Winemakers are continuously frustrated by it. More words are spoken about it than any other aspect of their trade. They whinge about it endlessly, but in some ways without it their jobs would be as interesting as being a dentist. I'm talking about oak, and specifically oak barrels.

Why the complaints? Every now and then the winemaker senses that they have nailed a near perfect match between their fruit and the oak that they have selected. Taste the wine and like the dual Rings of Shazzam, sparks fly. It just tastes right.

Herein lies the problem. The following year, the winemaker will enthusiastically order barrels made from oak sourced from the same forest, and made by the same cooper using identical specifications to the year before. Same result you would think. However to the chagrin of the expectant winemaker the same level of success is rarely achieved.

So what is the reason for this frustrating lack of consistency? The answer is simple. Like every clod of vineyard soil, or every parcel of grapes, each and every oak barrel is unique. No two have ever been the same, and no two ever will be. For just like wine itself, oak is a natural product. The characters that the barrel imparts to a wine are both a reflection of the natural environment in which the tree had grown, and the skill and judgment of the cooper charged with manufacturing the barrel.

Oak used in winemaking is typically produced from trees of three different species. These are the American White Oak, Quercus alba, and two species of European origin, Quercus sessilis and Quercus pedunculata. The latter species is primarily confined to the Limousin forest located a short distance due east of Bordeaux. As a result of the relatively warm, dry and rocky growing conditions experienced by the trees here, Limousin oak tends to be very coarse in grain, and is therefore not preferred by winemakers. Most of this oak is ends up being used to age Cognac and Bourbon.

Quercus sessilis is a tree found throughout central and eastern Europe. In France it is generally harvested from the north eastern forest of Vosges, and the central forests of Allier, Never and the most beautiful of all, Troncais. (Incidentally, it has been reported that the Troncais forest was planted at the order of Napoleon to serve as a future source of timber for his warships. An interesting move given that by the time they reached harvesting age, nuclear submarines ruled the waves!).

Every barrel consists of dozens of individual bent planks of wood called staves. While each stave (theoretically) was harvested from the same forest, individual staves would have almost certainly originated from a tree located in a different part of the forest and from a different part of the tree. Oak trees undergo a growth spurt each Spring. Under favourable conditions, the rate of growth is hastened, leading to a coarser grained wood which is reputed to offer coarser tannins and less subtle oak characters. So logically, each barrel is constructed from a menagerie of oaks with varying grains, each of which offers something different to the wine.

After the oak is harvested it is split into staves and left to dry in stacks for a period of one to three years. The position of each stave in the stack will affect its moisture content at the point at which it is used in the construction of the barrel. The moisture content of the staves impacts on the effectiveness of the next barrel making step, toasting.

Toasting is the step which probably results in the greatest variability in oak barrels. Toasting involves placing the barrel over a flaming pile of oak off-cuts. The intensity of the flame and the time which the barrel is exposed to it fundamentally affect the chemical composition of the oak and hence the flavours that it imparts to the wine. No formulas are applied here. The cooper will use his or her judgment to deliver a level of toast specified by the winemaker, i.e. light, medium, medium plus or heavy toast. The amount of toast and the depth of toasting experienced within the stave depends on the heat of the flame, how long it was applied and the moisture content of the stave. The cooper's judgment of these factors as well as their personal opinion as to what actually constitutes the winemakers specifications can result in significant variability in the end result delivered to the winemaker.

So barrels are as individual as the wine itself. As a result of winemakers' demands, most of the larger barrel manufactures are investigating ways of reducing the variability of their product. Homogenisation is the new philosophy underpinning barrel production. But what will the winemakers have to agonise about then?