What, exactly, is “torrefied?”
This will get a little sciency, but before we go there let's just cover the basics. We should first cover terminology. There’s a made up word that is used all the time to describe the process used to torrefy wood: “torrefacation.” It is, actually, “torrefaction” and I too am guilty of using the fake word; I did it today. It just sounds right, I know, but it isn’t.
Torrefaction is, simply put, a process of using heat to dry wood. Its intended purpose is to advance the wood to a condition similar to years of aging, but quickly so we don’t have to wait two decades to get that old guitar sound. Some people prefer the terms “thermo” or “thermo cured,” but it's the same thing and short for the technical term of “thermal modification.” That reminds me of when I "thermally modified” my G.I. Joe toys when I was a kid, but that’s another story entirely. Then there’s the term the salty repair tech might use: “roasted.” They are all names for the same thing.
So, what’s different about torrefaction and regular wood drying in a kiln? There are two main differences: temperature and atmosphere. The temperatures used in torrefaction are much higher than a kiln’s. Typically, kilns operate in the 40-120 degree celsius range, depending on wood type, desired moisture level, and time until the wood is needed. Torrefaction, on the other hand, operates in the 200-300 degree range. The atmosphere in a kiln is air, while the atmosphere for torrefaction is low or no oxygen so as to prevent spontaneous combustion of the wood. There are quite a few trade names for the device that is used to torrefy wood. There’s T-Kiln, kiln, oven, baker, thermal modifier, and my absolute favorite: The Torrefaction Reactor. Yes, that’s a real name.
What’s the difference in the processes? A kiln is meant to reduce the water content (moisture) in wood. Whereas a torrefaction reactor (yes, I’m sticking with that one), alters the wood. It does, of course, reduce the water content, but it also bleeds off resins and other compounds that are left behind in a standard kiln. Further, it breaks down one of the main components of the wood, technically called “hemicellulose.” That component can’t withstand the heat that the fibers in the wood can, so it breaks down long before any damage is done to the wood’s structure. It is that component that handles much of the water content of wood. With it gone, moisture levels drop a bit further, the wood acts aged, and something important happens- it starts to not like water.
Wood is naturally hydroscopic- it likes to take in and shed off water. Torrefaction greatly reduces that tendency by breaking down the hemicellulose- the main contributor to hygroscopicity. Technically, it becomes more hydrophobic- not liking water. That’s important because it does a few things. It stabilizes the wood, makes it lighter, and “opens it up” as if it were naturally aged. That’s also important because hydrophobic wood expands and contracts less than hygroscopic wood. Less movement means fewer cracks, finish spiderwebs, etc. So, it is more than just for that aged sound; it creates a more stable piece of material. Yes, cracks also come from bracing fighting against the contraction and expansion of the top, but note I said “fewer cracks” and not zero.
The big question is whether or not it’s worth the extra cost. The stability benefits may or may not be important to you. If you’re traveling a lot with your expensive guitar, maybe it’s worth considering for that purpose. The other elements are completely subjective. Maybe you prefer the aged sound and maybe you don’t hear any difference. Maybe you like that aged look the wood gains from the process, maybe you prefer the crisp, brighter look of non-torrefied tops. Maybe it’s a lifetime guitar and you want to watch and experience it age naturally. It’s all a personal decision and it doesn’t matter what I or anyone else thinks of your guitar. It’s your guitar. If you love it and enjoy playing it, then that is quite literally all that matters with regard to guitars.
