Oak Barrel Morphology

My previous blog post was about Oak Species and Wood Properties of oak barrels. Today, I'm continuing the oak theme with blogging about barrel morphology and the parts of a barrel.
Here is an illustration of a barrel with all of the various parts labeled:¹

To make a barrel, the oak tree must be at least 100 years old! The trees are usually harvested in the winter or autumn when the sap is least active. The trees must be straight and defect free. Only the portion of the oak from the ground to the first lateral branches is used, which can yield at least 2 and at most 4 barrels. In France, oak forests have been farmed for hundreds of years and grown in a way to ensure the production of tall and straight trunks.

The species of oak and the wood properties play a role in how the staves are made. In oak trees, there are medullary rays that run perpendicular to the growth rings. Medullary rays are diffusion channels or 'tubes' for the transmission of water, sap and nutrients. They are arranged like spokes in a wheel.

American oak contains much more tyloses than French oak and at the intersections with the medullary rays in the growth rings, these rays concentrate tyloses, creating dams. The tyloses in American oak effectively seal up the heartwood and can be quarter sawn as opposed to French oak which must be hand hewn along the lines of the medullary rays.
These specific ways to make a stave, based on the type of oak, ensures that there will be no leakage through the medullary ray.² After the staves are made, the preferred method of drying is in the open air as opposed to the more rapid kiln drying. The staves then have a chance of drying more evenly, thereby retaining the aromatic qualities and leaching out more tannin from the wood.
Who knew that there was so much to learn about barrels and there is so much more to learn! As least my husband and I will be a informed consumers when we go to buy our barrels.
References:
1. Barrels & Ageing
2. Nick's Vintage School
3. How to Evaluate Wood