Monica asked me in a comment to my Yogurt lemon soap for fresh morning:

What about using whey left after making cheese as a substitute for yoghurt? And done through hot process method.

I immediately thought about two things:

  1. I already did a whey soap, I loved it – and should definitely share the recipe – so I do just below
  2. Hot process is not a good idea for soaps containing any type of sugars (milk and derivatives – such as whey – included):
    1. this is because sugars will always turn brown if you heat them – remember how caramel is made?
    2. apart the unwanted change of colour (unless you go for brown), you will most probably have to face a dephasing problem – there will be a liquid leaking out of your soap (pretty much the same happens if soap containing sugars gels in a mold or you make it by CPOP). This is due to overheating – the water with glycerin separate from the rest of the soap. It is mainly aesthetic problem, small leaks can be discarded or eventually it soaks in, but if too extensive, the soap can be pretty ugly
    3. worse scenario is that your soap will overheat and erupt from the mold

Before I could answer, Monica did her experiment and was so kind to share her experience in comments (thank you, Monica):

I use whey as a liquid to dissolve the lye. The solution came out yellow-orange.
In first faze of boiling the soap( at low temperature of course ) the oils and lye-whey solution separated.
I taught I ruined everything but I kept on boiling and after a while it came together again .
After 4 hours of boiling I poured the soap into a big mould because it was too crumby and the colour was and still is awful. But I made peace with the idea I will throw it away but not before trying it .
And for my surprize the soap is wonderful on skin.
I never made a better soap in terms how it works on the skin.
It hydrates the skin and leaves a little humid sensation on the skin and the skin is not shiny at all contrary looks like you put some kind of powdery make up on it.
All in one I am more than happy with this soap but very unhappy with the colour.

Whey is a yellowish liquid remaining after the production of cheese or the removal of fat and casein from milk [1]. It contains vitamins (B group, panthenol, biotin and vitamin C), proteins, minerals… but mainly lactose (milk sugar). So we are better to cold process our soap when using whey. Also, to keep the soap as white as possible, we need to keep all the temperatures rather low.

Soap containing whey will have a nice creamy lather and be very very soothing – as to my and Monica’s experience.

Now let me share with you my favourite whey soap recipe, which is basically a twist to the idea of well known oat milk and honey combination ๐Ÿ™‚


700g olive oil
300g coconut oil

380g whey
141g NaOH (6% superfat)

At trace:
30g heated liquid honey
10g very finely ground oatmeal (for a very very very very gentle peeling effect)

2,5ml vanilla FO
2,5ml cinnamon EO
10 ml milk & caramel FO (don’t remember when it comes from)


Lye and oils mixture temperatures:ย  lye (40ยฐC),ย  oils (31ยฐC)



  1. Freeze the whey to cubes – mainly if you wish to have the soap as white as possible.
  2. Slowly pour your NaOH to whey cubes. It will be very slow, but will keep the temperature low. Remember, if it heats up, it will turn yellow.
  3. Stir very well – the fats in whey will turn into soap, the solution will get thicker and you cannot see if the NaOH dissolved or not.
  4. As you stir, the protein hydrolysis can produce ammoniac smell [2], so don’t panic, it’s normal.


  1. On very low heat melt the coconut oil and then mix with in the olive oil – make sure you don’t overheat the coconut oil, you want your oils to be room temperature
  2. Finely ground oatmeal and heat honey until it becomes liquid so that it can be easily poured


  1. Pour the lye/whey solution to oils while stirring. Probably you will reach the trace quickly, but do not stop stirring, just to be sure.
  2. At thick trace add the ground oatmeal and honey.
  3. Finally add your fragrance oils.
  4. Pour your soap into mold. You want to keep it at low temperature so that it does not overheat, therefore use either individual molds or a wide and shallow mold.
  5. Sprinkle with whole oatmeal. You can put it in the fridge.

My soap just after pouring. Note the colour – I was impatient so I mixed the lye pretty fast with whey. This is CP soap that passed gel phase. Imagine what HP would do!


I did not put my soap in the fridge and it passed the gel phase. There was some liquid separated, which partly soaked in. I cut it after 24 hours, although it was still a bit too soft.

Now this is the best bit – I made this soap two years ago (I always keep one soap) and it is still without a trace of oxidation!



[1] Lecturerโ€™s Handbook on whey and whey products.

[2] Robert C. Warner and R. Keith Cannan. The formation of ammonia from proteins in alkaline solution. . J. Biol. Chem. 1942, 142:725-739