As another writer has stated, there are two types of smoking. Hot-smoking is essentially cooking the fish in the presence of smoke. In that case, the smoke is used as a flavorant, while the heat acts as the main preservation/cooking method. The heat denatures proteins in the fish which make the structure more rigid, and primarily by the same action, denatures proteins in bacterial and fungal cells/spores making it safe to eat. Cold smoking is also used to preserve meats, including fish, and in that instance compounds present in the smoke adhere to the outer surface of the fish. These compounds have antimicrobial and antioxidant properties which lower the surface microbial load on the fish and prevents oxidation of fats which leads to rancidity/spoilage. Cold-smoked meats are often heavily salted and extensively dried during the smoking process. Both of these serve to reduce the water activity in the product. Water activity is a measure of the availability of water for chemical reactions, including those used for microbial metabolism. Therefore, salting and smoking, which reduces the water activity of the product, limit the amount of water which is available to grow spoilage organisms. The food is much more inhospitable to microbial growth and spoilage and is thus able to be stored for longer periods.