Here is a description of how to produce a cheap and effective cold smoker. It keeps smoking for 10-12 hours per filling so if you want to smoke meat or fish for several days, you can do it without interrupting your work or sleep. Just fill it up, fire it and forget it until you wake up or come back from work.
This kind of cold smokers have been described many times. There are even some commercial smokers that you can buy. The idea is to generate air flow with the help of a compressor by having a thin tube within a thicker one. The air flow will keep the wood smoldering and transport the smoke to the smoking house where you put your food (meat, fish, cheese etc.). In this instructable I describe only the smoke generator. For a smoker house, any box made of metal, wood or even cardboard will do since the smoke is cold.
The one described here has enough capacity to keep smoking for 10-12 hours. This is good because if you need to smoke for several days, you do not want to stay awake at night or stay home from work. It keeps on even though the wood may be moist due to the cooking plate underneath. It is desirable to soak the fuel in water for several hours because it generates much more smoke
It is essential that a smoker should be easy to disassemble and clean. It does not take long time before the inside is covered with thick soot. You should be able to wash the whole thing occasionally.
I started with a stainless steel cylinder with inner diameter 140 mm and height of roughly 500 mm. It has thickness of about 2 mm. The cross-section of the chamber does not matter. Any shape will do. If you want it to smoke for a long time, make sure it has enough capacity. Note the screws I mounted on each side of the cylinder. I will use these to tie the whole set-up together after it is finished to avoid toppling and creating a dangerous situation with glowing wood.
Furthermore, I found a steel plate that will be the bottom of the chamber.
The chamber will have 3 x 12mm holes near the bottom to keep the air flow.
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Step 1: The Piping
The chamber will have a top plate to cover the body of the smoker. It is an advantage if this is a bit heavy so it keeps the whole thing together. I used an old electrical cooking plate. It is cast iron so it does the job.
I bore a 22mm hole at the middle of the plate and fitted a short 22 mm copper tube through it. It is important that this joint is air-tight so I screwed the tube to the plate and filled the joint with furnace cement.
I fitted a 22 mm T-joint onto this short tube.
I then assembled a 2-meter long 22-mm copper tube at one side of the T-joint and a 12-mm copper tube at the other side. At the end of the 12-mm tube, there is a nipple to connect to the compressor. The longer teh 22 mm tube is, the better. After all, we are speaking of a cold smoker here.
I stuck the 12 mm tube with the connection to the compressor through one end. In order to make a tight connection between 12 mm tube and the 22 mm T-joint, I wrapped some aluminum foil around the 12 mm tube.
Step 2: Putting It All Together
It is important to keep the wood smoldering even though it may be moist. It is a good idea to use external heat. So the whole set-up is placed on an electric cooking plate. I use a 2000W plate with thermostat. It does not have to be very hot. Just enough to reach a temperature to preheat the wood. I set the knob to less than half power. Some people stick a soldering iron of 15W into the smoker and they claim it works. NB! Get a new iron else, the solder rests may generate dangerous fumes.
Finally, you need the air blower. I am lucky to have an industry size compressor. It is overkill but it works well. It has a pressure reduction valve so I can regulate the airflow as much as I want. You do not need very much air, just enough to generate the necessary circulation. It is said an aquarium compressor will do. I have not tried it so I cannot confirm this.
So, that's all. Good luck with smoking food.