Some more info about why I'm particularly interested in a torrefied shaft, edited to keep the relevant stuff, from a guitar luthier Q&A:
Q: And that’s due more to how wood changes over time rather than a case of "they don’t make ‘em like they used to?
A: Correct. Pre-war Martins did not sound the way they do now when they were fresh out of the factory. There are also some acoustic guitars being made today that are of equal or better craftsmanship than some vintage guitars but still can’t get that response.
To understand why, you need to think about what happens to the wood over time.
Freshly cut wood is mostly made of cellulose with lignin, which is a particular type of resin that holds the cellulose together. It has a fairly large content of volatiles - pitches, sugars, oils, and other chemicals that are byproducts of a living tree. It also has considerable water content.
These volatiles initially have a damping effect when a guitar is first made. They prevent the top from vibrating as freely as it could.
Over decades of air-drying, these volatiles will oxidize [combine with oxygen], gas off and mineralize. The slow chemical reaction emits a gas and leaves a mineral residue. The lignin also sets like a glue, holding the cellulose together.
Trees also have vessels within them that bring water from bottom of the trunk up through the tree. These vessels have valves. These also oxidize and mineralize, closing the valves. This changes the cellular structure of the wood from something like a sponge, which is open-cell, to something like styrofoam, which is closed-cell. This eventually makes wood more resistant to temperature and humidity changes.
Three main things happen over time as the volatiles oxidize, the lignin sets and the cells close: 1) Sound velocity is improved because of diminished damping. 2) The wood becomes lighter and vibrates more freely. 3) The wood becomes stiffer.
When wood is fully cured and volatiles are fully oxidized, it becomes a better material for musical instruments.
All these things happen naturally, but it takes decades of exposure to air for wood to fully cure. Humidification slows this down. Torrefaction speeds up that process. It changes the chemical content of the wood to make it resemble what it would be decades from now.
To add to the above, here's some interesting take on Stradivarius' wood from a NYT article, note the tidbit about moisture content in particular:
The researchers also discovered that one-third of a wood component known as hemicellulose had decomposed in Stradivari and Guarneri’s instruments. Because hemicellulose naturally absorbs a lot of moisture, the effect was that the instruments had about 25 percent less water in them than more recent models.
“This is fundamentally important because the less moisture, the more brilliant the sound,” said Joseph Nagyvary, a luthier and a professor emeritus of biochemistry at Texas A&M University who was not involved in this study.