So cold smoking is when you apply smoke to something but you maintain a low temperature in the smoke chamber, typically between 65-85f. You can do it a few ways. You can get little smoking rigs which are metal mesh that goes in a spiral or other pattern that functions as a sort of track for fine wood chips/sawdust. You light one end and it smokes like incense. This goes inside your chamber and generates smoke with very little heat. I use an external smoke generator that's basically a tower with an element at the bottom that you fill from the top with wood chips. This feeds into my smoker through a hole in the side. Personally, I only cold smoke when the outside temperature is lower than 4c. Makes it much easier to keep things food safe, especially when I'm cold smoking chicken.

Cold smoking is most commonly used for foods that have already gone through a curing process such as bacon, smoked salmon, etc. It can also be used for things that would melt at higher temperatures. Cheese, chocolate, and so on. In the case of these sausages, I do a long cold smoke to both get a deep smoke flavour and dry out the sausages casings to get a more snappy bite. I follow up the cold smoke with gradually higher temperatures at the end to fully cook the sausages.