After the highest grades of wood have been put aside to be sold as incense chips, the remaining agarwood is used for distilling oud oil. But there's more to it than just boiling heaps of wood.
The first factor that governs the quality of the final oud oil is the quality of the agarwood chips used for distillation. While it is unfeasible to use the highest grades of agarwood to distill oil - lower quality, but still incense grade, wood is used to produce the highest quality of oud oils. The more infected the wood is, the more the resin in the wood that can be distilled.
The age of the tree also has its mark on the final oil. Older trees have a higher resin content, and oud resin gets better with age, much like wine.
The wood is chopped up into small pieces for
distillation, and the dust produced from 
polishing and finishing the
incense grade chips is also collected. For the hydro-distillation
method of extracting agarwood oil, this wood is then soaked in barrels
of water for some time to make it easier for the oil to come out when
heated.
This is the second factor that governs the quality and smell of the agarwood oil. Soaked for too short a period of time, the resin might not be as easy to extract from the wood. Soaked for too long, the oil will smell rotten and fecal. Expert distillers have fine-tuned this technique, and have deciphered how long a certain wood should be soaked. Indian Agallocha might be soaked for 3 months, while Cambodian Crassna might be soaked for 1 month. Even a day or two might be too much for an Indonesian Malaccensis that is being prepared for steam-distillation. Soak too long, and the agarwood oil might turn out smelling rotten!
After the soaking process is over, the wood is now
placed in large stills and cooked at precise temperatures and
pressures. This is the third factor that will affect the smell of the
oil. Some distillers, in order to save money, might cook the wood at
very high temperatures and pressures. This is in the hope of sucking
out as much of the agarwood oil in the shortest period of time
possible. This is done to cut down labour, fuel, water, and electricity
costs.
But the effect of this is clearly discernable in the yielded oil.
Pungent, burnt and harsh are some words to describe this type of oil.
Using
the traditional Indian hydro-distillation method, the wood is cooked
for several days. The best quality oil comes out first, usually in the
first 1-3 days of cooking. This is often referred to as the 'first
distillation'. After this, the wood is cooked further and the second
grade of oud is extracted.
Since hydro-distillation is more time and resource consuming, some distillers prefer to use steam distillation. Oils produced by the hydro-distillation method have a smokier character.
The type of distillation method used is the fourth factor that affects the smell of the agarwood oil.
Steam distillation entails cooking the oil under
guaged pressure using steam instead of 
boiling
water. Oil can be extracted using this technique in as little as one
day. However, setting too high a pressure can result in the precious
top notes of the oil's scent acquiring a burnt tar note, so this too
takes practice and experience.
The careful control of the pressure is the fifth factor that governs the smell of the oud oil, for steam-distilled oil.
While the traditional hydro-distillation method is commonly used in
India, Thailand and Cambodia, steam-distillation is most common in
Indonesia, but is also used in Thailand and elsewhere.
There are also other methods of extracting oud oil, like super critical CO2 extraction, but we have dealt with the two most commond methods.
After the oil has been distilled, it is filtered, sunned, and aged for a while. The more the oil is aged, the better it will smell.
These were the 'behind the scene' processes that take place to produce oud oil.
If this has intrigued you and aroused your curiosity, and you want to see what the final product smells like, remember to check out our product catalog.
