The Smoking Process - Hardwoods are made up mostly of cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are the basic structural material of the wood and lignin acts as a glue. Some softwoods like Pine and firs hold lots of resin, which produces a harsh-tasting smoke residue. Because of this, these woods are generally not used for smoking.
Cellulose and hemicellulose are aggregate sugar molecules; when burnt, they effectively caramelise, producing carbonyls, which provide most of the colour components and sweet, flowery, and fruity aromas. Lignin, a highly complex arrangement of interlocked phenolic molecules, also produces a number of distinctive aromatic elements when burnt, including smoky, spicy, and pungent compounds like guaiacol, phenol, and syringol, and sweeter scents like the vanilla-scented vanillin and clove-like isoeugenol. Guaiacol is the phenolic compound most responsible for the "smokey" taste, while syringol is the primary contributor to smokey aroma.
A number of wood smoke compounds act as preservatives. Phenol and other phenolic compounds in wood smoke are both antioxidants, which slow rancidification of animal fats, and antimicrobials, which slow bacterial growth.