Chemielabor, Seife
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How to make Curd Soap: Part 1&2

Hi gals (and guys)!

I made a little video series explaining and showing how to make curd soap, or „Kernseife“, as we Germans call it. It’s a great staple to be able to make, as a soaper because you can use it in a wide variety of cleaning products. I’ll post a couple of recipes and examples of how to use curd soap in my next blog post. This one shows you the two different ways on how to make curd soap. Either from rebatch soap or from scratch.

Curd Soap from Rebatch Soap:



What you’ll need for saponifying the superfats:

500g Rebatch Soap Scraps (you need to know the %of Superfat)
(x)g NaOH/Lye

How to calculate the amount of lye you need:

Let’s take Teach’s Bastile recipe as an example. This is Cathy’s go-to soap recipe that many of my fellow soapers use as well. Cathy uses the following ingredients:
6.2% castor oil
25% coconut oil (76deg)
69.8% olive oil (pomace)
She superfats the soap at 5%.

The next step is to go to your favourite lye calculator to calculate the amount of lye you need. I’m using SoapCalc because it has the widest variety of Oils and the recipe printout is nice and well-designed.  Put in your recipe with percentages and then break out your calculator (or do it in your head): You need your weight of soap scraps (500g) and calculate 5% of that. Because 5% of your soap will be unsaponified fats&oils. Superfat at 0%. Input that amount as the complete weight of oils, like I’ve done here:

Screen Shot 2014-08-15 at 15.37.48

Then click on „calculate recipe“ and then on „view or print recipe“. Now you can see how much lye you need for 500g of soap scraps:Screen Shot 2014-08-15 at 15.38.25

It’s that easy. :)

What you’ll need for salting out the soap:

at least 6 Litres of distilled water
at least 1000g pure salt

I can’t tell you exact amounts, because it depends on the soap scraps you use.. If you’ve used soap that contains a lot of colorant and additives like clays, you’ll have to salt out more. You can see this in my video – I used soap that contains activated charcoal AND healing clay. Even though my salt solution was clear in the end (after salting out 6 times), my finished curd soap didn’t end up being white, still kind of grey-ish.
But I recommend salting out the soap at least 3 times. For each time you will need about 300g of salt and 2.5 times the weight of the soap scraps as water.


Curd Soap from Scratch:



Making curd soap is a good way to use up some fats/oils that you’ve bought in bulk but haven’t used up and now the best before has arrived. Like I had with my coconut oil – I bought a couple of Kilos a while back, but then Summer arrived and I don’t really soap in the summer. My soap recipes don’t like heat that much and turn out wonky.

So my soap recipe contained:

1000g Coconut oil (92deg)
200g NaOH/Lye (I added a couple of grams to achieve a lye excess)

And for salting out I used up:

1400g pure salt (about 450g each time)
8 litres distilled water (about 2,5l each time)

If you have any questions, ask in the comment section!

2 Kommentare

  1. Scooter sagt

    I really liked your videos. I just watched all three. I am interested in making a „savon de Marseilles“ style soap and it seems to me you are doing something similar. I know that in the ancient soap recipes the solution is boiled for days and Marseilles soap in particular is salted out and then washed.

    Can you use this to bathe or wash your hair? Or is curd soap primarily a laundry soap? Since salting out removes the glycerin I’m wondering how it would feel to wash with it. Thanks, again, for the videos.

    • curd soap is primarily used for laundry and cleaning. I have relatively sensitive skin, so I def. wouldn’t use it as a body product.

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