Short answers, pulled from the story.
Archaeological evidence suggests the smoking of food dates back to the Paleolithic era. Early humans likely used this process to preserve meat and fish for long periods before modern refrigeration existed.
Guaiacol is the phenolic compound most responsible for the smoky taste while syringol is the primary contributor to smoky aroma. Lignin produces distinctive aromatic elements when burnt including smoky spicy and pungent compounds such as guaiacol phenol and syringol.
Smokehouse temperatures for cold smoking are typically between 20 and 30 degrees Celsius whereas the temperature range for hot smoking is usually between 120 and 170 degrees Celsius. Most food scientists cannot recommend cold-smoking methods because of the inherent risks involved in home preparation.
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.
Regularly consuming smoked meats and fish may increase the risk of several types of cancer due to polycyclic aromatic hydrocarbons introduced during the process. Some compounds found in wood smoke including formaldehyde acetic acid and other organic acids give wood smoke a low pH about 2.5 and some of these compounds are toxic to people.