All about Barrels

My preference is for fruit before wood. Here's a point of view about the use of wood in wine production that is a little different.

At the outset let us realize that wine is acidic and wood was used for centuries to make wine tanks and vessels for transporting it. Stainless steel is a relatively new innovation. Mild steel and concrete is rapidly corroded by wine and wines stored in steel pick up iron oxide forming a 'casse', a suspension of particles that turns the wine cloudy.

Until very recent years the standard advice given in wine texts was to avoid contaminating ones best wines with the flavour of new wood. The solution was to rinse the barrel with steam or very hot water until wood stain ceased to discolour the water. The second step was to 'condition' the barrel with a lesser wine for a period before using it for ones best product.
Barrels were seen simply as containers and not as sources of flavour.

A marked disadvantage is the difficulty of cleaning barrels through the tiny bung hole. When left empty for longer than a day the barrel would start to 'go off' producing an off flavour from bacterial and mould growth. The availability of affordable stainless steel has meant a great deal to the wine and beer industries.

In 1997 we experimented with 'stackvats' - a container with two wooden and four steel surfaces. "This was a learning experience. The wood was not heated or steamed because it did not need to be bent to the curved shape of a barrel stave. The results were unattractive. Heating the wood is important determinant of the flavour that is imparted to the wine. However, the head of a barrel is not bent and may not be heated by the cooper. We did a lot of work with small cubes of wood subjected to varying heating regimes in an electric pottery kiln then submerged in wine in a 375 ml bottle. Under these conditions oak pickup is fast. After extensive trials we developed a preference for long heating (at least forty minutes), at just short of ignition temperature."

The modern wine industry takes advantage of the flavours of new wood which complexes and contributes to the flavour of wine. This contribution is more or less significant according to the balance between wine and fruit flavours. In lesser wines the wood can make a more important contribution than the grape but the wine is not necessarily improved, despite the expense. In wines of class and real character the wood component, though considerable, may be barely perceptible. Only the grape accounts for palate sweetness and length in wine. The wood, and wood smoke, is capable of heightening and intensifying aromatic sensations which originate in the grape, but it is incapable of producing pleasant flavours in its own right. Married to grapes of quality, wood flavour is a bonus. In the reverse situation its presence is all too obvious and the lack of desirable character in the grape equally apparent.

The choice of barrel size is important in that the ratio between wood surface area and wine volume depends on it. This then determines flavour pick up. It also determines the rate of oxidative change due to absorption of air by the wine. Air is present in the pores of the wood on filling, and gains access via the less than perfect joints between the staves. If a barrel is equipped with a glass end, one can observe minute bubbles of gas covering the entire upper interior surface of the wood. Given the amount of air apparently entering, it is hard to imagine that the wine would survive storage in a wooden barrel. Regular checks of sulphur dioxide content are necessary, especially in warm climates. A rigorous topping regime is desirable to avoid ruinous oxidation. On the other hand, the little bit of air supplied by a barrel will aid in the clarification and tannin softening, especially of young red wines. Wines stored on lees in tanks are always slightly smelly and unfresh by comparison but the same lees are much improved by the oxygen available in a barrel and the wine enhanced by their presence.

Raw wood characters, as one sees them in the aromatics of freshly planed timber, are harsh and unattractive in wine. Barrels must be heated in order to bend the staves without cracking them and in the process the wood is to varying degrees cooked and smoked. Smoking adds inviting aromas to many foods apart from wine. The heating process changes greatly the compounds present in the wood, dries out the cells, shrinkage and weight loss are quite marked, and the flavours change dramatically. Vigorous toasting at high temperatures can actually seal off the cells and delay, perhaps prevent, wine penetration into the wood. The tars present in wood, mobilized by heating, may be the sealing agents. The flavours of charred wood as seen in whisky are not as attractive in wine, as they add an acrid aromatic which may completely dominate. Thus, there's a balance to be achieved between the flavours of unheated wood and those produced by extremes of heating. This balance is not easy to reach in all surfaces of a barrel because of the awkwardness of barrel shape and variances in fire intensity. As noted earlier. the heads, which do not need to be bent, may not be heated at all. Barrels from the same cooper produce variable flavours and it appears that coopering differences are the major source of this variation rather than variations in the wood itself. Because the winemaker is not in a position to relate these flavour differences to what actually happened in the cooperage process, progress in understanding these relationships has been slow.

The price of imported wooden barrels is in excess of $1200 per unit and their use is less and less justifiable as competition drives wine prices ever lower.