Oak has become such a standard that it's just assumed that wooden wine barrels are made of oak, but this wasn't always been the case. In ancient times, wine was kept in earthenware jars known as amphorae which were fragile and not conducive to transport. As early as 484 BC there are accounts of wine being loaded in large palm wood casks and floated down the Euphrates River for trade in the cities of antiquity. It's believed that modern wooden barrels, made of separate pieces known as staves and held together with hoops, originated in the alpine tributaries of Rhone: The region where wine was first produced north of Italy. Jumping ahead to more modern times—after the San Francisco earthquake of 1906 California winemakers resorted to using redwood for barrels because European oak was not available.

But out of the thousands of different trees, why has oak become so prevalent? Over the centuries, winemakers found that oak has the proper porosity and strength for barrels while imparting vanilla flavors and tannins that aid in the longevity and structure of wine. But not all oak trees are the same.

There are over 250 species of oak (Euquercus). Of these species, there are two general families, red oak and white oak. White oak has a tighter grain more suited for barrels, where as red oak is too porous. And within the family of white oak, only three species have an optimum grain density or porosity that allows wines to extract oak flavors and tannins, allows small molecules of water and alcohol to evaporate through the barrel aiding in the concentration of flavors, yet keeps the larger air molecules out - all very important criteria for barrel aging of wine.

The three species of white oak used are Quercus Sessilis, Quercus Robur, and Quercus Alba. Of these, Sessilis and Robur are found in France, Russia, Hungary, and the Adyghe forest in Caucase near the Black Sea. Alba (American White Oak) is found predominately in the upper Midwest near the Great Lakes. Of these, Alba has the densest grain and thought to be of medium quality for barrels. Where as Sessilis and Robur from French forests are considered some of the highest quality. Since Jarvis uses only the highest quality French oak, we will focus on Sessilis and Robur from forests in France. Most of the French oak is logged from forests in the central and northeastern regions, mainly the Vosges, Nevers, Bourgogne, Limousin, and Troncais forests. Coopers only account for five percent of all oak harvested in France. So, now we've narrowed the forest from 250 species around the world to two species in France. Simple right?

Not so fast, it turns out to be deceptively complex.

Just as grapes are grown in different areas or appellations, each having a distinct flavor influenced by soil composition and microclimate, the same is true for oak forests. Each forest in France, and even sections within the forest, impart slight variations in the oak. These sections are also known as terroir. Now, all oak trees have the same basic compounds, but different terroir influence or vary the proportions, so even the same species from the same forest can have different nuances.

Now to cloud the issue even more, there are two forest management styles used in France; Taillis (Tie~yee) which is a more let-nature-take-its-course growing method, and Haute Futaie (Ote Fut- tay) which requires thinning of the underbrush and removal of weak trees. The French cooperages favor the Haute Futaie method because it produces taller, straighter, healthier trees. Now that the trees have been selected and harvested, the coopers must select which part of the tree to use.

The oak logs have three general parts to them: The center or pith that supplies nutrients to the tree, the heartwood that gives the tree its strength and stability, and the bark that gives the tree protection. Only the heartwood, free of knots and blemishes, is used for barrels. The heartwood has small vessels or tubes that run the length of the log creating the grain of the wood. These tubes become blocked by cells called tyloses, and are part of the natural aging process. The older an oak tree the more tyloses will be deposited in the vessels or tubes, and the less permeable the wood. French oak has a medium amount of tyloses, and because of this coopers have found it necessary to split the log along the natural grain to make the staves. Otherwise, sawing would cut across the grain exposing the ends of the tubes and the staves would be too weak and porous. In comparison, Alba (American White Oak) has considerably more tyloses increasing its density and strength, therefore they can be quarter sawn.

So now that we have the oak logs split into staves, there are two methods for drying the oak to obtain the desired moisture content of sixteen percent: kiln drying and open air-drying. Kiln drying is fast, but it's the less desirable method as the wood still contains high amounts of pitch that adds unwanted or overbearing flavors. The open air method of drying is highly preferred. The rough oak staves are stacked in an open manner and left uncovered to dry and season in the weather. This mellows the intense oak flavors and is more desirable for the aging wine. At Jarvis, we use only the highest quality French oak barrels made from trees between 80 to 180 years old. All of the staves are dried using the open-air method, aged and seasoned from 18 to 24 months. And the barrels are carefully matched to the wine to introduce the best oak nuances for that particular varietal.

In the next article, we will discuss the barrel types, toasting levels, and the flavors and aromas that oak imparts in wine.