LS paste solubility

[Sapo]

Is LS paste solubility affected by distilled h2o temperature?

I diluted paste in a closed jar, intentionally adding too little water. Then I pressure cooked the same LS paste in a closed jar for 45mins at 15 PSI. That is 121˙C/250˙F - to see if more of the paste would dissolve with higher temperatures.

The paste did not appear to dissolve further. The only thing I appear to have achieved is make sterile undiluted soap :mrgreen:.

So... are we using heat to dilute just to soften it up and hasten the process, or are we actually increasing the amount of paste dissolved per mililiter of water due to increased solubility in higher temperature water (obviously my test indicates that solubility is unaffected by temperature, but I don't trust myself as a source)?

If the solubility does increase with temperature, wouldn't the soap come out of emulsion as it cooled and blobbed up again? Basically like a strong sucrose syrup would precipitate out if cooled?

 

[Susie]

Heat softens the paste to hasten the process.

Too little water added to soap paste will result in lumps or a skin.

 

[DeeAnna]

Soap does not have a tidy predictable pattern of solubility due to its complicated chemical nature. What patterns there are will vary greatly with the fatty acids in the soap.

The best way for us to change a paste soap into a liquid soap is to add water to shift the concentration of pure soap (fats+lye) low enough by dilution to make a stable liquid form.

Speaking in a practical sense, we will not be able to force a concentrated soap paste into a liquid form by heat alone and get any useful results. Even if we could heat the paste enough for it to liquefy, the heated liquid soap will congeal back into a paste at room temperature.

Moderate heat will soften the paste as Susie says, so the paste will mix faster with the water, but it is the added water that is the key to this physical change, not the heat. If you add sufficient water but don't add heat, you will eventually get liquid soap that stays that way at room temperature. If you heat a paste soap without adding sufficient water, you won't ever get a liquid soap that stays liquid at room temperature.

I don't have data for soap made with mixed fatty acids, but I do have data for soap made with a pure fatty acid. The general trend for these pure soaps is this -

If you have a pure potassium soap paste containing about 60% pure soap -- that % of pure soap is typical for the soap paste I would make -- you would need to heat the paste anywhere from 240 C to 300 C (460F to 570 F) in order to drive the paste into a liquid form. (Your pressure cooker didn't come anywhere close to that hot!)

As you add water to reduce the concentration of soap, the temperature at which the soap will liquefy drops dramatically. Most pure potassium soaps will become a stable liquid at room temperature when the concentration of pure soap in the mixture drops into the 20% to 40% range. Oleate soaps become liquid at the lower end of the range -- more water needs to be added. Myristate and laurate soaps shift from paste to liquid at the higher end of the range -- less water is needed. Pure stearate and palmitate soaps do not become truly liquid at room temperature, regardless of the amount of water added.

Most handcraft soap makers do not make pure soap, since we usually use fats that contain a mixture of fatty acids. But looking at the fatty acid profile of your recipe should give you some clues. You might expect an olive oil soap (high oleate) to need more water to become nicely pourable at room temperature. A coconut oil (high laurate, myristate) soap is likely to need much less water. And a soap made with lard, tallow, palm, or butters (high stearate, palmitate) may dilute to a stable pourable liquid, but are likely to remain cloudy to opaque.

 

[Arimara]

To be honest, I is used a stick bender on my soap paste when I diluted it. It seemed to have done the trick. :mrgreen:

 

[Koric]

Heat softens the paste to hasten the process.

Too little water added to soap paste will result in lumps or a skin.

Well, that explains that. I just finished my first batch and it developed a thin skin on top. No lumps in it, just the skin.

I did have a lot of bubbles on top so I thought that was the cause of it. That or maybe stirring to much.

 

[DeeAnna]

You can either dilute the soap, skin and all, with tiny additions of water and patience ... or you can spoon off the thickened skin and work on just diluting it alone.

 

[Susie]

Skin is nothing more than an indication that you had an adequate amount of water to dilute, but when you opened the pot, a bit of water evaporated, leaving a layer of less than adequately diluted soap on the top. I often pull the skin off, pour the diluted soap out from under it, then dilute the skin in the leftover heat and add a bit of hot water.

 

[Spice]

Skin is nothing more than an indication that you had an adequate amount of water to dilute, but when you opened the pot, a bit of water evaporated, leaving a layer of less than adequately diluted soap on the top. I often pull the skin off, pour the diluted soap out from under it, then dilute the skin in the leftover heat and add a bit of hot water.

Cant the skin be left in the pot and just add a bit more water?

 

[Susie]

Of course, but you need to at least move it to the side to get the liquid out from under it. I either poke it into the jug the soap is going into, if I know that the dilution amount is perfect, or add a tiny bit of water. Either way, it just needs to be out of the way.