Science of homemade essential oil perfume

[Aedimus]

So I was doing research online and saw that when you make home-made perfumes and cologne, once mixing the essential oils with the alcohol or oils before you use the scent it should sit for 2 weeks to a month before using it.

 

The question I can't find an answer to was what exactly is happening in this period of time where the compound is steeping, and is there anything that can be done to speed it up (different base compound, temperatures, agitation, diffusing etc.)?

[Aedimus]

No one has any idea?

[DrP]

OK a guess - maybe the extended time is to allow the alcohol to fully extract/mix in with oils. Solvation can take some time.

 

Are you suggesting that the perfume sits AFTER the extraction of the oils or that the extraction itself takes w2eeks. I can fully see how the extraction of the oil could benefit from plenty of time to sit around.... Actually - it will probably depend on the exact product you are making, what leaves or plant material you are using as the source of the oils you are extracting. I would assume that the process for each product would become refined by the maker and you will get a feel for what timescales are best for your product, which could change depending on what solvents you use and what source material you use to extract the oils from.

 

I would say that you could do some tests - leave on for a week and one for a month and compare.

[Aedimus]

Thank you for responding.

 

You'll use either alcohol or some oil like Jojoba oil as a base for the scent, and than once the essential oils are mixed with the base, they're supposed to sit for a few weeks, and the scent will mature and actually hold onto the skin as well.

 

I'm interested in the chemical process that is occuring mostly because the extended waiting time is counter productive when making small batches, and if the scent changes after 2 weeks, testing small batches of scents until you find the right proportions becomes wasteful.

 

The goal would be to produce a process where you could combine scents, test and adjust proportions of the mix immediately, and than use the perfume within 24 hours. This is why I was wondering if for example setting the fluid in a centrifuge, or adding an additional ingredient might speed up the maturing process . I can't actually do anything unless I know the actual science on a chemical level though.

[DrP]

Heavy agitation, stirring and gently warming it through might speed it up. Once you find the perfect process for your product you can set it in stone and not change it - you may need a little trial and error for the first few batches maybe.

[Aedimus]

I'll definately do so. The idea I was investigating was more of a way of making it easy for a consumer to build their own scents and than to create a community around that. I designed a product that would make the mixing etc simple, but if the consumer doesn't achieve some sort of near instant gratification, I'm afraid it'll fall short.

FYI in case anyone cares, I also posted the question on a perfume forum called"bass notes" and found this:
Apparently the process is called "maceration"

Re: What happens during maceration?

 

As soon as you have your mix together and let it sit, chemical reactions start going on. These are mostly reversible equilibrium reactions ⇌, which are concentration dependent. Depending on your mix, you can get the following type of reactions:

Transesterifications:
Ester_11 + Water ⇌ Alcohol_1 + Acid_1
Ester_22 + Water ⇌ Alcohol_2 + Acid_2
Alcohol_1 + Acid_2 ⇌ Ester_12 + Water
Alcohol_2 + Acid_1 ⇌ Ester_21 + Water
but also:
Ethanol + Acid_1 ⇌ Ester_e1 + Water
Ethanol + Acid_2 ⇌ Ester_e2 + Water
So your esters will mix up chemically eventually. I've always been guessing that this is part of the process that makes a scent "rounder", as they say.

There are also (hemi-)acetalisations:
Aldehyde + Ethanol ⇌ Hemiacetal
Ketone + Ethanol ⇌ Hemiacetal
and subsequently
Hemiacetal + Ethanol ⇌ Acetal + Water
or sometimes intramolecularly:
Hemiacetal ⇌ Acetal + Water
Now hemiacetals will decay to ethanol and aldehyde or ketone on skin, whereas the process with the acetals is much slower. This is why some aldehydes are available as acetals. They smell often very similar to the aldehyde, but a bit sharper (to my nose at least).

As a third important example, there is the formation of imines, aka Schiff Bases or Schiff's Bases:
Aldehyde + Amine ⇌ Imine + Water
could also work for ketones
Aldehyde + Ketone ⇌ Imine + Water
Typically, the amine is methyl anthranilate (if there is some in the mix at all), it is one of the very few compounds that have contain -NH₂ group. The Imines also decay on skin. But the process is slow, so your evaporation rate is slowed down. And as always: imines of methyl anthranilate are very often strongly coloured, so if a perfume goes dark during maceration, it is because of the formation of those imines.

These processes go on, until "equilibrium is reached", i.e. the concentrations of all the reaction participants corresponds to how fast the corresponding reactions are. But attention: at equilibrium, the proportions will stay the same, but the reactions will still be going on! For the transesterification I made a calculated estimation once that the equilibrium should be reached in about three months.
Still, it is not a linear process, rather an exponential one: after one month, equilibrium could be reached at an extent of 66% (rather than 33%).

So the truth is, that whether you use naturals or synthetics, the constituents of a perfume actually are reactive and there will be chemical reactions going on. Well within the perfume, but also outside the bottle, also on and with skin. (The question is how much this affects the individual.)

[Acme]

So I was doing research online and saw that when you make home-made perfumes and cologne, once mixing the essential oils with the alcohol or oils before you use the scent it should sit for 2 weeks to a month before using it.

 

The question I can't find an answer to was what exactly is happening in this period of time where the compound is steeping, and is there anything that can be done to speed it up (different base compound, temperatures, agitation, diffusing etc.)?

Lately I have taken an interest in lichens and I ran across a species in the field that is used in perfumery. (Warning! Known to cause contact dermatitis)

 

So the lichen is Evernia prunastri, aka Oakmoss, and apparently it is used both as a fixative in perfume and it also adds a scent.

Evernia pruneastri

This species is harvested commercially in south-central Europe, and then sent to France where it is used in the manufacture of fine perfumes. The lichen acts as a fixative for other scents, and also adds a subtle herbal fragrance of its own.

Mind that my chemistry is lame, so you'll have to evaluate the following as to applicability to your situation.

 

fixative @ Wiki

A fixative is used to equalize the vapor pressures, and thus the volatilities, of the raw materials in a perfume oil, as well as to increase the tenacity.[1]

 

Natural fixatives are resinoids (benzoin, labdanum, myrrh, olibanum, storax, tolu balsam) and animal products (ambergris, castoreum, musk, and civet[2]). Synthetic fixatives include substances of low volatility (diphenylmethane, cyclopentadecanolide, ambroxide, benzyl salicylate) and virtually odorless solvents with very low vapor pressures (benzyl benzoate, diethyl phthalate, triethyl citrate).

Lichens produce numerous secondary metabolites and often these are key to identifying them using chemical spot tests. I don't know how the metabolites of Evernia prunastri correlate chemically to the above Wiki blurb, but here's a rundown:

Evernia prunastri @ Encyclopedia of Life

...Secondary metabolites: cortex with usnic acid (usually major, sometimes ± absent), atranorin, and chloroatranorin, medulla with evernic acid.; ...

Edited March 28, 2017 by Acme

[Endy0816]

I know people are 'aging' liquor more rapidly using pressure and temperature(not sure on specifics). Should be possible in perfume production to do something similar. Maybe perfume companies have developed something already that you can adapt.

[DrP]

What about some kind of autoclave then?

[StringJunky]

What about some kind of autoclave then?

A homebrewer's heat mat would be simple or ultrasonic mixer would be a better way, if initially more expensive, to preserve volatiles from evaporation.