Baking vs Torrefaction

[LFL Steve]

Both of Tim’s assertions
Wood requires oxygen to burn
Nitrogen as an inert gas can exclude oxygen
are correct. Numerous biomass processes, and many many other industrial processes, use exactly the nitrogen purge he describes. Such environments should have oxygen concentration monitoring in the breathing space to guard against asphyxiation of the workers.

[printer2]

Originally Posted by LFL Steve

Both of Tim’s assertions
Wood requires oxygen to burn
Nitrogen as an inert gas can exclude oxygen
are correct. Numerous biomass processes, and many many other industrial processes, use exactly the nitrogen purge he describes. Such environments should have oxygen concentration monitoring in the breathing space to guard against asphyxiation of the workers.

So you are saying my assertions are incorrect then?

[AMW]

Talk about a heated discussion!!!

[soups]

Originally Posted by AMW

Talk about a heated discussion!!!

Some of us should probably come up for oxygen.

[printer2]

Originally Posted by soups

Some of us should probably come up for oxygen.

If you know the world is round but others are saying the world is flat, there are some of us that believe in scientific and engineering principals to back up what they say. So far I have not seen anyone here back up what they say on torrefying guitar wood. I have backed up my stating there does not have to be a protective atmosphere. I have done about a dozen woods, I have read extensively on the process, I worked in the heat processing industry on the equipment used. Even the Taylor video I gave the link to is one of the ovens I have worked on. Originally people were saying the wood is processed under vacuum. I said the heat would not transfer from the elements to the wood with any efficiency, then it changed to pulling a vacuum and a shielding gas used. But no one can show this is actually done.

This is not a heated discussion, I know none here save Tim, if it were not for his post saying an inert gas is used I would not have bothered with the last few posts. But I know he comes from an engineering background and would appreciate knowing if indeed wood can be treated in air. So hopefully he can make heads or tails of my information.

I asked my mentor why he thought I could take over teaching his college courses (he was retiring), he said because I have patience. I never expected that, but he felt it made me a good instructor. So I find it funny this is thought to be heated. (yes I get the heated, oxygen funnies)

"So you are saying my assertions are incorrect then?"

Tim will probably not be back today, maybe tomorrow.

[soups]

Originally Posted by printer2

If you know the world is round but others are saying the world is flat there are some of us that believe in scientific and engineering principals. So far I have not seen anyone here back up what they say on torrefying guitar wood. I have backed up my stating there does not have to be a protective atmosphere. I have done about a dozen woods, I have read extensively on the process, I worked in the heat processing industry on the equipment used. Even the Taylor video I gave the link to is one of the ovens I have worked on. Originally people were saying the wood is processed under vacuum. I said the heat would not transfer from the elements to the wood with any efficiency, then it changed to pulling a vacuum and a shielding gas used. But no one can show this is actually done.

This is not a heated discussion, I know none here save Tim, if it were not for his post saying an inert gas is used I would not have bothered with the last few posts. But I know he comes from an engineering background and would appreciate knowing if indeed wood can be treated in air. So hopefully he can make heads or tails of my information.

I asked my mentor why he thought I could take over teaching his college courses (he was retiring), he said because I have patience. I never expected that, but he felt it made me a good instructor. So I find it funny this is thought to be heated.

"So you are saying my assertions are incorrect then?"

Tim will probably not be back today, maybe tomorrow.

My post was a play on words playing off of AMW’s post. Have a little fun with it

[printer2]

Originally Posted by soups

My post was a play on words playing off of AMW’s post. Have a little fun with it

Yes, my type of humor.

[sinistral]

I think part of the lack of agreement stems from the fact that there is no standard definition of “torrefaction”. In France, “torréfié” is used to describe everything from dried fruit, dry-roasted coffee and dry-roasted nuts.




Here is a blog post from 2023 on Bourgeios’ wbsite:

From Dana’s Bench: How Torrefied Woods Benefit Bourgeois Guitars

At least in Bourgeois’ case (or, more precisely, their supplier, since I’ve heard Dana Bourgois say that they no longer torrefy wood in-house), the process appears to involve a low- or oxygen-free environment:

That ancient practice evolved over centuries, and more uses for heat-treated wood emerged. By the 1960s, the Finns created a torrefaction industrial processing system to roast raw oak floorboards in a temperature-controlled, anaerobic environment to manufacture stable flooring products that resisted shrinkage and warping.

“Torrefaction is the same process as making charcoal; wood is heated beyond its combustion point but denied oxygen,” Dana explains. “Without oxygen, the wood itself can‘t combust. The gases coming off the wood combust. If you heat the wood long enough, it becomes charcoal. The trick for guitar wood is to heat the wood at just the right temperature for the right amount of time. Structural tests have revealed an ideal ‘recipe’ of heat and duration needed for each kind of wood.”

While we wait for Tim to check back in, perhaps Dana Bourgeois’ words will shed some light on at least some people’s processes?

[Tim McKnight]

Some 30 years ago I began experimenting with baking tops in Mary’s conventional cooking oven never exceeding 275*F and it resulted in “baked” tops that I still use today. The process I used was NOT torrefaction. It was merely baking the wood to crystallize and set the resins in the wood. During the process the resins would ooze out of the cells and end grain surfaces. It didn’t darken or stain the wood and the resins sand away easily.


A few years ago I shipped several tops, backs and sides to a company that torrefied some of my wood. It’s the same company that Martin, Taylor, Gibson and Bourgeois used. I am not sure if they are still using that same company or not but they were one of the first companies to torrify tops for the major manufacturers. The owner of that company described his process to me but I don’t remember that conversation well enough to describe it in accurate detail here. I do remember he used a schedule to ramp up and down the heating and cooling cyclical rates and he did say the temperatures were above common wood combustion temperatures so he had to evacuate the oxygen and inject a gas so the wood did not combust. He also mentioned injecting moisture at some point during the process to control stresses. I vaguely remember him mentioning 900*F but I could be mistaken so take that with a grain of salt.

My previous comment about removing oxygen so the wood would not combust comes from him and also from an Ohio state fire academy training I attended which had to do with controlling the “fire triangle”. The fire triangle is a simple model for understanding the necessary ingredients for most fires. The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent. A fire naturally occurs when these three elements are present and combined in the right mixture. A fire can be prevented or extinguished by removing any one of the elements in the fire triangle. Remove any one of the 3 legs of the triangle and combustion can’t take place.

I will defer to Fred’s knowledge and details of the “updated” process which could have changed and evolved since I dealt with it.

[printer2]

Originally Posted by Tim McKnight

Some 30 years ago I began experimenting with baking tops in Mary’s conventional cooking oven never exceeding 275*F and it resulted in “baked” tops that I still use today. The process I used was NOT torrefaction. It was merely baking the wood to crystallize and set the resins in the wood. During the process the resins would ooze out of the cells and end grain surfaces. It didn’t darken or stain the wood and the resins sand away easily.


A few years ago I shipped several tops, backs and sides to a company that torrefied some of my wood. It’s the same company that Martin, Taylor, Gibson and Bourgeois used. I am not sure if they are still using that same company or not but they were one of the first company’s to torrify tops for the major manufacturers. The owner of that company described his process to me but I don’t remember that conversation well enough to describe it in accurate detail here. I do remember he used a schedule to ramp up and down the heating and cooling cyclical rates and he did say the temperatures were above common wood combustion temperatures so he had to evacuate the oxygen and inject a gas so the wood did not combust. He also mentioned injecting moisture at some point during the process to control stresses.

My previous comment about removing oxygen so the wood would not combust comes from an Ohio state fire academy training I attended which had to do with controlling the “fire triangle”. The fire triangle is a simple model for understanding the necessary ingredients for most fires. The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent. A fire naturally occurs when these three elements are present and combined in the right mixture. A fire can be prevented or extinguished by removing any one of the elements in the fire triangle. Remove any one of the 3 legs of the triangle and combustion can’t take place.

I will defer to Fred’s knowledge and details of the “updated” process which could have changed and evolved since I dealt with it.

When I first experimented with the wood I worried about the wood catching on fire so I thought to get rid of the oxygen also. I used a method used in heat treating metals (which is where I gained my knowledge of furnaces and ovens) where you put the part in a stainless steel bag along with a 'getter' that react with oxygen before the part get up to temperature. I made up a bag and put thin wood shavings in to react with the remaining oxygen. The wood did not combust but the shavings turned pretty dark. I then thought, let's try it again but without the shavings. I thought that the moisture in the wood will steam off and blow out any remaining air in the bag. Worked without the wood lighting up. Then for kicks I tried a piece of wood without the bag, the wood did not catch on fire also.

You want to know what did catch on fire? The third run I did with guitar wood which had some pine in with the spruce. The oven I was using was a convection oven, without the fan I do not think I would have the temperature uniformity needed. The elements are shielded behind a sheet of steel and I gave them no thought. Another thing I did not really think of it the steel bar I put on the stack, I have layers of wood stickered and the bar to put some weight on it. Seems obvious now, but the extra sap of the pine evaporated off and naturally condense on the 'cold' steel bar, dripped off onto the floor of the oven. Then the flames came. Learned not to do pine again and not use a weight to hold the stack down. Also use a drip tray since then.

[colins]

For a chemical engineer like me whose day job has involved biomass carbonisation and pyrolysis (yeah, more weird terms) this thread is very interesting. It certainly shows how each industry places its own interpretation on terms such as baking and torrefaction. A couple of comments:

Pulling a vacuum and creating an anaerobic (oxygen-free) environment are quite different.

• The reduced operating pressure commonly referred to as a “vacuum” lowers the boiling points of water and the other volatile components in the material and allows them to evaporate more effectively at lower temperatures, potentially allowing useful evaporation while avoiding chemical changes that may occur at the higher temperatures needed if a partial vacuum is not applied.
  
• Working in an anaerobic environment (typically achieved by displacing air with nitrogen) does not involve reduced pressure. It is useful to process materials above their ignition temperatures. Certainly it is the case in industrial biomass pyrolysis, which tends to take the wood up to between 400 and 500 deg C. Wood is a variable material and its ignition temperature varies also, with one article suggesting its ignition temperature ranges from less than 190 deg C through to almost 500 deg C depending on the wood.

The rate of temperature change and period at high temperature can be very important. For the industrial wood pyrolysis I deal with (heating in an anaerobic environment to 400-500 deg C), most people seek one of two main outcomes. Slow pyrolysis, over say 30 minutes, decomposes the wood to predominately charcoal and gas, with just a little liquid. In contrast, fast pyrolysis in a fraction of a second can convert 70% or more of the dry biomass to liquid, with only small amounts of char and gas produced.

Back to Soups’ original post. Tim’s comments about the temperatures he used for baking coupled with Fred’s excellent charts show that baking may get into temperatures where chemical and physical changes may take place in the wood, just as they can during torrefaction. This, and my own experience, show that the devil is in the detail, with rate of temperature change, highest temperature reached, period at elevated temperature, wood thickness and oven loading all potentially contributing to the outcome. I suspect that is why many guitar makers that use torrefied wood tops prefer to purchase them from specialist suppliers rather than make them in-house.

Colin

[Tim McKnight]

Thanks for also contributing your experience Colin.

I do remember a conversation with the man whom torrefied my wood stating that the torrefaction process was developed to "water proof" wood used in the outdoor project industry such as for decks and fencing. I thought it interesting that our (guitar) industry had adopted an adaptation of that process to use in guitar making.

Another benefit to [us] that is worth mentioning, using torrefied and or baked wood, is a resistance to moisture exchange with surrounding elements. That benefits the player in a more reliable, longer lasting set up and consistent tone from their instrument.

[printer2]

Originally Posted by colins

For a chemical engineer like me whose day job has involved biomass carbonisation and pyrolysis (yeah, more weird terms) this thread is very interesting. It certainly shows how each industry places its own interpretation on terms such as baking and torrefaction. A couple of comments:

Pulling a vacuum and creating an anaerobic (oxygen-free) environment are quite different.

• The reduced operating pressure commonly referred to as a “vacuum” lowers the boiling points of water and the other volatile components in the material and allows them to evaporate more effectively at lower temperatures, potentially allowing useful evaporation while avoiding chemical changes that may occur at the higher temperatures needed if a partial vacuum is not applied.
  
• Working in an anaerobic environment (typically achieved by displacing air with nitrogen) does not involve reduced pressure. It is useful to process materials above their ignition temperatures. Certainly it is the case in industrial biomass pyrolysis, which tends to take the wood up to between 400 and 500 deg C. Wood is a variable material and its ignition temperature varies also, with one article suggesting its ignition temperature ranges from less than 190 deg C through to almost 500 deg C depending on the wood.

The rate of temperature change and period at high temperature can be very important. For the industrial wood pyrolysis I deal with (heating in an anaerobic environment to 400-500 deg C), most people seek one of two main outcomes. Slow pyrolysis, over say 30 minutes, decomposes the wood to predominately charcoal and gas, with just a little liquid. In contrast, fast pyrolysis in a fraction of a second can convert 70% or more of the dry biomass to liquid, with only small amounts of char and gas produced.

Back to Soups’ original post. Tim’s comments about the temperatures he used for baking coupled with Fred’s excellent charts show that baking may get into temperatures where chemical and physical changes may take place in the wood, just as they can during torrefaction. This, and my own experience, show that the devil is in the detail, with rate of temperature change, highest temperature reached, period at elevated temperature, wood thickness and oven loading all potentially contributing to the outcome. I suspect that is why many guitar makers that use torrefied wood tops prefer to purchase them from specialist suppliers rather than make them in-house.

Colin

I was looking for a particular paper as it had a really good graph showing the decomposition to temperature, maybe I will try again yet. Assimilating the information I had on torrefying wood I learned the chemical side of wood bending. This was back in my early days of building and I was still working on my method, with all the different temperatures people use, mist with water or not, kind of confusing. The use of water lowers the temperature needed to bend with, I seem to recall the amount of water vapor changes curves when torrefying wood. I do like the look of baked wood, not too enamored by torrefied wood though.

I was more interested in the stability it can give to humidity changes. I started to do an experiment, I had three sets cut next to each other and I heated them all just above boiling to drive out all the moisture. I then heated two sets to below where torrefaction takes place to any great amount, then torrefied the one. Humidified them and then set the torrefied one aside. Then I repeated the heating of the other two to their respective temperatures. Rince and repeat a number of times. Then I wanted to test the wood and then make a mule that I could swap out the tops to see how they faired. Sadly everything got interrupted before I could learn anything (oh yeah, used to work in a mechanical test lab) and the plates got mixed up with my other wood. I did have another set that were not cut along side the others, did the same to it as the middle one above but after baking I stuck it in the freezer for a few days and then humidified it then back in the oven. I wanted to see if I could 'season' wood driving moisture in and out many times and see if I can make it an 'old' piece of wood without waiting for years. I will have to try it again some day.

[soups]

This has been an extremely interesting thread. Thanks to all who have given input.

[ytse43]

I'm going the (simplified--please don't ROAST me!) linguistic route here. 'Torrefy', also 'torrify', comes from Latin, hence its usage in French. 'Bake' and 'roast' both have Germanic roots.
So, might the word one uses depend on where one grew up?
Regarding this heating process as it pertains to musical instruments, 'torrefaction','torrefying', 'baking', and 'roasting' do get used interchangeably by many of us, as being pedantic is not something most people pursue.

Now, as to this/these process/es being distinct enough to warrant specific use of those words is what other posts here have already gone into.

I have it in my mind that YAMAHA was the first to go mainstream with their A.R.E. (Acoustic Resonance Enhancement ) 'wood reforming' process. https://www.yamaha.com/en/tech-desig...hnologies/are/

Interesting, the words 'torrefy' 'roast' 'bake' 'heat' 'cook' 'fire' 'pyro' are not used in the article, only 'wood reforming'.

Side note: Japanese charcoal briquettes are considered by many to be the best. Japan connection coincidence?

Grammar note: I went with single quotes, despite me being American. Easier on the eyes, and I'm also freed up to put commas outside!