adding glycerin kills lather?

[Blufuz]

Experiment Report

So one soap cycle ago, I tried this shaving soap recipe, because it looked so unusual:
- Coconut oil 25%
- castor oil 20%
- cocoa butter 15%
- Shea butter 15%
- soy wax 15%
- avocado oil 10%
NaOH:liquid 1:1.5
9% superfat

And the liquid was 50 g water, 30 g glycerin.

I was specifically curious about what the glycerin did; most of the advice I saw on the internet was not to bother adding it because glycerin is created anyway with saponification. The author of the recipe says it “helps build up a good lather”.

So I did one batch 100% water, and the other 50/30 split with glycerin in the recipe.

First observation, the glycerin reacts with the lye by forming a puck of something solid almost immediately, so you have to add the lye gradually and stirring constantly.

But finally, after 2 months, I got to try them. As a shaving soap, the 100% water did ok; it created a fairly stable foam with tight bubbles. Better than normal soap, but not quite as good as commercial dual-lye shaving soap (Proraso).

The glycerin soap took forever to buildup a decent foam, but when it did, it was quite interesting; very firm and stable, my boyfriend described it “like ricotta”.

But that “took forever” was notable, making it completely unusable as a shaving soap. When I then try to use either soap as actual hand soap, the water one does just fine, whereas the glycerin soap does not lather! Trying my best (soaking the soap for a bit, rolling it for several minutes), I get a tiny little pouf of medium bubbles, but few enough that you can count them individually.

So unless anyone has experience otherwise, I’d say definitely don’t add glycerin to soap unless you can fix the lather problem.

 

[Johnez]

Hey Blufuz, this is an interesting conundrum. A lot of what I have to say comes from the perspective of being a wetshavers for about 15 years, and a soaper for only about 2 years.

I have to say I've not experienced a lathering issue with glycerin being the root cause, and I put a higher percentage. However I will also point out that shave soaps as a whole tend to take longer to lather and on top of that there is a precarious balance one has to maintain with regards to water additions. I recommend checking out mantic59 or any of the wetshavers on YouTube to see how wetshavers do it. You don't want big fluffy lather like Barbasol out of a can, you want tighter smoother creamy lather. Looks a bit like yogurt, wet looking and almost about to be slightly drippy. Some of the best shave soaps take a LONG time to build a perfect lather, nothing like bath soap lol.

Now, for the recipe I ran it through SMF, a screenshot:

I will say, it's an interesting recipe however I don't think it's an ideal recipe. I'll limit the criticism to the Stearic+Palmitic number-its very low. Most recommend 50 at the least. I think part of this is because "Soy Wax" is assumed to have a very high amount of Stearic Acid, and unfortunately calculators have also made that assumption. @Mobjack Bay and @earlene have sussed out the true fatty acid numbers and sap numbers:

Unfortunately replacing soy wax with stearic acid won't raise the SA+PA number enough alone, however if you did that while lowering castor to 10%, coconut to 15% and filled the balance with stearic acid (at 35%) you'll have enough SA+PA at 54% for shave soap. SA+PA is necessary for strong, creamy, stable lather.

Now I'm sorry that this really meandered off the original glycerin issue, but I'm fairly certain that if you address the stearic+palmitic numbers and adjust what you're looking for you'll end up with a great shave soap. I'd also like to add that you don't need to take away water when adding glycerin.

 

[Blufuz]

thank you for your expertise! How long is “a long time” for a good shaving soap? Doesn’t it sometimes become absolutely unpractical?

I used as a benchmark Proraso shaving soap, rather than the stuff from a can. Yes it took a little time to build a lather, but it matched what I saw in a YouTube tutorial. Instead the recipe I tried took maybe five minutes of brushing, and still yielded much less foam.

Could it be then that it was because I discounted so much water?

How much glycerin do you usually add, and what effect does it have that makes it worth it?

I admit, I am less interested in actually achieving a shaving soap, and more using it as an opportunity to better understand soap making
Your reply has been super helpful!

 

[Johnez]

5 minutes is definitely too long. Beginning to end it takes me about a minute and a half to two minutes. I'll time it next time

The water discount may have factored in. I think the lack of stearic and palmitic acids plays more into what's going on though. I have added up to 12.5 grams in a hundred gram batch, I generally generally hover around 10 grams. I keep glycerin with the fats, heating all of them together. That much glycerin in my experience loosens up the batter which helps with working with stearic acid.

 

[Blufuz]

The water discount may have factored in. I think the lack of stearic and palmitic acids plays more into what's going on though.

The lack of stearic acid may explain why neither soap matched up to the commercial one, but it wouldn’t explain the difference between the 100% water and glycerin soap

Next time, I will also try and add the glycerin to the oils; it was a pain when added to the water