RESINS: BENZOIN

It’s time to get back on track with Materials Wednesday and finish up the series on resins. I’ve written before on myrrh and mastic, but somehow missed one of the important resins, benzoin. This material is used extensively in perfume, mainly as a fixative; it is also used medicinally,  and burned as incense. In other industries, benzoin is used to enhance and fix food flavorings, especially vanilla, as a chewing-gum base, and to flavor tobacco. It is sometimes used in the manufacture of varnish.

Benzoin is the gummy resin obtained from trees in the genus Styrax, mainly Styrax tonkinensis, which grows in Southeast Asia. Benzoin is also known as “styrax” “storax” or “Siam benzoin”. The raw material is harvested in much the same way as other resins, by making cuts in the trunk of the tree, waiting until the sap runs out and solidifies, then scraping the “tears” off of the tree.

Because benzoin is an important commercial product, efforts have been made to study and improve methods for its cultivation and harvesting. There are now Styrax plantations, so benzoin is not in as much danger as some other materials that are still harvested from the wild.

The scent of benzoin resin is mildly sweet and, of course, resinous, and bears some similarity to vanilla. Because the scent is mild, it is a little hard to pick out of a perfume mix, but it does lend its own subtle signature to a blend. A lot of my perfumes contain benzoin in various concentrations.

Benzoin resin comes as a solid, which can be burned as incense or tinctured. When burned as incense, a magical transformation occurs and the smoke creates a powerful scent that is very different from the raw resin, absolute, tincture, or other preparation for use in perfumery. The beautiful, characteristic scent of benzoin used as incense is especially startling the first time you burn it, if you are used to smelling the tinctured or otherwise treated resin. It is unlike any other form of incense, and is one of my favorites.

For perfumery, benzoin can also be obtained as an “absolute”, which is generally pre-diluted with alcohol. Although this dilution makes it pourable, it is still dense and sticky, and cleanup is not fun. The hassles of working with benzoin aside, it is a useful material that I like having in my main selection of basic perfume-building blocks.

[Benzoin resin on tree trunk from Givaudan website, although it seems to be a cropped version of a photo from Accademia del Profumo, or from a website on “securing the future of benzoin in Laos”, or from some other ambiguous source. It seems to be very popular. Benzoin resin clump from an essential oil vendor’s website; Styrax trees image from an Indonesian commerce promotion website, Styrax flowers and botanical drawing from Wikipedia.]

SCENTS OF GRASS: THE CYMBOPOGONS

Last week’s materials post was on vetiver, so this week’s will continue with three related grasses that are used in perfumery and other aromatic applications, Cymbopogon citratus (lemongrass) Cymbopogon nardus (citronella) and Cymbopogon martini (palmarosa). Like vetiver, these are all in the grass family, growing as big clumps, but for the Cymbopogons, the essential oil is derived from the tops of the plants, not the roots. All of these species were probably originally native to India and/or Southeast Asia, but have become widespread throughout warm parts of the world due to culinary and agricultural uses.

Lemongrass is most commonly thought of as a food flavoring due to its extensive use in Asian cuisine. Lemongrass oil is obtained by distillation of the green parts of the plant, with most of the aroma contained in the base rather than the outer parts of the leaves. I think of lemongrass imparting a delicate flavor to Vietnamese cuisine, and working well with coconut-based curries. The essential oil contains citral, limonene, citronellol, geraniol, and many other molecules that have insecticidal properties and mosquito-repellant properties, as well as medicinal properties, especially anti-inflammatory and anti-fungal activity.

Lemongrass essential oil has a characteristic, unmistakable top to mid-range scent that can be quite heavy, strong, and overpowering if used in perfumery, so needs dosing with a light hand and with the proper accompaniments. Given that most of the lemongrass constituents, and all of the main ones, are available as pure aromachemicals (that’s for another post!) the perfumer has the option of creating a unique “lemongrass” accord to use, or choose which aspect of it to emphasize in a blend.  I used lemongrass essential oil in Kyphi, but I think if I used it in another blend I might opt for a lighter reconstruction that’s more like the flavor one gets in delicate lemongrass-flavored cuisine.

Citronella, the evil cousin of lemongrass, contains large quantities of citronellal, citronellol, geranial, limonene and other “lemony” molecules. It is an important source of these and other isolated aroma chemical molecules. Like others of its genus, it looks like a small clump of pampas grass, not a very attractive sight. Perhaps the best known use of citronella is as an insect repellant, with citronella candles traditionally burned to keep mosquitoes away from outdoor gatherings and to scent insecticidal sprays. Because of this association, in my opinion, citronella does not work well in perfumery. Who wants a perfume that smells like bug spray? Having said that, the aroma molecules obtained from citronella have a multitude of uses in perfumery, and are probably present to some degree in the majority of perfumes.

Palmarosa is yet another one of those plants that looks like pampas grass. The green part of the plant is distilled once it has flowered,, but plants can live for many years, regrowing the parts cut for distillation. The essential oil contains mostly geraniol and geranyl acetate, along with linalool, myrcene, farnesine, and ocimene. As in the case of other essential oils, the reported percent of constituents, and the constituent profile itself varies depending on whose publication you read. Apparently the composition differs depending on which part of the plant is used, and I’m sure it also varies by season, harvesting techniques, and distillation techniques. 

Palmarosa essential oil smells sort of like a mixture of rose geranium and lemongrass, not too surprising given that it’s a Cymbopogon. It seems a little sharp and raw by itself, and I have not used it in a perfume. I can see how it could work as an excellent substitute for rose geranium. However, I can’t see how it would work as a substitute for rose, although it seems that it has commonly been used to adulterate rose oil or absolute. It is reported to have antiseptic properties and to be very good for the skin, with “anti-aging” properties. I’ll have to try it in my formula.

[All plant photos are from Wikimedia; product photos are from retailers' websites. I see one of them used the Wikimedia palmarosa image in their advertising.]

MATERIALS WEDNESDAY: TOMATO LEAF ABSOLUTE

In considering raw materials, I have no plan for how I go about choosing topics. So far I’ve written about newer materials that I’m in the process of evaluating, so here’s another one in the same category. The last one was palo santo, and this one is also a green note, so I guess I could start with a series of “green” materials.

Anyone who has encountered a real live tomato plant probably knows what tomato leaves smell like. It’s a unique scent that epitomizes summer. Apparently it’s a love-it-or-hate-it scent, but for those of us who love it, wouldn’t it be nice to capture it as a perfume note? That was my hope when I got a batch of Robertet’s tomato leaf absolute, but it was only partially realized. The absolute is a viscous yellow-green liquid that smells more like generic green leaves than tomato. It’s not too sticky, so is relatively easy to work with. It's definitely green, somewhat grassy and leafy, with only a remote hint of tomato. In reality, it’s more like a milder version of violet leaf absolute than tomato.

I suppose it’s not surprising that the scent of fresh tomato leaves is hard to capture in a natural, extracted product. The scent actually comes from bulbous structures on the tips of the hair-like structures (trichomes) that cover the leaves and stems, and is secreted as an insect repellant. This secretion is what we smell when we gently rub a tomato leaf to release the fragrance.

When tomato leaves are harvested, I imagine there’s no way to separate the trichome secretion from the leaves and stems, so everything gets extracted together and the green, leafy components end up predominating. There’s nothing wrong with that, but if you’re expecting a strong and authentic freshly-rubbed tomato leaf smell, you won’t get it.

What you do get is a very strong, dark green, pungent scent at first that gradually becomes lighter and more herbal, with a hint of something almost perfumey. It’s lovely and fresh, but not all that tomato-y. I don’t detect any “off”-notes that would need to be masked, so it’s versatile and could participate in any aspect of a fragrance. It’s not even bad as a solo act. Longevity is not great, two days on paper and a few hours on skin. It would function as a top- to early middle note in a blend.

I think tomato leaf absolute could be a good starting point for reconstructing a true-to-life tomato scent, but it would take a lot of tinkering to get it right. As is, it could be used in any composition that needs a light green note, but it would not be explicitly recognizable as "tomato leaf". 

[Tomato leaf trichome image from UC Davis website; other images from Wikimedia]

TYPES OF PERFUMERY MATERIALS

Materials Wednesday: Part 1

How to start a series on perfumery raw materials? I suppose I could just dive in and consider individual materials one by one, but somehow it makes more sense to first consider materials by broad category rather than individually. I think everyone is at least vaguely aware that materials can be of different types, but may not realize the advantages and limitations of each type of raw material. So here goes with the most general classification possible.

Single Molecules. Chemically speaking, these are the simplest and most basic of all materials in that they are composed of a single type of molecule, such as phenyl ethyl acetate, amyl salicylate, or vanillin. Molecules with long, unwieldy names like (5E)-3-methylcyclopentadec-5-en-1-one are often given semi-descriptive trade names like Muscenone. Although different versions of an aroma molecule share the same chemical formula, the material itself may consist of different structural isomers (same chemical formula but different arrangement of atoms) or different stereoisomers (same formula and arrangement of atoms, but rotated in different ways). A given material may be a single isomer or a mixture of isomers, conferring different olfactory properties. The advantage of using single molecules is that the perfumer knows almost exactly what is going into the formula, common aroma chemicals are readily available in bulk, and they are usually easy to work with. For the beginning perfumer, probably the biggest down side of aroma chemicals is that there may be no real-world equivalents for their odors, so the properties of each one have to be learned from scratch.

Synthetic accords or bases. These are mixtures of aroma chemicals that, together replicate a complex natural scent such as rose, gardenia, or oud, or a fantasy scent such as “ambrosia” or “clean underwear”. Many bases of this type are available commercially as convenient ready-made components to use in perfumery. They are not the same as the “fragrance oils” that are commonly sold to hobbyists as functional scents for soap, candles, and lotions. The latter are some sort of odorant mix that approximates a complete perfume, diluted in a carrier oil, whereas perfume bases are the pure aroma chemical formula meant to be used as a building block, not a finished fragrance.

Naturals. These are the essential oils, absolutes, tinctures, and other materials derived from plants (and occasionally animals or minerals) that most self-taught perfumers start experimenting with in the beginning. The advantage of natural materials is that their names generally indicate what they will smell like, and most of them have familiar, “real-world” smells. Most natural materials consist of a large number of very different molecules that, together, produce the familiar smell, so are actually complete perfumes or accords in and of themselves. The advantage of using naturals is that they can be readily understood and easily impart complexity to a blend. The down side is that the very complexity that makes them attractive can lead to unwanted interactions and “muddying” of a blend if too many are combined in the wrong proportions. 

Another disadvantage is that naturals from different sources may smell very different, and the same material from the same supplier may smell different from batch to batch, and availability depends on crop yields, international politics, and many other unpredictable factors. A lot of naturals are difficult to work with in that they are sticky, gooey, lumpy, or otherwise nasty in consistency. They have to be melted, diluted, tinctured, or otherwise processed before they are usable, and the final formula often ends up cloudy so that it requires fining and filtering before it is clear enough to sell.

Mixed accords. These are like synthetic accords except that the desired smell has been created by combining naturals and aroma chemicals.

I think the majority of perfumers work with all of the above types of materials unless they are solidly in the all-natural category.

[All photos are from Wikimedia except for the alembic still, which is mine.]