Cold-smoking, along with hot-smoking, is one of two ways to heat fish in the smoking process. It can be prepared in a wet cure that involves marinating in brine, or a dry cure with salt. The fish is smoked at 70 to 90 degrees Fahrenheit and has a shorter shelf-life than hot-smoking. (see Reference 1)
First, you'll need the right materials. Many smokers on the market will get too hot (and are non-adjustable) for cold-smoking. It is possible to build a cold smoker at home. Online resources will tell you how. If you're buying a smoker, one recommended for cold-smoking is the Bradley Smoker, which is specially designed for hot- and cold-smoking. The temperature has an adjustable setting and it's possible to turn off the internal heat. One method to adjust heat in a smoker is adding ice to the heat chamber (see Reference 2).
Salmon is most often used for smoking, and it helps to research varieties of salmon to see which has the desired level of flavor. You'll also need ingredients for the brine if you're wet-curing. This includes pickling salt or kosher salt, sugar, maple syrup, garlic, peppercorns, and water.
Fresh salmon should be scaled, boned, and frozen before it is brined. If your salmon has bones, you use needle-nose pliers to remove them. Cut pieces into 1 1/2-inch to 2-inch pieces if the whole fillet will not fit in the smoker. Leave the skin on, you'll need it to keep the meat together during the smoking process. The salmon must be frozen for best results. Freeze fresh fish, if you can.
Brining and Curing
Choose a brine recipe. Thicker fish will need more brine and must be smoked longer than thinner fish. Boil all ingredients in a pan, simmer for five minutes, cover and cool. Refrigerate until the brine is 40 degrees Fahrenheit or less; it must be between 35 and 40 degrees when adding the fish. The salmon must be marinated for 6 to 12 hours. Rinse salmon under running water for half of an hour to get rid of excess salt. Try a piece of the fish to see if it is still too salty, and if so rinse longer. Let the salmon rest in the fridge for 12 hours to cure. A coating on the fish will appear from protein reactions; it is called pellicle and is necessary for the smoking process.
Follow instructions for cold-smoking on the Bradley smoker or make sure that your homemade smoker allows for cold-smoking -- the smoke doesn't get hotter than 70 to 90 degrees Fahrenheit. Place the fish in the smoker and let it smoke for 12 to 16 hours. Vacuum-sealing your fish after it is smoked is the best way to store it. You can freeze and then thaw as you like, enjoying it year-round.