Lemon yogurt soap recipe

Do you want to know what happens with yogurt in soap?
And does yogurt soap need to be refrigerated?
How does this affect the soap color?
Read my experience below!

 

In one of my favorite books about soapmaking: “Milk Soapmaking” by Anne L. Watson, one recipe drew my attention: Yoghurt Parfait Soap, introduced by the following:

It’s really just a variation on the basic recipe, but my recipe testers liked it so much, I decided to feature it. During the testing, I kept getting emails: “Soap 20 was great” “I like everything about this one!”, “What in the world is in Soap 20? It’s best of all!”. No one guessed it didn’t have any luxury ingredients in it.

After such a description, it is evident I had to try it!

 

About yogurt soap

 

Yes, yogurt is not a luxury ingredient, but in the process of saponification, part of it changes to a chemical with perfect moisturizing characteristics: sodium lactate, as I will explain below.
This is the book on milk soapmaking from Anne L. Watson. It has a plenty of nice milk soap recipes (like the one that inspired this one) and explain nicely in detail the theory.

This yogurt soap recipe is very simple and without palm oil, and therefore ecological!

 

I have made some changes to it:

  • I added citrus essential oils, because I love lemon yogurt :)
  • However, citrus oils are more volatile and less stable in alkali conditions, so I added also a bit of rice bran flour as a scent fixative (any other flour or starch can be used).

 

As this was my first time making yogurt  soap, I also examined the effect of different temperatures on soap curing.

 

Usually, soap containing milk – and therefore yogurt soap -is refrigerated, because:

  • it can get quite hot as milk sugars speed the reaction and we want to avoid a soap volcano
  • the warmer the soap, the darker the color of the final soap 

 

To avoid this, lye solution temperature is kept as low as possible by freezing milk/yogurt in advance and dissolving lye in it while constantly cooling the lye jar.

Then, after pouring, soap is put in the fridge.

 

My question was – is this necessary, and how does this affect the color?

 

What happens with yogurt in soap?

 

Apart of coagulation and hydrolysis of milk proteins,

lactic acid  (one of the most prominent compounds of yogurt) reacts withsodium hydroxide, resulting in sodium lactate.

Sodium lactate is a safe food additive used for example as a taste enhancer, but what is of interest for us:

  •  it is a very effective moisturizer [1-3], because it is a part of “Natural moisturizing factor – NMF ” a set of compounds in our skin that have moisturizing role
  1. it is said that it has similar effect on skin as AHAcids, [I search for the scientific sources supporting this information]
  2. is used successfully for acne treatment [4]
  3. soapmakers love it, for at least five more reasons:
    • it helps to create hard soap bar that is easy to unmold - I do confirm, but the saponification reaction must finish first (does not work for soap left in fridge or freezer, see below)
    • in hot process it helps to keep the soap smoother and more easily swirlable (I didn’t try, so cannot confirm)
    • it should help to conserve soap (not sure what was meant by this, EDIT 11 June 2013: N.B. in the comments below says it is to make it last longer – it does not use so quickly)
    • stabilize the foam and makes it creamier - It does!!!!  (EDIT 11 June 2013: Later I thought it might be thanks to sugars in 11the yogurt, too…)
    • is supposed to adjust the Ph of soap (I have no proof on this, neither did not find yet the scientific evidence)

Looking at all the pros, there is no doubt the testers of Anne loved this soap!

 

Well, and I do love it too!!!

 

I never had a soap which makes such an excellent lather, one has an impression to be washing with a cream! And moreover – thanks to the fixative I added (see the recipe below), this soap smells fresh citrusy and it is literally the thing that wakes me up in the morning shower!

 

Lemon yogurt soap recipe

 

15.9 oz (450g) coconut oil
21.2 oz (600g)olive oil

6 oz (174g) white yogurt
7.8 oz (220g) distilled water

5.46 oz (155g) NaOH

0.21 oz (6g) EO lemon
0.32 oz (9g) EO litsea cubeba
0.18 oz (5g) EO lemongrass

1 TBSP  rice bran powder (or cornstarch or flour) – the scent fixative

 

Instructions

 

1) Mix well white yogurt with the water and freeze.

2) Place the lye container to the a sink full of very cold water and ice and pour in the frozen yogurt+water

3) Very slowly – in small batches – add the NaOH into the frozen yogurt/water, while constantly stirring. Control the temperature of the solution so that it does not exceed 40°C (104°F), otherwise the milk sugars will caramelize and this will impair the whiteness of the soap.

It took me 15 minutes to dissolve all the NaOH and despite this, my solution finished a bit yellowish.

4) Melt coconut oil and pour it into olive oil. This will keep the temperature of your oils low.

5) Add lye+yogurt solution to the oils and mix until trace.

6) Add to your soap a mix of essential oils with rice bran flour (or other scent fixative) and stir well

7) Finally, pour in the molds – individual preferably – in order to keep the temperature and consequently the yellow color low.

 

To freeze or not to freeze? That is the question!

 

My question was – is freezing soap necessary, and how does this affect the color?

 

I poured soaps into individual plastic molds and one plastic log mold. I covered the top of the soap by baking paper to prevent soda ash.

 

Lemon yogurt soap - 1

I put:

  • three molds into the freezer over night and in the morning placed them in the fridge
  • the log mold and one individual mold were put directly in the fridge and
  • the rest of the individual molds were left at the room temperature

I wanted to know, how the curing temperature affects the soap color.

Experiment results

 

  • Soaps from the freezer (12 hours in the freezer, 12 hours in the fridge) were the whitest – although still yellowish – were also easy to unmold, BUT! after the soap reached the room temperature, they were very soft. I damaged them a bit by manipulation – like if it was cold butter. This was probably because the saponification reaction slowed down substantially at such low temperatures – this theory was later confirmed by the fact, that 24 hours after unmolding, each soap from this batch developed a strong layer of soda ash (by the reaction of unreacted lye with air).
  • Soaps from the fridge (24 hours) were more yellow, but difficult to unmold – I had to put them in the freezer for 30 minutes. These were substantially harder than the soaps from the freezer. 24hours after unmolding, a thin layer of soda ash developed.
  • Room temperature soaps (24 hours) were the darkest and also had to be put in the freezer for better unmolding. There was no sign of soda ash 24 hours after unmolding – the saponification has taken place almost completely.
Lemon yogurt soap experiment
Soaps after 24 hours in molds – top soaps are from the freezer – see how soft they were and how they were damaged b manipulation; middle row and first from the left in the bottom row – soaps from the fridge; bottom row – three soaps on the right – room temperature. The color differences are not seen well at the photo.
Lemon Yogurt Soap experiment 2
Soaps 24 hours after unmolding. Bottom row – freezer soaps (see they are lighter, but with soda ash), middle row and first soap from right on the top- soaps from the fridge, top row three soaps from left side – room temperature soaps..

I tried this recipe in 100% olive oil variant and it works, too :)

PS: Do you like my experience? How do you make your soap?

Answer by leaving a comment below the post!

Have a nice soapmaking day!

Evik

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References
[1] E. J. CLAR, C. P. HER and C. G. STURELLE. Skin impedance and moisturization. J. Soc. Cosmet. Chem. 26 337-353 (1975)
[2] Middleton JD: Sodium lactate as a moisturizer. Cosmetics and Toiletries 93: 85-86, 1978.
[3] Harding, CR, Bartolone, J and Rawlings, AV. Effects of natural moisturizing factor and lactic acid isomers on skin function. In: Loden, M and Maibach, HI, editors. Dry Skin and Moisturizers: Chemistry and Function. Boca Raton: CRC Press, 2000. p.229-241.
[2] Garg T, Ramam M, Pasricha JS, Verma KK. Long term topical application of lactic acid/lactate lotion as a preventive treatment for acne vulgaris. Indian J Dermatol Venereol Leprol [serial online] 2002 [cited 2012 Jul 8];68:137-9. Available from: http://www.ijdvl.com/text.asp?2002/68/3/137/12541