Lemon juice soap

One of the soap groups on Facebook that I belong to does monthly soap challenges and this month they challenged people to make a soap using lemon juice. I thought that was such a fun idea, and something I’d never done either, that I wanted to give it a try myself and show you the process and results, so you can have a go at it yourself.

One of the problems with using acids, like lemon juice, is that it will neutralise some of the lye in your recipe. The acid in lemons is citric acid, but the amount of citric acid varies between types of lemons as well as between the individual fruits themselves. So unless you’re a chemist with the right equipment, you can’t really know how much of the lye will be neutralised. If it’s too much, you’ll end up with a soft gloopy mixture because of the excess oils that didn’t get saponified (turned to soap). To make sure that doesn’t happen, you need to reduce your superfat or lye discount to a minimum. I reduced my superfat to 2%, and if I replace all the water in the lye solution with lemon juice I will get a soap with a superfat somewhere between 5% and 8%. Here’s the recipe I used:

Lemon juice soap recipe

  • 375 g olive oil
  • 25 g castor oil
  • 55 g caustic soda
  • 100 g lemon juice
  • 1 teaspoon sodium lactate
  • 15 ml lemon essential oil
  • annatto seed colourant

I pressed out three lemons to get 100 g of juice and placed it in the fridge to cool. Lemons not only contain citric acid, but also sugar, and I wanted to prevent the sugars from burning in the lye.

Once the lemon juice was cold, I carefully stirred in the caustic soda one teaspoon at a time, and check out the cool colour display I got! First it turned a bright yellow before going orange. To be on the safe side, I placed the jug in the sink with cold water to keep the lye from going too hot, and luckily it didn’t get any darker than that orange.

I continued normally using the cold process method: oils in one pot, and once the lye had cooled down, adding the lye to the oils and stirring. Because I knew from other soapers that the lemon fragrance from the juice would not come through in the soap, I added lemon essential oil to the soap,

I also decided to have a little fun with colour using annatto seed colourant, which I added to about 1/4 of the soap mixture. I then poured the colours into a bowl, alternating between the yellow and uncoloured soap, like you do in the ‘in-the-pot-swirl’ method. I gave the soap in the pot an extra swirl with my spatula and then poured it into the mold.


I had no idea what the lemon juice would do to the colour of the soap and to the soap itself. I didn’t insulate it and despite it being in a cavity mold, the soap did go through a gelling phase. So a word of caution: don’t insulate and keep the soap cool! And despite the soap looking rather dark here in the mold and the next day when I unmolded them, they did turn a lovely white and yellow marble effect after a couple of days. And testing it after nearly a week already felt that it was going to be really pleasant mild soap!

For more information and ideas, check out this blog post about adding fresh ingredients to soap!



  1. Hello Jackie, I would really like to try this recipe, but perhaps with lime juice and another base oil or mix of oils. Would you kindly share the percentages of this recipe, as well as the lye concentration (for soap calc) please?

    • Hi Bubbly! Yes you can substitute the lemon juice for lime juice. Feel free to use any soap recipe for it! I use a 2:1 ratio water to NaOH. Happy soaping!

      • Thanks Jackie — 1) do you think a greater water discount would be okay? 2) what is the percentage for the oils please, are you okay with sharing those?

      • Hi Bubbly! You can use a greater water discount, just be a aware that the less water you use, the faster the reaction will move. About the oil percentages, I have no problem sharing those, but you can work them out yourself easily: 375/400*100=93.75%. That’s the olive oil. And the remainder 100-93.75=6.25% is castor oil. Happy soaping!

    • Hi there! Yes, you can counteract the citric acid from the lemon and other citrus fruits, but I found the amount is negligible and it will just add to the superfat. It’s actually quite difficult to work out the exact amount of citric acid in the fruit you are using as the amount differs not only from species to species, but also from tree to tree and even from fruit to fruit! Technically, if you took an average of 5g citric acid in 100g juice, you would need 3g extra NaOH. This would amount to roughly 20 g extra oils in your soap. Hope this helps!

      • Thank you for the reply Jackie… I used this website to adjust the lye in my soap

        The experiment actually came out well… a coconut milk, fresh lime juice with dried lime zest. You are correct, the amount of extra lye was negligible, about 3-4g. I lowered the superfat amount in soapcalc to 3% because I knew there would be an effect on the super-fatting. The first time around the soap was a bit soft, and it is hardening up over time… the second time around with the same #3 bag of limes, I used more lime juice and added kaolin clay to get it to harden up a bit more. It actually turned out well… it feels like no soap I’ve ever used before. I call it “Jimmy Buffet” soap. πŸ™‚

  2. Hey Jackie, I made this, well I should say I experimented with the Lemon juice, and tried several different recipes and was quite astounded with the results.
    First 3 recipes were with different oils and it only worked with soft oils, it got very hard, whilst working with it, even with 10% coconut oil. When I made it with your recipe I had resounding success and could unmold my soap in under 24 hrs.
    I then tried another 2 recipes via HP, as this is my normal way of soaping, the soft oil recipe never hardened although it’s only been a few days. The hard oils, 65%, hardened although it is softer than your recipe.
    Any ideas as to why the different heat gave me different results?
    I’m looking forward to seeing how the CP soft oil soap foams up but I will give it 4 weeks.
    Before my experiments I went onto a HP Facebook and asked (something that I rarely do-being active on FB) if anyone had tried using straight Lemon Juice but no and got told that it won’t work. I will put my results up once finished and acknowledge that this came from you- Jackie from inmysoappot.co.nz. Hopefully a bit of free advertising for you πŸ™‚
    Thanks again, Julie.

    • Thanks, Julie, for writing about the issues you had with the lemon juice and other recipes. I always love hearing about other people’s experiences! I’m not really sure why your other recipes didn’t work, I can only imagine it being the heat from the sugars that sped up the chemical reaction. You’ve made me really curious, and I’m going to try it myself with a standard recipe to see what happens. I’ll update it on this page! Thanks also for sharing the info in the group! Always happy for the extra exposure πŸ˜‰ <3

      • Just a quick update. The HP soft oils took 3 days to harden and they are rock hard but have a really high pH of around 11. So weird??!!…..I feel like I’ve opened Pandora’s box and everything I’ve learnt is changing πŸ™‚

      • The citric acid in the lemon juice will have used some and reacted with the caustic soda, but then you’d expect it to be a lower pH. I’m guessing that the saponification just hasn’t completed yet, despite the cooking. Always new surprises and new things happening when you make soap! Fun!

  3. Hi Jackie and this came out superb! I have only seen this one other time and it was a complete fail, so good on you πŸ™‚
    I have soo many Lemons, I may give this a try.
    Did you ever test the pH of this soap?
    Many thanks,

    • Thanks! It turned out to be one of my best soaps ever, so do give it a try. The pH of soaps is a bit of a misleading thing and rather unnecessary. I’ll be blogging about it soon, and hopefully that will clear things up for people. Good luck with the lemons!

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