Torrefaction experiment

[dshaker]

I've been hearing so much about torrefied wood in guitar magazines that I want to learn more about it. I know (1) it tends to make the wood lighter and stiffer and (2) it is done by exposing wood to heat in the range of 200C to 300C (400F to 575F) in the absence of oxygen. Ordinarily, this process requires piles of expensive equipment, but I want to see what can be done with a kitchen oven and aluminum foil.

So, here is the plan:
Get some spruce brace wood, Sitka probably, and mill myself some slats of uniform length, width, and thickness, probably about 500mm x 50mm x 4mm.
Measure the long-grain freq. for each slat and record. With luck, they should all be close to the same.
Wrap each in aluminum foil, with several folds at each of the seams.
Put them in a 400F oven for varying lengths of time, probably 5 min, 10 min, 15 min, and so on.
Pull them out when done, let cool, take the long-grain freq. again.
Report back.

I don't want to waste a LOT of wood, so that the reason for just doing slats and measuring just the long-grain. For a first approach, that's enough. Then, if it works, I can try a whole soundboard.

Anyone have any suggestions for improvement?

Wordsmith's note: Although the verb is "torrefy", the noun is "torrefaction" which should be pronounced "tor-e-FAK-shun" but it seems like nearly everyone on YouTube acts as if it were spelled "torrefication" and pronounces it "tor-e-fi-KA-shun". Don't let this happen to YOU!

[kiwigeo]

Only one comment from me.....if the process requires absence of oxygen then I don't think wrapping the wood in aluminium foil and bunging it in the oven is going to be a valid test of the process.

40 degrees forecast for Adelaide today and were on a total fire ban........my wood stash is about to get torrified without any oven.

[dshaker]

Only one comment from me.....if the process requires absence of oxygen then I don't think wrapping the wood in aluminium foil and bunging it in the oven is going to be a valid test of the process.

Yeah, it might not work. But I gather the only reason for the absence of oxygen in the process is to keep the wood from burning, outright. I think if I stick to the lower end of the temperature scale and expect longer times, then I'll be in the right ball park. At worst, I waste some spruce bracewood.

[kiwigeo]

Only one comment from me.....if the process requires absence of oxygen then I don't think wrapping the wood in aluminium foil and bunging it in the oven is going to be a valid test of the process.

Yeah, it might not work. But I gather the only reason for the absence of oxygen in the process is to keep the wood from burning, outright. I think if I stick to the lower end of the temperature scale and expect longer times, then I'll be in the right ball park. At worst, I waste some spruce bracewood.

The toughest part of the experiment would be explaining to the fire department why you're cooking up a load of wood in your oven .

[dshaker]

The toughest part of the experiment would be explaining to the fire department why you're cooking up a load of wood in your oven .

I dunno. Tough call between that and the wife.

[aljosha]

please be very careful!
the flash ignition point of spruce is at 350 - 360 degrees Celsius
and the Point for spontaneous ignition is at 390 - 400 degrees celsius
(that's as far as I know)

that might change without oxygene, but no oxygene doesn't mean an oven with the wood wrapped in Aluminiumfoil
no oxygene means no oxygene aka Vacuum
without air a fire cant breath and therefor dies, or in this case does not start
so in my book "torrefication" means drying the wood by burning it in a vacuum

add air to the process and you might end up with "terrification" rather

best
j

[Nick]

no oxygene means no oxygene aka Vacuum
without air a fire cant breath and therefor dies, or in this case does not start
so in my book "torrefication" means drying the wood by burning it in a vacuum

add air to the process and you might end up with "terrification" rather

best
j

Not completely correct there j, the lack of oxygen doesn't equate to a vacuum, a vacuum is any pressure below atmospheric pressure (14.7 PSI), you can still have O2 present in a vacuum, just at a lesser quantity. Remove the 20% of O2 out of air and there's still 78% Nitrogen, and the remaining 2% contains low levels of CO2 and Argon. Torrefaction is carried out at atmospheric pressure so it merely means that in this process the 20% O2 is probably replaced with 20% more Nitrogen but the whole lot is still at 14.7 PSI or above.
Doug, as Martin pointed out, wrapping in foil won't exclude the oxygen so may not give you any meaningful results. Unless you want to flood Mum's oven with N2 You'd probably need to put your Spruce inside an air tight box and flush the air out of that with N2 or Ar then cook the box.

[Nick]

Whoops, double post, hit quote instead of edit!

[Nick]

[dshaker]

Torrefaction is actually used in two different ways. One is to create a fuel that is lighter, easier to transport, and more dense in terms of energy per unit of mass. It really is a modernization of the process of making charcoal. I don't want to do that.

The other is to drive imitate the process that wood naturally goes through over a few decades. In this form, we are just making the wood lighter and stiffer.

I suspect, but don't know, that the latter use can be done at lower temperatures and that, at the lower temperatures, the exclusion of oxygen isn't so important.

But the idea of the wood starting to burn in my stove is a little alarming, though I will say I didn't freak out the last time smoke started to come out of the oven, when it was a chicken I was burning. Still I'm thinking maybe I should be doing this experiment at 350F (175C) instead of 400F (200C).

[aljosha]

hmm...
seems I've found yet another bit of my college education I can scrap...
many thanks for pointing that out nick, I might have to teach myself actual realitybased physics and chemistry at some point...

irregardless of that I realized that were talking of 400 degrees Fahrenheit which is nowhere near 400 deg. Celsius
no clue how I could stuff that up
it's 10PM here but I still might wake up today...
sorry, continue with the experiments

best
josh

[printer2]

Hope you don't mind my late addition. Did my own experiments, started with foil wrapped wood. Eventually got to the point where I baked my wood in the oven at 385 F (195 C). No need for vacuum or protective environment as long as you have good uniformity in the oven. I have a convection oven so the air temp should be fairly even. I start out holding the wood around 240 F (115 C) for a while to drive out the free moisture in the wood. Then I take the oven up to 360 F (182) and let it equalize through the oven and then take it to 385 F (195 C) where the fun begins. Spend about 1 hour at this temperature then turn it off and let it cool down.

I have done some sides before bending but they are more prone to breaking so I am now bending first and baking after. Only got a 26" side into the oven cross ways, found the bottom where the element is got a little more scorched. Baking afterwards reduces this and you can do a dread sized side in no problem. I sticker the wood, don't use a heavy steel bar to weight it down. The gasses that come off the wood can condense on drip down and smoke and catch on fire if it hits the elements. (not going to say how I know) Either way you will have a smoky smell left in the oven when you are done. Oven cleaner will be needed if you have a missus to please.