Fragrances in cold versus hot processed soap

[Homeslice]

Having watched many youtube videos, I learned that most fragrances have a "flash point", the temperature at which if you add them at that temperature or above they will quickly evaporate or steam away or whatever and you will lose the vast majority of the fragrance. So I thought, no problem, make hot processed soap, and just add them towards the end when the temperature has gone at least several degrees below the flash point.

But looking for fragrences, I see a lot of fragrances that say they stuff like: "Good is cold processed soap? Yes." But then do not mentioned hop processed soap.

So what does this all mean? Is the deal that fragrances are much, much much better used on cold processed soap than hot? Or some are? And that's even if you add them to a hot process when its cooled well below the flash point?

Thanks!!!

 

[ChemicalPyros]

Hello @Homeslice,

All fragrances/perfumes/essential oils are constituted of several molecules (unless you are using a simple molecule as a fragrance (i.e.: menthol). Those molecules that constitute the mix of the fragrance have different volatilities and of course properties. So the safest way with a fragrance is the cold process, you maintain the stability of the fragrance molecules and you avoid loosing the molecules that are highly volatile.
When you go with the hot process, you will accelerate the evaporation of the highly volatile molecules, and if there are other molecules that react with the oil or the lye or any other additive they will react more rapidly (i.e.: vanillin) or they will simply degrade. So in conclusion if you add your fragrance during the hot process it will always loose something.

There are some ways to reduce this effect, such as mixing your fragrance with kaolin (or any bentonite or hectorite powder) or starch or both at least 48 hours before soapmaking. The powder will absorb the fragrance and stabilize it against the heat, keep in mind that this method reduces the effects but does not eliminate it.

That being said, it is worthy to note that while you do not loose much of the fragrance during the cold soapmaking process, you might still loose the volatile components during the curing, especially if you will be curing for a long time.

Hope this helps

 

[Homeslice]

Got it, thank you ChemicalPyros! Let me ask one other question that might be silly. Let's say that a fragrance has a rating maximum amount that can be added to soap, call it 5%, before that soap might become an irritant. Let's say that I know that a certain amount of that fragrance I add to the hot soap (even while its a cool as possible) will be evaporated way, call it 3%. Can I thus add 8% to the soap, leaving, after the 3% evaporates away, the maximum 5% so it is not a possible irritant? Or might the 3% that evaporated away leave certain solids or something behind that could still cause irritation?

Thanks!!

 

[ChemicalPyros]

Sorry for the late reply, but usually my weekends are usually electronics free.

As for your question, the loss is not uniform molecule-wise, a fragrance contains a mixture of molecules with different volatilities, so you will loose the most volatile first and you will remain with the less volatile ones.

So quantity-wise, if you start at 8% you may be at 5% at the end of your saponification process, but from a molecular composition you will have a very different composition at the end. This may or may not be a good thing, so I'll leave it to you to decide.