Chapter 21

The Role of Oak in Winemaking

How Wine Barrels Are Made

Wine barrel production is a unique craft, which requires much manual labor, but many of the processes are increasingly mechanized. The process begins with selection of wood. While barrels can be made of many different materials, oak wood is the most common. For barrel manufacturing the wood first has to undergo a series of preliminary processing steps. Traditionally, the coopers (barrel makers) hand split the wood into staves (long strips of wood) to decrease the moisture content of the newly cut wood. Typically, drying of wood takes place outdoors in the open air, but some barrel makers save time and artificially kiln dry the wood.

Staves

After the trees have been harvested the next step is to measure the trunk into usable lengths for the oak barrel staves. These are the narrow pieces of wood that form the sides of any barrel. The wood is split or sawn (depending on whether the wood is French or American) down the medullary (or vascular) rays which run outward from the center of the tree.

Oak Barrel Seasoning

Once the staves have been obtained, they must be seasoned either by natural seasoning or kilning prior to use in cooperage.

Natural Seasoning

Natural seasoning usually lasts between 2 to 3 years depending on the thickness of the staves. Longer drying of wood is usually more acceptable, because shorter drying will add more smoky flavors and astringency to wines. The staves are stacked in the open air allowing the elements (rain and sun) to work its magic on the oak (Figure 21.2). The stacks are usually stacked and re-stacked throughout this period so that the staves on the top one year are at the bottom during the next year, and so on.

Kiln Drying

Kiln drying normally occurs at between 45 and 60 degrees C (113°140°F). It can rapidly bring newly cut (green) wood down to a desirable moisture content - about 12 percent (Jackson, 2008). This technique considerably reduces seasoning time, without altering the oak's physical properties.

Barrel Raising

After seasoning, the oak staves are taken to the preparation workshop, where they are cut to the right length, planed, and jointed as part of their dressing process. Once the staves have been milled, they are assembled using an end hoop that holds the staves into place, the process is often referred to as raising a barrel (Figure 21.3).

Hybrid Barrels

Hybrid oak barrels are barrels that are made using at least two different types of oak. All three types of oak can be used when making a hybrid barrel, although it is less common. The most common hybrid barrels use both American oak and French oak. Hybrid barrels can be made by using one type of oak for the barrel hull and another type of oak for the barrel heads, or by interspersing different oak staves throughout the entire barrel.

Barrel Toasting

In the latter stages of manufacture, barrels are toasted to a greater or lesser degree, i.e., the insides, or maybe just the heads (ends) will be charred over a small wooden fire (Figure 21.4). This stage is considered as the most important because during toasting a chemical modification is induced and new chemical compounds are generated. Another benefit of toasting from the mechanical point of view is that it relieves some of the stress of the newly made barrel, thus reducing the cracking potential of the weak bent staves.

Convection Toasting

Convection toasting uses an indirect heat source rather than direct fire to toast the oak. The heat source heats the air, and the hot air is recirculated from the heat source to the inside of the barrel. The temperature of the hot air can be much lower than that of a wood fire while toasting the barrel in a more uniform manner.

Chiming

Once the barrel has been toasted, it is time for the cooper to adapt the two heads of the barrel. The diameter of these is determined using a compass. The unique aspect of each barrel is further reinforced by these measures, which are never identical for each barrel head. The cooper then uses a tool called a croze to cut the grooves in which the heads, branded with the arms of the cooperage, the year of fabrication and the degree of toasting, are fitted to ensure that the barrel is air-tight.

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