Of clearer consequence on wood properties are those processes involving the heating of the cask. The method of heating may vary, from various degrees of intensity used by European coopers, to an intense charring that is applied by American cooperages for the manufacture of casks destined for the production of bourbon or other grain whiskies. The intensity of heating naturally effects the compounds produced from the degradation of wood macromolecules and has led to increasing interest in more precisely controlling the process. The traditional approach of heating over a fire of oak chips has sometimes been maintained, while more carefully controlling the temperature and duration of heating [34]. Different methods of heating are also being investigated, such as
the use of radio-frequency and infrared energy to heat casks.