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A hemiparasitic tree whose roots cling to the roots of other plants to live. Thirty years or more before the core holds enough oil. Two numbers in an ISO standard: 41 to 55 percent alpha santalol, 16 to 24 percent beta santalol. Sandalwood is measured in time and in molecules.

Heartwood and Sapwood

A cross section of a sandalwood trunk shows two zones. The outer layer is sapwood, pale and almost scentless. The inner part is heartwood, darker, where the oil accumulates over the years. Sandalwood oil is distilled from heartwood and roots; sapwood does not yield oil of useful quality.

This shapes the whole economy of sandalwood. A young tree can have a thick trunk and a thin core. For Santalum album the tree needs thirty years or more before its heartwood holds enough oil for commercial production, and trees sixty to eighty years old give the most valued wood. No fertiliser or machine shortens that time.

The tree also has an uncommon biology. Sandalwood is a hemiparasite: its roots attach to the roots of a host plant through structures called haustoria, drawing extra water and nutrients. A sandalwood plantation therefore has to grow host plants alongside the sandalwood itself.

Time, host plants and heartwood: these three conditions explain why sandalwood is at once one of the most classical woody materials in perfumery and one of the easiest to exhaust.

Santalum album in Southern India

The Mysore region of Karnataka, southern India, is the name most long associated with East Indian sandalwood. From 1792 sandalwood in the region was regarded as a state tree. In 1916 to 1917 the Mysore government set up a sandalwood oil distillery, which now belongs to the state owned Karnataka Soaps and Detergents Limited. Mysore Sandalwood Oil is India's geographical indication no. 29, one of the first products registered when the country's geographical indication system began.

High value and a long growing time are the two conditions that led to overharvesting. From the colonial period to the late twentieth century, wild sandalwood populations in India fell sharply. IUCN now lists Santalum album as Vulnerable. In 2001 an amendment to the Karnataka Forest Act allowed private cultivation; in 2009 the rules were simplified so growers could sell directly to state companies. Felling still requires permission from the Forest Department.

The oil of Santalum album is described as warm, deep wood, creamy and milky, with a long balsamic finish that lasts on skin for a long time. Oil stored for a few years is often preferred to fresh oil because it smells softer and rounder. Outside India, Santalum album now comes from East Timor, Sri Lanka, Indonesia and plantations in Australia.

In Indian culture sandalwood is also a ritual material, used as incense, anointing oil and forehead paste. It is the traditional base oil of Kannauj attars: flowers are distilled many times, the vapour passes through a bamboo pipe into a vessel of sandalwood oil, and the oil holds the scent.

Australian Sandalwood and the New Plantations

Western Australia has its own sandalwood species, Santalum spicatum. The tree is smaller than Santalum album and grows in arid country. Since the 1990s sandalwood in Western Australia has been grown and harvested under management, part of it run by Aboriginal communities. Output from South Australia and the Northern Territory is also growing.

The clearest difference is in the analysis. Western Australian sandalwood contains about 15 to 25 percent alpha santalol, while Santalum album has 46 to 60 percent. Beta santalol is also lower. In return Santalum spicatum carries components that Indian oil almost lacks, such as alpha bisabolol and farnesol, each at a few percent.

On a blotter that difference becomes structure. The Western Australian oil is lighter, with less depth and less cream, sitting between heart and base rather than sinking deep into the base. Santalum album oil is thicker and milkier and lasts longer. The two do not fully replace each other, but Australian sandalwood has become the option the industry encourages when a managed wood source is needed.

The Pacific has a third species, Santalum austrocaledonicum, grown in Vanuatu, New Caledonia and Fiji. Its santalol content lies between the other two, about 30 to 45 percent alpha santalol, and its scent is closer to Indian oil than to Western Australian oil.

Santalol: Measuring True Sandalwood

The smell of sandalwood comes mainly from a pair of molecules. Santalol is a sesquiterpene alcohol with two main isomers, alpha and beta. With a molecular weight of about 220 it evaporates slowly, so santalol is both scent and fixative in a formula. Its smell is described as soft wood, creamy and milky, with a long balsamic finish.

Because santalol is the marker, it becomes the measure. The ISO 3518 standard sets 41 to 55 percent alpha santalol and 16 to 24 percent beta santalol for Santalum album oil. A sample outside that range is either a different species or has been cut.

Sandalwood is among the most adulterated essential oils. Common additions include Australian sandalwood, East African sandalwood, amyris oil, bleached copaiba balsam, synthetic sandalwood terpenes, and odourless materials such as castor oil or polyethylene glycol added only for volume. A 2021 study tested six products sold as sandalwood oil: none met ISO 3518; three were amyris oil and two were synthetic blends.

The reliable check is gas chromatography with mass spectrometry, with chiral analysis where needed, reading the ratio of alpha and beta santalol. On safety, the Lê Mai library lists a maximum of 2 percent on skin for Santalum album oil, and notes a higher rate of reactions to santalol in surveys of dermatitis patients in Japan. These are facts for correct dilution, not reasons to abandon the material.

Amyris and the Mistaken Names

A Caribbean tree is sold under the name West Indian sandalwood. The name is botanically wrong. Amyris, Amyris balsamifera, belongs to the Rutaceae, the citrus family, not to the sandalwood family. It grows in the Caribbean and Central America; the main producer is Haiti, with some from the Dominican Republic, Jamaica and Venezuela.

Amyris oil is distilled from aged, resinous wood. It contains no santalol. Instead there is valerianol at about 15 to 21 percent, along with eudesmols and elemol. Its smell is recorded as warm, soft wood with a balsamic touch, used as a base note and fixative.

Amyris costs far less than sandalwood, which makes it both useful and troublesome. Useful because it gives a soft woody base at low cost. Troublesome because the similar name and the warm woody smell make it easy to sell as sandalwood or to mix into sandalwood oil. The 2021 study above found that half of the samples labelled sandalwood were in fact amyris.

There are other mistaken names. Indian bastard sandal, Erythroxylum monogynum, and East African sandalwood from the genus Osyris have both appeared in cut oils. Reading the Latin name on the label and on the analysis sheet is the first way to tell them apart.

Javanol, Ebanol and Synthetic Woods

As heartwood grew scarce, chemistry looked for molecules that smell of sandalwood without needing the tree. The first generation includes Sandela, a mixture of terpenyl cyclohexanol isomers in which only some isomers carry a clear sandalwood smell; it is dry, a little like cedar.

The next generation was built on campholenic aldehyde, a derivative of alpha pinene from turpentine. This group includes Sandalore and Ebanol from Givaudan, Polysantol from Firmenich, Bacdanol from IFF and Brahmanol from Symrise. Ebanol has a low odour threshold and a very strong creamy sandalwood smell, and it is on the list of allergens that must be labelled under EU Regulation 2023/1545. Sandalore and Polysantol are subject to IFRA restriction standards published in 2020.

Javanol is a different step. Developed by Givaudan, with a US patent filed in 1996 and granted in 1998, Javanol has two cyclopropane rings, a skeleton quite unlike santalol, yet it smells very close: creamy, milky sandalwood with a light rosy nuance and a moist wood feel. It is so strong that it is used only at very low levels. In the IFRA 51 index Javanol has no dedicated restricting standard.

Osyrol goes further still: an open chain ether alcohol with no ring at all, which still gives a light sandalwood smell. These molecules show that a woody smell does not require the tree's terpene skeleton. They cannot replace the full depth of aged Santalum album oil, but they have made the sandalwood note in modern perfume independent of felling more trees.

Thirty years for a core of wood.

A few percent of santalol to answer true or false.

The rest is the patience of the tree.