During the life of the tree, the Spring wood provides the nutrients for the next year’s growth and is what we refer to as grain. It is through the grain’s cellular structure that continuous penetration of oxygen occurs, releasing extractable phenol compounds which interact with the wine and influence the aromatics and the structure.
Toasting causes interactions with these compounds; cellulose, hemicellulose, lignin, tannins, and oak lactones. The toast controls the concentrations of these compounds.
When heated, hemicellulose caramelises imparting notes of brown sugar, caramel, or toffee. With Lignin, the more a barrel is toasted, the more it adds warmth and cinnamon notes. Oak lactones are responsible for the woody/coconut flavours, the longer the toast, the less of an impact. Tannins influence bitterness and mouthfeel, most of the more harsh tannins are removed during seasoning.
Generally for our French and Hungarian oak barrels, and especially for medium-bodied wines, we do not recommend toasted heads. For our American oak barrels, toasted heads are strongly recommended to balance the impact of Quercus Alba.