Oak Species and Wood Properties

This year, we will be buying some oak barrels for the fermentation of our Chardonnay and élevage of our red varieties Cabernet Sauvignon and Cabernet Franc. I never feel too comfortable in speaking about a harvest, even before budbreak occurs, but some planning needs to happen in the spring in preparation.
These attributes of an oak barrel make it ideal for winemaking:

• is strong, durable and bendable
• it allows a very slow introduction of oxygen into the wine
• it imparts the character of the wood into the wine

Oak barrels can be made from European and American oak. The various species are:

	American Oak	European Oak
Oak species	Quercus alba and six related white oak species Q. bicolor, Q. lyrata, Q. macrocarpa, Q. muehlenbergii, Q. prinus, and Q. stelata Q. garryanna from Oregon is a new source of oak flavors.	Quercus. robur (Q. pedunculata) Q. sessilis (Q. petraea, Q. sessiliflora)

The preferred part of the oak for barrel making is the heartwood. This illustration shows the location of the heartwood and sapwood.¹

In addition to the heartwood, the type of grain (tight or open), is important in the selection of the oak for barrel making. ).
So how is an oak's grain defined? The grain is defined as the average width between the annual growth rings of the tree. A growth ring is composed of the succession of the spring wood (or early wood) and summer wood (late wood). Spring wood appears richer in vessels, which conduct the sap, summer wood is denser in fibers and parenchyma and fewer vessels.

Open grain has fewer vessels (spring wood) per foot, and more fiber and parenchyma (summer wood). On the other hand, tight grain has a greater proportion of vessels and less fiber material.² Here is where things get a little tricky. Tight grain has more vessels which means that it contains more void, and is therefore more porous!

The tightness or openness of the grain is important because tight grained oak seems more aromatic since more aromas are released from the vessels, where minerals, nutrients, and sugars were located. Conversely, open grain may taste more tannic because the wine gets more contact with fiber material from the larger proportion of summer wood.
Interesting! Much more on oak barrels to come in future blogs.
References:
1. Excellent slide presentation: Barrels & Ageing.
2. Types of oak grain, wine élevage in barrel, Practical Winery & Vineyard, July 2014.
3. Oak Aging and Wine.
4. Boulton, R.B., Singleton, V.L., Bisson, L. F., and Kunkee,R.E., “ Principles and Practices of Winemaking”, Chapman & Hall, New York, 1995, pg. 399.
5. Ronald Jackson, Wine Science Third Edition, Elsevier, 2008.