Hot-smoked chum salmonSmoking is the process of flavoring, browning, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood. Meat, fish, and lapsang souchong tea are often smoked. Smoking is the process of flavoring, browning, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood. Meat, fish, and lapsang souchong tea are often smoked. In Europe, alder is the traditional smoking wood, but oak is more often used now, and beech to a lesser extent. In North America, hickory, mesquite, oak, pecan, alder, maple, and fruit-tree woods, such as apple, cherry, and plum, are commonly used for smoking. Other biomass besides wood can also be employed, sometimes with the addition of flavoring ingredients. Chinese tea-smoking uses a mixture of uncooked rice, sugar, and tea, heated at the base of a wok. Some North American ham and bacon makers smoke their products over burning corncobs. Peat is burned to dry and smoke the barley malt used to make whisky and some beers. In New Zealand, sawdust from the native manuka (tea tree) is commonly used for hot smoking fish. In Iceland, dried sheep dung is used to cold-smoke fish, lamb, mutton and whale. Historically, farms in the Western world included a small building termed the 'smokehouse', where meats could be smoked and stored. This was generally well-separated from other buildings both because of the fire danger and because of the smoke emanations; the smoking of food could possibly introduce polycyclic aromatic hydrocarbons which may lead to an increased risk of some types of cancer; however, this association is still being debated. Smoking can be done in four ways: cold smoking, warm smoking, hot smoking, and through the employment of 'liquid smoke'. However, these methods of imparting smoke only affect the food surface, and are unable to preserve food, thus, smoking is paired with other microbial hurdles, such as chilling and packaging, to extend food shelf-life. The smoking of food likely dates back to the paleolithic era. As caves or simple huts lacked chimneys, these dwellings would probably have become very smoky. It is supposed that early men would hang meat up to dry and out of the way of pests, thus accidentally becoming aware that meat that was stored in smoky areas acquired a different flavor, and was better preserved than meat that simply dried out. This process was later combined with pre-curing the food in salt or salty brine, resulting in a remarkably effective preservation process that was adapted and developed by numerous cultures around the world. Until the modern era, smoking was of a more 'heavy duty' nature as the main goal was to preserve the food. Large quantities of salt were used in the curing process and smoking times were quite long, sometimes involving days of exposure. The advent of modern transportation made it easier to transport food products over long distances and the need for the time and material intensive heavy salting and smoking declined. Smoking became more of a way to flavor than to preserve food. In 1939 a device called the Torry Kiln was invented at the Torry Research Station in Scotland. The kiln allowed for uniform mass-smoking and is considered the prototype for all modern large-scale commercial smokers. Although refinements in technique and advancements in technology have made smoking much easier, the basic steps involved remain essentially the same today as they were hundreds if not thousands of years ago. Cold smoking differs from hot smoking in that the food remains raw, rather than cooked, throughout the smoking process. Smokehouse temperatures for cold smoking are typically done between 20 to 30 °C (68 to 86 °F). In this temperature range, foods take on a smoked flavor, but remain relatively moist. Cold smoking does not cook foods, and as such, meats should be fully cured before cold smoking. Cold smoking can be used as a flavor enhancer for items such as cheese or nuts, along with meats such as chicken breasts, beef, pork chops, salmon, scallops, and steak. The item is often hung in a dry environment first to develop a pellicle, then it can be cold smoked up to several days to ensure it absorbs the smokey flavour. Some cold smoked foods are baked, grilled, steamed, roasted, or sautéed before eating. Cold smoking meats is not something that should be attempted at home, according to the US National Center for Home Food Preservation:'Most food scientists cannot recommend cold-smoking methods because of the inherent risks.' Cold smoking meats should only be attempted by personnel certified in HACCP, or Hazard Analysis and Critical Control Points, to ensure that it is safely prepared.