Concept of wood grain
Oak growth is centripetal, meaning that the diameter of the oak's heartwood increases annually. The sapwood, or young wood, is located on the outside. When the wood is cut, one can see areas called rings that correspond to each year in the oak's life. During the tree's development, two types of wood are differentiated. First, the spring wood whose thickness is fairly stable regardless of climate variations; this consists of numerous large, tightly-packed vessels that allow sap circulation.
The second is the summer wood which is denser and formed of small scattered vessels. Its size varies with the oak's growth conditions such as the soil's richness, the density of the stand and the climate. Generally, if growth is fast, the summer wood is thick, if not, it is thin. The grain corresponds to the number of rings in 1 cm of wood. There are generally three categories: fine, medium and coarse.
There is also a genetic factor, as sessile oak tends to have a finer grain than pedunculate oak.
Depending on the grain, the wood's organoleptic properties and permeability to oxygen are likely to be different.