Vinegar instead of sodium lactate

topofmurrayhill · Dec 29, 2015

The effects of sodium lactate on soap have been known for a long time. Old literature suggests it was considered to be a way of using softer, cheaper oils and still getting a hard soap that cleans well. Interestingly, this literature always seems to reference both sodium lactate AND sodium acetate as being effective. The latter is supposed to have a similar effect.

To me, this suggests a fun experiment. To try sodium acetate in place of lactate, all we need is white vinegar in the lye water (if you even need any extra water) and additional sodium hydroxide to react with the acetic acid.

Let's say we have 1000 g oil and want to try sodium acetate as 2% of the oil amount, in baker's measure. We need 20 g sodium acetate, which we get from 12 g acetic acid and 8 g sodium hydroxide. Assuming typical white vinegar is 5% acetic acid, we need 240 g vinegar. This will also bring 228 g water to the party.

I want to try a small test batch after New Year's. If anyone gets motivated to run off and do it before me, the numbers should be double checked. I think I have it right with the molar ratios.

ngian · Jan 1, 2016

I have read before (I think from Susie) that sodium acetate will give soap almost the same (or lesser) power as sodium citrate and that is binding the metal ions that a hard water has.

Does it also hardens?

The Efficacious Gentleman · Jan 1, 2016

I would be interested in the effects of it on HP, if it helps with the pour - as SL is like hens teeth over here.

topofmurrayhill · Jan 1, 2016

ngian said:
I have read before (I think from Susie) that sodium acetate will give soap almost the same (or lesser) power as sodium citrate and that is binding the metal ions that a hard water has.

Does it also hardens?

I have not heard that sodium acetate is a chelator like sodium citrate, but it might be. I was looking at old soapmaking information and patents that discuss sodium lactate as a soap hardener. That is something we commonly use, but those sources all talked about sodium acetate doing the same thing.

So yes, it seems that it does harden soap, but I have not noticed that anyone uses it for that purpose these days. As crafters we aren't really familiar with exactly how it works or whether it's useful. We would have to try it and see.

Maybe there is a reason we only use sodium lactate, but I don't know.

topofmurrayhill · Jan 1, 2016

Let me just mention that y'all might want to let me try this first unless you're as bold or dumb as I am. The safety aspects are murky.

It will involve adding sodium hydroxide to slightly diluted white vinegar. The dissociation of sodium hydroxide in water is exothermic, as we know -- it liberates heat. I think the reaction with acetic acid to form sodium acetate is exothermic also and will add some heat to the solution. Not enough, I think, to be of concern as I'm not aiming for a high concentration.

Of slightly greater concern is that there would be a small amount of sodium carbonate present as an impurity. It will also react to form sodium acetate, but will release CO2 in the process. Hopefully, not enough to be a problem.

I will be doing it in a workshop rather than a kitchen. I'll have a lab coat, goggles and gloves. Most importantly, I'll be ready to run.

Susie · Jan 1, 2016

I am going to leave that experiment up to you, TOMH. My math skills lack...as does my running ability. Do keep us posted, though?

ngian · Jan 2, 2016

I guess for the experiment to be fair, it would be better if you made two small soaps, that their only difference would be the acetic acid in one & the lactic acid in the other and test their physical hardness at the same curing time.