Sunday, December 02, 2007

From the Kai Lab: Cold Smoker

Nothing beats the sweet, smoky odour of food prepared on a smoker. While many New Zealanders own small smokers which hot smoke food, backyard cold smoking isn't nearly as widespread an activity. This is a shame as cold smoking allows greater control over the flavour of food being smoked. It can be time consuming but as is often the case, the end result makes it well worth while.

Cold smoking is the process of using smoke to cure and flavour foods without cooking them. In the past, this was done as a means of preserving fish and game for consumption during the leaner, less bountiful times of the year. The temperature range is between 12 to 25 degrees celsius, or room temperature, and the smoking time can take anywhere from a few hours to several days. To eliminate the risk of spoilage, the food can be cured, in the form of salting or brining, prior to smoking. Large setups allow for the smoking of chicken and game birds, fish and large cuts of meat. Cold smoking is ideal too, for flavouring small produce such as cheese, olives and salt.

To achieve the necessary low temperatures, the fire needs to be kept separate from the food being smoked. This is achieved by drawing the smoke from the heat source to the smoking chamber through piping or tubing, as seen in the technical diagram below.

With ideas cribbed from various books and websites, and with the help and expertise of Chocky, friend and backyard engineer, I set out to make my own mini cold smoker. Basically, it comprises two large stockpots; one sitting on an electric hotplate, connected to the other pot by a length of duct pipe. With the hotplate on, smoke from the smouldering sawdust is drawn into the other pot through a little battery-powered computer fan, with the heat dissipating as it makes its way across the divide - simple as that!
I was going to need:

  • 2 x 9 litre stockpots (mine were cheapies from the big red shed, a tenner apiece)
  • Duct pipe, 3 metres long, 100mm circumference (found at any hardware store; mine cost $25)
  • Computer fan (whipped from an old computer case; 12 volt)
  • Empty can, 100mm circumference (or as close as you can); also, it needs to be large enough to hold the fan (the fan was a tad bigger than the can, but you'll see what I did to get around that)
  • Electric hotplate
  • Grinder, jigsaw, drill, rasp and other assorted tools
  • 12 volt battery (a car battery)
  • Cable ties (pipe clips would be good but I couldn't find any for the duct pipe in a 100mm size)
  • Wire, to extend those already on the fan, about 1 metre in length
  • Clips, for the wire so it can connect to the battery
  • 2 wooden drawer handles
On to business: I drew an outline of the can on the bottom of one of the stockpots with a marker. I drilled a little hole for the jigsaw and began to cut my circle. When you're finished, use a rasp to file off any jagged edges and then wash the pot to remove filings and dust. This pot is our smoking chamber.

The empty can will stick out of the hole in the bottom of the pot - this is what the duct pipe will be attached to.

Chocky built a stand to hold the smoking chamber, using scraps lying around the workshop. We have a tripod, about a metre high with a supporting platform. The hole is to accomodate the can poking out of the smoking chamber.

Slits are cut in the top of the empty can and then flared to stop it from slipping through the hole in the bottom of the smoking chamber. It's hard to make out in the photo but the can holds the computer fan. It initially wouldn't fit, so I ground down the corners with my grinder. Don't take too much off; you want it to be absolutely snug inside the can. The fan will draw the smoke up through the duct pipe from the pot on the hotplate.

Place the smoking chamber over the hole in the platform. Pop the can into the hole in the smoking chamber, which in turn should be sitting over the hole in the platform. I was going to rivet the can to the pot, but I wanted to make the unit portable and easy to disassemble.

The fan's wires come out of the top of the can and lead out through a hole I drilled through the bottom of the pot.

With the smoking chamber sitting on the platform, add your extra length of wire and then the clips for the battery.

Take one end of the duct pipe and attach to the can with your cable tie or clip.

Now for the other pot - this will hold the sawdust and sits on the hotplate.
Cut a hole in the pot lid for the other end of the duct pipe. Make it slightly smaller than the diameter of the pipe - it will make for a snug and secure fit. File any rough edges, rinse the lid in water to get rid of dust and filings, then slowly twist the pipe into the hole. Now screw the two wooden drawer handles into the lid; wood is a poor conductor of heat, so no burnt fingers for you when it comes to removing the lid to add more sawdust.

As mentioned before, the smoke in this pot is generated by the smouldering sawdust, heated by the hotplate. As the heat rises, it carries the smoke up through the pipe. With three metres of pipe to traverse, the heat quickly dissipates so by the time it reaches the smoking chamber, the smoke is at room temperature.

Voila! One gleaming cold smoker, ready for action.

All I need now is to install some circular racks inside the smoking chamber to hold the food - a visit to some second hand stores and a garage sale or two should turn something up - old barbecue racks or similar should do the trick. Once that's done, it'll be time to give it a whirl - I'm thinking about re-visiting my previous bacon experiment and later, I'll smoke some peppers to make my own smoked paprika. I'll keep you posted...

A big, sabre-rattling "huzzah!" to Chocky for all his help (he practically built it all) - cheers, son!


Anonymous said...

Hi Nigel,

Used you instructions to make some bacon and for a first try its not toooooo bad. Will adjust the salt and add more honey with a dash of saltpetre to give it a nice pink colour.
Also thanks for your great idea for the cold smoker.


Nigel Olsen said...

Hi Richard,
Good to hear you've given it a go! The beauty of using manuka honey is that it's quite strongly flavoured, hence the relatively small amount I used. It'll be interesting to see the colour after it's been cold smoked.

Donna Barr said...

Hi tech and flash! I'm going to try to do the simplest cold-smoker on earth. If it works, I'll be back (listen for the swearing as the experiments go wrong...)