What is Torrefied Wood? - Luthier Tips du Jour Mailbag
In this episode, Robbie O’Brien interviews Bob Lennon at Thermal Wood Canada about how wood is torrefied.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: What exactly is torrefied wood?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Italy. "Robert, there seems to be a lot of interest in torrefied wood. What exactly is it? Francisco in Italy."
Francisco in Italy, that is a very good question. Basically, it's wood that's been cooked. It's been put through a thermal process and moisture has been removed. It changes the cellular structure. The end result is it's very light and very stable. Now is that advantageous for building instruments? It could be one of those small things that gets you over the hump and makes you a great guitar instead of a good guitar. However, I've heard a few bad sounding guitars made with torrefied lumber. I've also heard some very good guitars made with lumber that wasn't torrefied. So it's not the only thing, but it could be one of those things that when all the stars align, one of those small things that makes you have a great guitar.
Now, back to your question on what exactly is this wood? Now, recently I visited a company in Canada called Thermal Wood, and they do this torrefaction process among other things at their plant. It was a very interesting visit I had, and I had my camera rolling. So let's go talk to the people there at Thermal Wood and see how this process is done.
Thermal Wood Canada interview with Bob Lennon
Okay, here we go. Robert O'Brien again. I'm here at Thermal Wood Canada. I'm here with Bob Lennon. Bob, thank you very much for your time.
Bob Lennon: Thank you very much.
Robert: And this is the oven here behind us. This is where the wood goes in and gets cooked and Bob's going to walk us through the process.
Our torrefaction process
Bob: Well, the process is basically is that our oven takes 14,000 board feet in one shot through the process. What we do is we prepare it. As you see the wood behind us here, it's prepared at two inches thick. So we take two four quarter boards, slap them on top of each other, and then we stick her in at every 12 inches in between.
The reason why we do that is that the process works basically is that our heat source comes from propane. We transfer the propane heat from the flame through a thermal oil that we pump into a radiator in the back of the oven. There's a large fan there that basically flows it through horizontally in a clockwise fashion. So if you see here the door, there's a section over in the side where we got the same section there. The wood fits in directly into the oven in that side, and then in the back end, the fan blows the air through the radiator. It comes up this side and then it flows through the wood like a filter, and then it just keeps on going around. The only thing that we use inside the oven for the process is heat and steam. The reason why the steam is there-
Robert: No vacuum, no pressure, none of that?
Bob: There's no vacuum, no pressure, no. We use the steam to basically remove the oxygen in here because we go to temperatures of 200 degrees Celsius, which is 400, almost 500 degrees Fahrenheit.
Robert: That warm?
Bob: Very, very close to sparking. So if you had any oxygen whatsoever in the air, you'd-
Robert: So the steam removes the oxygen from the air.
Bob: The steam removes the oxygen from the air.
Robert: Okay.
Bob: This wood that's in here is going in for the music grade as I mentioned a while ago. It will go in-
Robert: Back, sides, necks?
Bob: Back, sides, necks all the way through. It's bird's-eye maple, curly maple that's in there. The process can do any species of wood. The difference is that the amount of time that it's in the oven will change.
Robert: And Dale showed me a couple pieces of wood. There was only a 15 degree difference in temperature and one was dark chocolate brown, and the other one was just a light brown.
Bob: Oh, absolutely.
Robert: So just a small amount of temperature variation makes a different color.
Bob: Absolutely. So the lower the temperature, the lighter the color, the higher you go, the darker the color, just like your toast in the toaster.
Robert: But it's not a time thing. You don't leave it in longer to get that? It's just temperature.
Bob: No, you don't leave it. It's just basically temperature. There's three phases in our process. The first phase of the process is a drying phase. So what we do is that Dale's wood will come in and add anywhere between 8% to 10% moisture. We'll take it from that number and we'll bring it to zero. So that's the drying phase, and we probably dry at double the temperature that you would in a conventional kiln. Then what we do is we bring that moisture content into wood to zero. Once it gets to zero, then we start climbing up to the peak temperatures. When we get to the peak temperature, we hold it there for three hours. That's the torrefaction process. It happens there, but you need to have the wood completely dry and at 0% moisture before you start climbing it up. Because if you don't, what ends up happening is that if there's still moisture or any organic property left in the wood, well, this doesn't work like a microwave. It case-hardens the outside as the temperature starts to rise and then it entraps any moisture that's on the inside.
Robert: On the inside. Right.
Bob: And if that happens when outside and inside temperature equate and the moisture can't get out, it expands cracks all the inside of wood.
Robert: Cracks the wood, right.
Bob: Because we've taken wood before and we split it up and we end up with honey coning on the inside and it cracks.
Robert: Oh, interesting.
Bob: You need to make sure it gets to zero. The outside of the board won't give you any information. You'll look at it looks the same as it would any other time, but it's when you split it up to do it. Different species of wood are harder to get the resin pockets out and get that moisture out and would expand the period of time.
Robert: What about the thickness of wood? If you're putting stuff that's really thin in there, do you leave it in longer than something thats already thick?
Bob: No, not really, because what we do is we still sticker it up to two inches. So it's like having the same thing.
Robert: It's the same. Okay.
Bob: But you're right though, in a way, if we only had that in as very thin pieces, let's say you were doing backs on guitars. If you were doing Sitka spruce and just doing the backs and just doing them like that, you'd have to adjust your timing. But we're all set up to do it at two inch inches thick. All we do is we stack. The other thing too is that if you're stickering at every quarter of an inch, let's say, you'd be losing a lot of volume inside the oven to be able to do it, and you'd have to adjust everything.
Tonal effects of torrefaction
Robert: What about tone? What does it do tonally to the wood? We're luthiers, we're building instruments, and a lot of people say, "Oh, the torrefaction process is better tonally." Do you know anything about that? Can you tell us anything about that?
Bob: There is a study that was done in Germany that basically says that, without getting into any scientific stuff because I probably won't remember everything that was there, but that it replaces about 30 years of natural air drying.
So the same process that we did, if you'd have a guitar that was kicking around from the last 30 years and everybody rants and raves about the sound of it, like a Martin guitar or anything like that that's been around, that it has a better tone to it. I've been selling to various luthiers all through North America, and they come back to me and they really tell me that they can pick up their guitars. If there's a bunch of guitars playing, they can pick theirs up because the tone and the volume is a lot higher and the tone's a lot clearer. It doesn't distort up at high pitches.
Robert: So if you were to air dry a piece of wood for 30 years and then put it in, for lack of a better word, the kiln here for 30 for whatever your process is, structurally, the cellular structure, would it be basically the same?
Bob: Basically the same.
Robert: So basically you're speeding up the aging process.
Bob: Yeah. If you take, I don't know if you've been following a lot of the stuff to Martin guitars that they're doing to torrefaction. What they're trying, they're marketing-
Robert: They're pinpointing a year.
Bob: Is they're trying to pinpoint the year, depending on the color and the tonality of the wood. And so a little bit difficult, but it's true in a way. But to be able to say exactly it's one of those years, well, you'd have to have a couple of guitars and be able to compare them, but it does increase the tonality of the wood and people are talking about it all the time, like you said.
Robert: Oh yeah, it's the big news.
Bob: I have no experience and no tools to be able to tell you that. But I'm just taking it from what we're getting from our clients and what they're telling me. We can do any kind of species of wood. So if you wanted to do mahogany or you wanted to do... And again, increase the tonality of the wood because of that, we could do those species. We've done mahogany, we've done spruce, Sitka and Engelmann spruce. We've done the maples, the birch, tamarack or larch. You name it, we've done them all.
Robert: When it comes out the oven here, it's colored. It's brown.
Bob: It's brown.
Robert: How deep does that go? Is it superficial or can I sand through it?
Bob: You can sand through it. Actually-
Robert: You can sand through it?
Bob: Oh, yeah. No, no-
Robert: So you want to be careful. Oh, you can't sand through it?
Bob: I'm incorrect on that.
Robert: Okay. You can't sand through it.
Bob: No matter where you sand to, you're still going to get the same place.
Robert: Okay. Because I would worry about blotchiness depending on how you sand.
Bob: No, you won't get any blotchiness. What you do end up getting though, is that when it does come out of the oven, it looks like crap because all the resins have come to the top.
Robert: Oh, okay.
Bob: And they crystallize there. So you end up with-
Robert: You got to get that off.
Bob: We'll go looking around the shop after, see if we can find something. But you just get this black color on the top. That you need to remove and to sand off. Once you've gone through that, then you're down to this nice rich brown color that you're looking for.
Bending strength
Robert: And it's very brittle wood too afterwards?
Bob: Bending wise and stuff, you lose about 10% of its bending strength. So if you're trying to form around the side of a acoustic guitar, it gets really, really tricky. But what we've been doing for people is that they've actually sent us their piece is already-
Robert: Already bent.
Bob: And then what we do is we make a mold to strap it around, and then we put it in and bring it back out.
Robert: Sure, put it in. There you go.
Bob: Then we use it. But to try to bend them-
Robert: That's tough.
Bob: Becomes difficult because we reintroduce back and after the three hours are done of the torrefaction, we reintroduce 4% to 6% moisture back into the wood at that point. And when we reintroduce it back in, the temperatures are above 150 degrees Celsius at that point. After that, nothing gets back into the wood. We actually have taken these and did some scientific testing where we put this wood into a container that was a 65% relative humidity for a month, measure the moisture content at the end of that month-
Robert: Doesn't take it on?
Bob: Doesn't take it on.
Robert: So it's basically sealed?
Bob: Basically sealed, and very, very stable. So again, it's another interesting point for the music industry because if you're very stable and you're tuning up guitars on a regular basis, depending on where the moisture or relative humidity is in the room or outside or whatever, stable. So you'd have less issues around tuning her up. How many square feet do you have here?
Bob: 46,000 square.
Robert: 46,000 square feet. All of this is eventually going in the oven?
Bob: All this stuff goes in the oven.
Robert: Wow.
Bob: What we do is we've got a manufacturing side over in the corner, and at that point, what we end up doing, we've got molding machines there and we've got planers, we've got saws and everything else. And what we're ended up doing is basically doing all our other products. We don't just do music parts, we do decking, siding and wall components and panels and flooring and a whole bunch of other stuff.
Robert: Very interesting. Wow. Impressive, huh? All right, so tell us a little bit about the standards you were mentioning.
International ThermoWood Association standards
Bob: Well, here, you were talking a while ago about color.
Robert: Yes.
Bob: Okay. And at 185 degrees, you'd have a lighter color of wood. And this was done at 200 degrees because we don't go any higher than that on the softwoods. But we do go for softwoods. For hardwoods, we don't go any higher than 200. For softwoods, we'll go up to 215 degrees. Now where do we get that from? We just didn't pick that out of the air. There's one governing body in the world out of Finland with ThermoWood Association. Finland is where this was created.
Robert: This is all began in Finland.
Bob: Exactly. And that oven actually was developed by Value Tech in Finland. And what what's done is that that ThermoWood Association, they have in turn gone and certified three companies in Finland to manufacture ovens that follow the certification. So they have strict standards to say for hardwoods, if it's an interior application, this is the temperature you go at and the exterior application, this is the temperature you go at. So that's one thing.
The other part too, that's very important to know is that the quality of the product is really operator dependent. You can play around with this. It's all on-
Robert: Oh, sure, you could change it.
Bob: Oh, yeah. You could just go in and everything is computerized. But the recipes, that's where the intellectual property lies. And so my partner, Pierre, he's the creator of the recipes, but he still follows those standards about temperatures and how long we keep it. The rest of it in the duration of the period of time that it's in the oven and how we ramp up the temperatures, those are the intellectual properties. And that's something that everybody should ask questions about. There are operators out there that, for instance, ash, this is maple, but if I take ash for instance, which is a piece that's behind me here, this one here, which we would use for an outdoor application of siding or decking, and this would be a fascia board. This would be in our oven for 80 hours.
Robert: Wow.
Bob: Okay. But there are people out there that do the same thing that will do this in 30 hours. So my analogy is all the time is that you need to ask some questions about torrefaction. It's not, it's torrefied fine. Everybody does the same. Not everybody does the same. And the difference between 30 hours and 80 hours is such-
Robert: That's huge.
Bob: Oh, absolutely. You cook once in a while?
Robert: Sure, sure.
Bob: So I'm sure you've cooked a roast.
Robert: Oh, yeah.
Bob: All right, so if you cook a roast in an hour compared to roast that you cooked in four hours, which one would you rather eat?
Robert: Yeah, the four hour, obviously.
Bob: Exactly. Same thing. It's no different when it comes to this. And it's the same thing. So if you're cooking in half of the time, you're going to cause some stresses into the wood that you wouldn't normally have, or you'll capture some of the moisture inside the wood and get all that cracking that we talked about earlier.
Robert: So it's a slow roast.
Bob: It's a slow roast. And that's the key is to be able to do it as slow as you can, follow it underneath specific standards and have it controlled. All our whole oven is all controlled by PLCs. Once we get it going, it's a non-stop process. It runs all the way through and Pierre's hooked up at it at home. He controls it from there. You can control from anywhere.
Robert: Wow. You don't have to be here?
Bob: Don't have to be here when we do it.
Robert: You could be in Bermuda on the beach running the oven in Canada.
Bob: Exactly. Somebody's just got to load it up and empty it.
Robert: Nice.
Bob: So gives you an idea.
Robert: Sure. Very nice. Yeah. Well, thank you very much for your time.
Bob: You're welcome.
Robert: This is very, very interesting. And if you ever want to work with torrefied wood, give it a shot, folks because it's very promising tonally.
So Francisco in Italy, thank you very much for your question. And remember, like I said, it's not the holy grail of guitar making or instrument making to use torrefied wood. However, it could be one of those small things in your bag of tricks that helps you get a great instrument and happy building.
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