibility for any soap related mishaps readers might have after having read this post! 

I’m not going to lie – I love our deep fat fryer. It’s a guilty pleasure of mine. Proper chips.

That said, it uses a lot of oil. Much as I half-heartedly justify the extravagence as preventing me from driving to pick up a take-away, I do feel bad about the quantity of oil it eats through. Being honest, we don’t actually use it that often, but I still can’t get over the 5 litre bottles we have to pour into it – bottles which would last us at least 6 months otherwise! And that’s with using oil as a butter replacement in pastry and cakes!

Anyway, with the local recycling centres closed due to Covid 19, I’ve been trying to come up with ideas for the used oil that’s currently in our house. We’d been meaning to take the bottle to the tip for ages, but never got around to doing it and now, for obvious reasons, we can’t.

I’ve read a lot of lovely posts about how to turn used cooking oil into candles, but as we have an enormous supply of these, inherited from my mother in law, it hardly seems like a useful way to employ this resource.

One thing I have done in the past, however, which needed a lot of oil/fat is soap making.

I’ve made soap from all sorts of different fats before now – lard, beef dripping, coconut oil, beeswax… All of them have been a success. As it’s a waste product I’m using anyway, all I have to lose is a little water and some caustic soda.

TLDR: We have a lot of waste sunflower oil. I’m going to use it for soap.

First of all, I filtered the oil.


You can really see in the above picture just how much… material… there is in the unfiltered oil on the right. After filtering, there was still a slight pong of chips so I went up to the bathroom cabinet and selected some essentail oils. Usually the soap-making process does away with any of an oil’s natural scent – this was especially surprising when I used lard –  but just in case, I chose rose wood, cedar wood and grapefruit oils. I didn’t actually buy there specially for soap making – I use the cedar wood to keep moths out of my clothes, picked up the rose wood by mistake in an effort to buy cedar wood, and I use the grapefruit to scent my cleaning vinegar. If you don’t have any essentail oils to hand, you could hypothetically use a perfume, but only add these lovely smells at the end of the process – just before you’re due to pour the soap into a mould.

Anyway, where was I?

After I had filtered the oil and knew how much I had, I weighed it using the Husband’s coffee scales. To do so, I zeroed the scales with a bowl on them, then added the oil. It’s really important to be accurate when making soap – right down to the gram. Once I knew how much oil I had, I entered the quantity into SoapCalc. This is an absolutely incredible online resource which tells you how my lye (or caustic soda) you need to make soap from your chosen types and volumes of oil.

The method is fairly simple. Obviously, your recipe will be completely different to the one that this tutorial details, but the order in which you do things is exactly the same.

Personally, I don’t use plain water with my lye – I use a mixture of ice cubes and water so that it doesn’t take too long to cool down. Also, just to reiterate I ALWAYS ADD THE LYE TO THE WATER. I once did it wrong and nearly melted my kitchen, so take it from me – DON’T DO IT. I am also much too impatient to wait for the lye solution to cool so… yeah. It’s a pretty fast process when I do it…


Anyway… moving swiftly on. When the soap mixture reached ‘trace’, I added my fragrance and poured the mixture into my mould. This isn’t technically a soap mould – it’s a square bit of polystyrene packaging which I really like to use because it insulates the soap in addition to shaping it. Win-win all round.


After I’d done that, and simply because I could, I sprinkled a load of dried flower parts on top – some lavender, and some rose petals, as well as some tiny little white blossoms that I don’t know the name of…


After this, as per the video, the soap needed keeping cosy, so I used an old selection box insert – left over from Christmas and which I sometimes use as a soap mould – as a lid and wrapped the whole thing in a towel to sit in my bathroom over night.


Interestingly, the soap was still soft when I got up the next morning. I mean, it wasn’t liquid, but it wasn’t hard soap, either. I guess the best comparison would be the texture of warm toffee – pliable. I tried to cut into it and internally, it looked almost crystalised. I don’t know if this was because I used only one sort of fat (where usually I use a mixture) or because it was entirely oil based. People have said on various forums that olive-oil soap tends to take longer to set so I removed it from the mould and placed it on top of my freezer in the open air in an effort to dry it out somewhat…

A few days later and the soap remained the same ‘chewy’ consistency so I consulted a book about soap making. Apparently, the caustic soda I used in this batch wasn’t of a particularly high quality (not my usual brand on account of Covid 19) and leaving the soap around 3 weeks longer than usual – 9 weeks in total – will leave me with bars which have a higher fat content than those I’m used to. This is no bad thing – hopefully it’ll make the soap more moisturising for my youngest child’s somewhat fussy skin.

Despite the obvious setback, I’m really pleased with how this turned out. Obviously, in this instance, I didn’t use a lot of oil – around half a litre – , but I still got a lot of soap out of it (or will do, when it finally sets). Whilst I can use some of the fryer oil in this way going forward, it won’t be something I can do with all of the spent fat.

But oh-my-goodness it’s such a cheap way to get soap!

I’ll send you an update on how the soap is doing when it has finished ‘curing’ in 9 weeks’ time!

Do you have any suggestions for what I could do with the next batch of oil? I would absolutely love to hear them, either here, or on Twitter.


6 Replies to “Soap from fryer oil”

  1. There’s actually a method of filtering used cooking oil, using water and the freezer, that’s way more effective than anything else I ever tried. No more weird smells! I’ll try to find it again so I can leave a link, but maybe someone else knows what I’m talking about and will beat me to it.


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