Hi Jon, heating helps to shape the staves, the more heat the easier to bend but also heat brings the sugars and flavors in the wood to the surface and caramelizes them; the more heat the more caramelized sugars and flavors. For whiskey and strong spirits this is advantageous, for wine and other spirits other strategies are used. Clay
I make my barrels by hand and don't have the sophisticated equipment to control exact temperatures in the charring process. I char the barrels by making a fire of white oak scraps, which helps to give even more flavor than just plain heat and then shovel the fire into the barrel and roll it around. I use my experience of aging whiskey, tequila and rum and go for the char which has always worked best for me which is a fairly heavy char. I really only have three chars; light, medium and heavy. At your service Clay Johnston