'Kyen' is high oil-content agarwood. The phase the wood must undergo before progressing to either high-resin or… even higher oil-content wood. The stage of kyen formation entails the wood has already turned brown (or green, or yellow, depending on the species) and is replete with essential oil. At the opposite ends of the kyen spectrum you have either white, low-oil content wood, widely referred to by such terms as 'oil-grade', 'low-grade', 'kayu minyak', etc; and higher-resin, lower-oil content wood ('seah'), which we call 'incense-grade', 'double super', etc. For a quick visual demonstration, compare the picture
@AZsmell posted to the one
@Oud Learner shared previously. Notice the kyen striations have progressed to a darker resinous shell. This is the type of wood that would progress to become what we call 'super king', i.e. wood that is practically only resin (very low oil) and can be carved into beads, miniatures and other artifacts.
So far as distillation, kyen is the artisanal distiller's best friend and ideal raw material. It contains more oil than resin, hence the yield is excellent, the degree of 'insanity' required to distill it minimal, and the overall profile of the oil first rate. There are some notable exceptions to this, and we've touched on them before on some of the early pages of the "Let's Talk Oud" thread. Certain types of kyen are ranked as superior to even the blackest seah. On low heat, they yield a richer profile. As a general rule, kyen requires low heat to give off scent at all, while seah requires high heat. Put kyen on high heat, and you get the scent of firewood and burning oil. Put seah on low heat, and you get almost no aroma. Seah is very difficult to distill due to the higher-resin, lower-oil content – unless of course you employ solvent extraction such as CO2, butane etc, or bathe the material in certain chemicals prior to distillation. Ethanol is also a viable extraction method (see my Oud Resin page for more details).
The overall shortage of seah worldwide has led to a situation where kyen is being collected and carved as the new chen xiang. Kyen can be wild or cultivated, and is a phenomenon that occurs in all agarwood trees, irrespective of origin. The age of infection bit is tricky because even kyara, as discussed previously, is just another type of kyen (more oil, less resin). Generally speaking, you can end up with small patches of kyen anywhere between 3-5 years after infection, and it can take up to 7-10 years for the first layer of seah to form around the circumference of the trauma. There are some lovely types of kyen harvested from centennial trees, and I would classify the
@AZsmell piece to be of the latter type.