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My DIY, very cheap, very ugly cold smoker!

forktender

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I don't think galvanized would be my first pick to contain food to smoke lol
There isn't anything wrong with galvi as far as food goes until the metal super heats and off gasses. A cold smoker will never get near the heat need for galvi to off gas.
 

bill ace 350

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Wow. I would think you would also have a creosote problem being that your air holes are quite small. I wonder now if I have too much venting. My external smoke box uses a heating element but would you advise me to use my Amazin pellet tray, instead?
I wouldn't feel it my place to advise you to change anything. All i now is that with plenty oh air holes in the bottom, and the ones in the top, i get good good smoke and flow.

I do love the pellet trays though, have 2 of them.
 

bill1

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There may be some confusion over the vapor pressure of metals and what levels are considered "outgassing".

To put Zn in perspective, the RDA is 11mg/day, you shouldn't ingest less than that. A normal diet contains 13mg/day of Zn. The safe upper limit is 40mg per dose (as in per day) although there are plenty of Zn dietary supplements that contain more Zn than that.

Galvanized metals are typically coated with .0008" thick of Zn. A 30 gallon trash can has about 70g of Zn on the inside surface. Heat the trash can to 1665F (907C) and you vaporize that entire 70 grams of Zn. At that moment, we say the vapor pressure of zinc, right above the steel surface (which is still there, just soft) is 1 atmosphere or 101,000 pascals of pressure. A steak with surface area of ~1/4 square foot would absorb ~2% of that total Zn or ~1000mg. That's 25 times the 40mg safe dose limit--that's bad!

But what if you smoke at lower temps than 1665F? If you heat that trash can to 787F (419C), just shy of its melting point, the Zn is then definitely outgassing, but at a vapor pressure of ~100 Pa, 1/1000 of that at boiling, so your hypothetical steak absorbs ~1mg of that Zn. Well, you might argue that in a cooker, maybe all those Zn atoms floating over the entire hot surface might, due to unlucky airflows, all hit your meat. Which means you might eat 1/1000 of the entire 70g, or 70mg, again too much!

But 787F is still an unreasonably hot oven for food. So what about 700F (375C)? Now the Zn vapor pressure is 10Pa, so now we're talking about a max of 7mg on your meal, not really a concern, and that's still an unrealistic cooking or smoking temperature. At 375F (191C, a hot household oven) your Zn vapor pressure is ~30uTorr or 4mPa, and we're talking about micrograms of Zinc "outgassing" to your meat--not a concern. At a normal 250F smoker temp (121C) you're another factor of 100 less. To even plot these curves takes many cycles of logarithmic paper...see e.g.
https://www.oerlikon.com/ecomaXL/files/metco/oerlikon_FLY-0040.2_VaporPressureCurves_EN.pdf


My point is just that, although Zn may be a lousy material to use in ultra-high-vacuum scientific apparatus, it is still a metal and so is far better than the plastics that we associate in practical life with "outgassing". As a metal, its outgas rate at temps well below its melt point is negligible. Outgassing of Zn at 375 celsius is a meaningful concept; at 375 fahrenheit it's "academic" at best.

Now if you put red-hot coals on a galvanized surface you will form ZnO, which readily flakes off, and can follow the draft to your food at potentially harmful milligram levels. Hence galvanized steel is not a metal for fireboxes or surfaces that fire or flame touches. But at controlled oven wall temperatures you're OK.
 

mike243

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Why take chances and condone material that in the wrong hands could hurt somebody? I cant and don't mean to knock anybody , I just think its like playing with poisonous snakes, everything's ok till it aint lol
 

rohfan2112

Smoke Blower
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Joined Oct 27, 2013
Why take chances and condone material that in the wrong hands could hurt somebody? I cant and don't mean to knock anybody , I just think its like playing with poisonous snakes, everything's ok till it aint lol
Again, I'm cold smoking, not cooking. I doubt that temps inside the can would even get as high as 65 degrees, especially in the winter.
 

bill ace 350

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Joined Dec 28, 2013
There may be some confusion over the vapor pressure of metals and what levels are considered "outgassing".

To put Zn in perspective, the RDA is 11mg/day, you shouldn't ingest less than that. A normal diet contains 13mg/day of Zn. The safe upper limit is 40mg per dose (as in per day) although there are plenty of Zn dietary supplements that contain more Zn than that.

Galvanized metals are typically coated with .0008" thick of Zn. A 30 gallon trash can has about 70g of Zn on the inside surface. Heat the trash can to 1665F (907C) and you vaporize that entire 70 grams of Zn. At that moment, we say the vapor pressure of zinc, right above the steel surface (which is still there, just soft) is 1 atmosphere or 101,000 pascals of pressure. A steak with surface area of ~1/4 square foot would absorb ~2% of that total Zn or ~1000mg. That's 25 times the 40mg safe dose limit--that's bad!

But what if you smoke at lower temps than 1665F? If you heat that trash can to 787F (419C), just shy of its melting point, the Zn is then definitely outgassing, but at a vapor pressure of ~100 Pa, 1/1000 of that at boiling, so your hypothetical steak absorbs ~1mg of that Zn. Well, you might argue that in a cooker, maybe all those Zn atoms floating over the entire hot surface might, due to unlucky airflows, all hit your meat. Which means you might eat 1/1000 of the entire 70g, or 70mg, again too much!

But 787F is still an unreasonably hot oven for food. So what about 700F (375C)? Now the Zn vapor pressure is 10Pa, so now we're talking about a max of 7mg on your meal, not really a concern, and that's still an unrealistic cooking or smoking temperature. At 375F (191C, a hot household oven) your Zn vapor pressure is ~30uTorr or 4mPa, and we're talking about micrograms of Zinc "outgassing" to your meat--not a concern. At a normal 250F smoker temp (121C) you're another factor of 100 less. To even plot these curves takes many cycles of logarithmic paper...see e.g.
https://www.oerlikon.com/ecomaXL/files/metco/oerlikon_FLY-0040.2_VaporPressureCurves_EN.pdf


My point is just that, although Zn may be a lousy material to use in ultra-high-vacuum scientific apparatus, it is still a metal and so is far better than the plastics that we associate in practical life with "outgassing". As a metal, its outgas rate at temps well below its melt point is negligible. Outgassing of Zn at 375 celsius is a meaningful concept; at 375 fahrenheit it's "academic" at best.

Now if you put red-hot coals on a galvanized surface you will form ZnO, which readily flakes off, and can follow the draft to your food at potentially harmful milligram levels. Hence galvanized steel is not a metal for fireboxes or surfaces that fire or flame touches. But at controlled oven wall temperatures you're OK.
Thanks! Good to know.
 

bill ace 350

Master of the Pit
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630
Joined Dec 28, 2013
Why take chances and condone material that in the wrong hands could hurt somebody? I cant and don't mean to knock anybody , I just think its like playing with poisonous snakes, everything's ok till it aint lol
I'll keep using mine until i learn that how i use it can be risky.

I use it for cold smoking outdoors .

I uses a pellet smoking tray.

I place the tray on a ceramic tile to keep it from touching the surface of the can.

Doesn't seem to pose a high degree of risk.
 

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