Torrefication (Torrefaction)

How C.F. Martin and other guitar makers are using the age-old technique of torrefaction to artificially age guitar tops.

The torrefaction of wood is an ancient process that was further developed by Viking societies in what is now Scandinavia and Northern England. Typically, wood or grain stores are exposed to extreme heat in a low-oxygen setting to avoid combustion, so as to remove moisture. Not only does this process remove moisture absorbed from the outside world, it removes moisture inherent within the cell structure, permanently altering the material in cellular interiors.

Its original purpose was to increase resistance to the effects of variable humidity in the environment, greatly reducing decay in animal feed, while torrefied wood used in outdoor construction repels precipitation and resists swelling and cracking. Today, it is used on an industrial level to create wooden fuel pellets that produce heat energy in a cleaner, highly efficient manner.

Only recently was it discovered that torrefaction alters the cellular structure of the treated wood, so that it is almost identical to wood decades or even centuries old, when viewed under a microscope.

*This article was revised in November 2016*

Toasty and Tasty

The slang term of a “toasted top” is being used these days to describe torrefied spruce, because it often has patches or streaks of brown tints, not unlike a piece of toasted bread. But other than darkening the whitish spruce to a greater extent based on how long it is torrefied, the popular name is inaccurate.

Where toasting requires ventilation and constant airflow, torrefication requires the opposite to keep the wood from bursting into flame and ultimately incinerating at the ridiculously-high temperatures required to “artificially age” the wood.

C.F. Martin & Co. has quietly been looking into torrefied wood for some years now, after studying torrefication techniques in Finland, where it has been used since the Middle Ages to treat building timber. The process is 100% chemical free, which fits well into the company’s commitment to responsible environmental practices and concerns.

Finnish guitar makers like Juha Ruokangas have been experimenting with torrefaction since the mid-1990s and compiling the scientific data as to why and how it affects guitar tone.

In a press release dated January 12, 2015, Martin announced their new Vintage Tone System, or VTS. This is a proprietary form of torrefaction that micromanages the process, allowing them to zero in on an artificial age. It also allows for torrefied tops without the telltale toasty streaks. Read more about Martin’s VTS HERE.

Luthier Dana Bourgeois has been experimenting with torrefication in a more visible way longer than other American builders, as was Huss & Dalton. Gibson has been using torrefied fingerboards for some time, and Bob Taylor believes strongly that a torrefied top will guarantee fewer structural issues as a guitar ages. And given the recent high-profile success of the new Martins with torrefied tops, I expect to see it springing up in many more places sooner than later.

Colorful Results

At first, Martin expected to use torrefication as a way to introduce a change of color into the wood, for things like fingerboards or top shading without the use of toner or dyes, so long as there was zero negative impact upon tone production. Instead, they stumbled upon a change in tone that was very much for the better.

According to Tim Teel, Martin’s Director of Instrument Design, they made an R&D test guitar, basically an HD-28 with a spruce top that had been shaded via torrefication. For Teel, the results were startling.

“I immediately noticed it had this chime to the trebles that I recognized from some of the old Martins we have from the 1920s and 30s.” he said to me, as he took out examples of spruce that was torrefied to varying degrees.

There is an old method of dating wood called the Candle Test, used to date violins. Holding a light behind wood recently harvested will show a bright round spot of glowing orangeish-yellow. Older wood, of say 100 years in age, allows much less light to show through, while wood that is 200 or 300 years old will show little or no light at all.

Why this happens remains a mystery. But it makes sense to me that the matter inside the cells or between the cell walls (cellulose and sugars, etc.) has become crystallized to the point that it refracts the light, or otherwise somehow absorbs it.

The spruce used on the first VTS Martins register on the Candle Test to be about 300 years old.

Since 2015 Martin has offered two levels of torrefication. M2 is the designation similar to their first torrefied tops, but is not being mentioned in public with any particular age associated to it.

The M1 designation has little or no noticeable color change and is being touted as targeted to approximate spruce used during Martin’s Golden Era of the early twentieth century. The tops appear slightly yellowed or off-white, compared to spruce that has had no cosmetic toner applied. This spruce is toner-free, yet it still resembles the sound board on a vintage Martin.

Originally reserved only for the Authentic Series of vintage reproduction models, M1 VTS torrefication has since appeared on several limited editions and is now available as a Custom Shop order. Check with your Martin dealer to find out which spruce species are included for custom Martins and with VTS tops.

The marketing language implies they are able to zero in on a specific decade. I recall the behind the scenes language used at the Martin factory was “80 to 100 years old” when it came to using microscope comparisons between the M1 torrefied spruce and spruce taken from actual vintage Martins.

Increased Stability and Accelerated  Tone

Torrefied tops do not react to changes in relative humidity like those made with normal spruce. The spruce is less likely to swell or sink due to the time of year or how dry or wet it is outdoors. According to one Custom Shop employee the torrefied tops do not react to humidity at all.

A senior member of the Repairs department told me that the first Martin made with an experimental torrefied top was donated to a non-profit organization to auction it off. The guitar was left in a glass case under bright lights, where it dried out and cracked. The torrefied spruce allowed for a tiny crack under conditions that would have split a typical new top from bridge to end block.

But it is the way the torrefied spruce sounds that has everyone at Martin so enthusiastic.

Does it sound just like an old guitar? Well, in my opinion, I will say it sounds noticeably different and for the better compared to similar guitars made with normal tops. It makes a brand new guitar sound more alive and awake and responsive. It increases the “openness” and may also increase the high treble ring, so that a top made from Sitka spruce or European spruce acquires a chime more Adirondack spruce.

To my ear, Sitka spruce tops benefit most noticeably from the VTS treatment. But guitars made with Adirondack tops do indeed sound more opened up, with played notes encountering less resistance from the soundboard, so the tone swells effortlessly in all directions, rather than skipping along the surface of the voice like a stone across a lake – my typical metaphor when describing the sound from a brand new Adirondack spruce top.

Most of the new Martin models released for 2015 have torrefied tops, and the entire Authentic Series have been upgraded to M1 torrefied tops, braces and bridge plates.

The Future

Torrefication processes at Martin are now well established. From the get go I met no one who works there that wasn’t noticeably excited whenever it was mentioned. So I think it is safe to say you ain’t seen nothin’ yet compared to what we will be seeing down the line.

We shall also be seeing more and more torrefied wood from other guitar manufacturers. Wood charmer Dana Bourgeois has only become more enthralled with the results and potential of torrefication, and Winter NAMM 2015 revealed that Taylor’s 600 Series is now converted to torrefied Sitka spruce with maple back and sides. The damn has burst, so hang on to your hats!

And that is one man’s word on…

Torrefication of wood used for acoustic guitars

More Reading:

Martin’s New Vintage Tone System

Juha Ruokangas Video Lecture: “Thermo Treated Tonewood – Vintage Vibe or Voodoo?

Dana Bourgeois Recent Commentary in Acoustic Guitar Magazine

Martin OM-28 Authentic 1931 Review

16 thoughts on “Torrefication (Torrefaction)

  1. I don’t really trust torrefied wood. I can’t help but think it will cut down on the wood’s longevity. And or make it brittle or brittle sounding. And the word vintage is overused these days. I don’t care that much about how wood looks. I care more about sound and longevity.

    1. Well what do you mean by longevity, Jane?

      I think most people who are buying the modern guitars that are made lighter, with thinner woods and thinner braces, and thinner finishes, and having no truss rod, or having torrefied wood, care about now, and want the guitar to sound good now, not years down the road. And do do not care at all how long the guitar is going to last after their own lifetime is done and over with.

      That being said, it has been a quarter of a century since guitars were first made with torrefied wood, and I have seen no reports of those guitar having longevity issues. It appears to be the opposite. One of the first Martins made with a torrefied top was left to dry out under hot showcase lamps and the resulting crack was actually truncated because the wood was torrefied, rather than splitting from bridge plate to end block as might have happened with a non-torrefied top. While that is only one guitar, the science behind torrefaction suggests it makes wood more stable, not the opposite, because it no longer reacts to relative humidity in the same way, if at all.

      I will probably never own a torrefied guitar. I like the breaking in process and knowing my playing is forever influencing what that guitar will become after I am gone. I also think Sitka benefits more tonally from torrefaction than Adirondack, but there is no doubt that any spruce treated with Martin’s VTS takes on greater depth and resonance right out of the shipping box.

      And while I know some people who like the look of their VTS top, I know nobody who is buying such a guitar because of how the top looks, they are buying because of how it sounds.

  2. I wonder how old is the oldest known torrified guitar? I’m very interested in getting a sense for how the sound changes over time, compared to a nontorrified guitar like my HD-28. BTW, your articles are really well written and unusually informative. I greatly appreciate the time and effort you put into this labor of love!

    1. Well thank you, Mark.

      That is a very good question. The answer was almost certainly built in Scandinavia. But I will look into the matter, at least insofar as American luthiery goes.

      A good friend of mine owns the Martin guitar that was used in the Sonic Sitka project. That was where various respected guitarmakers made one guitar with a top that had been treated with an early version of torrefaction.

      In this case it is basically an HD-28 with some special cosmetic appointments, and it is a very nice guitar. It has not been played much, as it was in Martin’s possession until it became a raffle prize at a summer drawing at this year’s Martin on Main festival.

      I do not remember who else took part in the project or how far back torrefied tops go in America. I will update this post once I find out more information.

  3. Sperry,
    One of the main rules in an acoustic jam: don’t step on the mandolin….;-) Another big rule for any jam: If you are not soloing, lay the “f” back in the mix. Slightly muting with the heel of your picking hand can help with laying back.
    There are so many players in this world who would give up one of their most precious body parts to have a guitar as responsive as what you are describing. As you previously stated, this guitar could help you improve your picking technique. That would be your better approach for this guitar, imho.
    If you are impatient, you could always attach some ‘duct’ tape to the underside of the guitar’s top. Start with one piece of tape and add more until you achieve the desired level of dullness. Tie-dye or psychedelic duct tape works best…;-)

    warm, non-brash, greetings from 90232,

    1. That is pretty funny, Rusty, thanks.

      Of course, not everyone wants to have to manipulate a guitar, when there might be other guitars out there that simply fit their tastes as is. That being said, there are things about every guitar I ever owned that I wish were at least a little different, but other things that so make it worth having.

  4. Excellent recap.

    I have a custom D-18 VTS Adi that is certainly a unique animal. I have yet to put my hands on anything quite like this. After two moths, I am still trying to determine if this is the guitar for me.

    The sound is rather… brash, and requires a concerted, subtle touch. It jumps out there with the least provocation. And, in my beginner-mediate hands the sounds I produce never seem to stand up to my friends’ with many more years of experience and subtle touch. I hear things when other more experienced players coax out the subtleties I can’t seem to find on a regular basis. Yet their enthusiastic attacks seem to just grow and growl as one might expect a roused beast to when poked / picked.

    One of my concerns is whether the VTS will actually ‘open up’ beyond what it’s laboratory cellular modified status might offer out of the box. Should I expect things to ‘settle down’ a bit from its current loud bark? Or, should I learn to handle him with deftness that requires control easily foregone after no more than 2 glasses of Pinot? Is what I’ve got what I get?

    Also, with the top / braces the only components receiving VTS treatment, will the back and sides need time to catch up and meld with the ‘authentic’ tonal qualities of the glorified VTS treated wood? I suppose I and we will have to wait a few more years to get an ‘authentic’ answer to this query.

    Thanks for the splendid reviews.

    1. Thank you for the complements!

      As to the question of breaking in, the answer is actually no, it will not break in, at least when referring to the traditional version of the term. According to those familiar with torrefied wood, this has already happened due to the VTS, at least when it comes to the inherent moisture leaving the wood and the cellular structure crystallizing so that it refracts light, and possibly sound waves, as they pass through the wood.

      But you have only begun the process of vibrating the heck out that torrefied top, and I know of no one who claims to be an expert on what will actually happen to it in terms of tone production over time. It may be dried out, and may be reacting like a 200 year old piece of spruce, but all that playing and vibrating all those dried out cells must do something to them over time.

      Likewise all the glued joinery, the mahogany back and sides, the spruce bracing and bridge plate will all certainly go through a breaking-in and opening up process – but in the case of the Authentic series, they have their braces and plate torrefied too.

      One would have to play your D-18 along side other VTS examples to determine if you have an unusual or a typical example. But it is no doubt the VTS will make it sound different than a non-VTS D-18.

      I haven’t yet seen any mahogany guitars with torrefied tops of any spruce. And your report has me even more intrigued.

      “Brash,” “jumps out” with a “loud bark” and “requires a concerted, subtle touch.” It almost sounds like you are a person who is used to Sitka spruce on mahogany Martins encountering Adirondack spruce for the first time.

      And to some ears, torrefied Sitka does sound more like Adirondack spruce than typical Sitka – including Tim Teel at Martin, and that is what led them to experimenting with what they now call their VTS treatment.

      Drier and with accentuated peaks in the highest timbres is what I tend to hear from the VTS, along with a more 3D presence in the middle of the voice that is most noticeable when played alongside non-VTS guitars. That is part of being “opened up.” The tone doesn’t just come out as a wall of sound on the surface of an expanding “tone bubble.” There is more going on inside the bubble, which gives it depth and character not heard in new guitars without torrefied spruce.

      To date, I have had one opportunity to play two of the same model with and without VTS, side by side. and they were examples of the D-28 Authentic 1941 currently for sale at Maury’s Music, in Coaldale, PA.

      But that same depth phenomenon shows up in general when it comes to torrefied spruce tops. But the accentuated high-end stuff, which may be what you are calling “brash” may in fact not be for everyone. And that is why I remain surprised that Martin does not offer non-VTS versions of the Authentic models.

      Since mahogany is already bright and forthright, I can see why VTS might over-do such things for some ears. But as I said, I have yet to hear that combination of mahogany and VTS on the same guitar. But I hope to soon.

      1. Thanks for responding to my inquiry.

        Agreed. Since the only wood that is torrefied is the top, I have to assume that between the braces, glue, back/sides, etc. things will start to move around and at some point and settle in. As for the VTS top, I agree with you again in that all those vibrations are bound to cause a stir of some sort. It’ll be fun to experience it first-hand.

        You are correct. I am a (aged) Sitka guy and wasn’t quite ready for what the new VTS Adi voice offered. It’s like walking into a room wearing nothing but your underwear. There is no subtle way to blend in.

        Same with playing this beast in a jam. It just barks and growls, and barks some more. Recently, a mando player had to scoot his chair out of the way a bit so he could hear himself play. Of course, my beginner-ish banging and clanging might have something to do with it too. Offering a svelte touch does wonders for the output in my opinion.

        I switched to 12ga (EJ16) stings a few weeks back and this definitely took some of the rare, endangered warmth away. I planned to play them out to see if I like the lighter gauge in regards to helping me properly fret the B and high E strings. I frequently get buzz on the first and second positions if I’m not diligent – when playing mediums. I know this is partly a result of improper form. However, overall I felt the medium (EJ17) strings were a bit laborious at times.

        Now that the light strings are about dead the sound seems to have mellowed into itself a bit. There is even a hint of that rare and endangered, inviting warmth that presents it’s subtle glow occasionally.

        I’ll switch back to mediums and see how that goes after a few weeks of playing the lights. This may or may not have an effect on my perception of the sound. But I’m interested in experiencing the difference. I’ll also ask some of my jam buddies if they hear anything different… I have been bugging them about their opinion of the sound of my guitar incessantly. So, I’m hoping they have developed an ear for it’s tonal characteristics.

        I have to wonder what a VTS Adi top on rosewood (D28 ’37/’41A) would sound like. Specifically, something with forward shifted bracing. Would the RW help tamp the Adi bark somewhat? Or, is Adi just loud and proud no matter what back/sides it sits atop? I have heard your reviews of these guitars and read them too. All excellent information, BTW. But it is so hard to truly hear and feel what the woods present unless it is in your hands being played.

        And so it goes. Loving the one you’re with…

  5. Hi from Australia, I believe that Maton has been using a similar process for its top woods for decades, resulting in guitars that are extremely stable and reliable, as well as nice and open from day #1. Not everyone likes the ‘Maton sound’ but all Matons seem to have this open character which I attribute largely to the kiln treatment of the top woods.

  6. Hi Spoon.

    Do you know how Martin’s torrefication process (or Dana Bourgeois and other’s) compare to Yamaha’s A.R.E. process?


    1. Hi Jim,

      They are basically the same thing,looking to achieve the same goal of effecting changes to wood that greatly resemble the effects of natural aging – crystallization of the cellular interiors, and breaking down fibrous cellulose, etc. But I do not know how they differ in terms of the details.

  7. Thanks for the informative round-up of this process.

    In addition to Bourgeois, I know that Huss & Dalton is already selling guitars with their “Thermo-Cured” tops and I’ve seen reports from one dealer that Collings is experimenting with torrefied tops (not sure if anything is for sale yet). Clearly something big and exciting is going on.

    I wonder how customizable this process is. I wonder if one can control torrefaction to the point where there is a unique Martin torrefaction sound, a special H&D Thermo-Cure vibe, and a distinctive Bourgeois Aged Tone tone. And, of course, we know that certain builders have a talent for working with certain woods – I wonder if a new torrefaction guru will emerge (or perhaps Dana B. is already there).

    I also wonder if torrefied Sitka retain its Sitka-ness vs. torrefied Adirondack – or if the process makes these unique wood tones sound more similar. Have you had a chance to hear different torrefied woods?

    Finally, I’ve no doubt that adding another process, and one which improves tone – will add a hefty up-charge – but I wonder what this might mean for the prices of non-TF’ed guitars.

    It’s a brave new world, I suppose we’ll have to wait and see on a lot of this.

    Thanks again!

    1. It is my understanding that the modern technology, assisted by the microscope, is getting better and better at zeroing on a time machine that can dial in how far back in time they wish to go, in terms of replicating old wood. Of course replicating is not at all what they are really doing, but that is what they are shooting for. But I believe the notched on said dial are pretty far apart, like maybe 90-year increments and event hen Mr. Peabody and Sherman may land a good ten years before or after their target date.

      It is all still very much in the experimental phase where guitar soundboards are concerned.

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