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A Technical Guide for Wine Producers
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Differrent sources of wood in the wine industry
Charl Theron
Wooden barrels have traditionally been used as containers and the role played by barrels in the extraction and development of flavour and taste components in wine and other products has resulted from this practice. The cost of new oak barrels has increased to such an extent, however, that from an economic point of view it can only be used for premium wines. The cost aspect makes sense if one takes into account the fact that only 20% of a hundred-year-old oak tree can be used for barrels.
It is not only the under-utilisation of the oak tree that comes into play. After two years' usage only about 5 mm of the wood on the inside of the barrel's dowels have been penetrated by the wine. This implies that approximately 80% of a barrel's wood is used for the strength of its contruction and only 20% for its contribution to the quality of the wine (2).
The cost of a barrel is not the only factor that inhibits its use - the same applies to the lack of uniformity (1). The varying use of an open fire in the composition of a barrel, grain density, drying period and wood species are some of the factors that ensure differences among cooperages. The variation among barrels from the same cooperage further confirms the extent of the unpredictability of new oak barrels.
The above-mentioned factors have contributed to the usage of alternative wood products. By definition alternative wood products constitute any wood not coopered in a barrel shape (2).
Innerstave offers the following alternative products, for example:
Nadalie offers different measurements of staves that may for example be toasted on both sides.
Most suppliers offer a wide range of alternative products in varying sizes from powder to staves. Powder and shavings are mostly used during fermentation, while the "oak-chain" and other products are mostly used for and during maturation. It is best to add powder at a dosage of 500 - 700 g per ton to the crusher, so as to stabilise the colour of red wines at an early stage.
It is difficult to determine the amount of wood that will be acceptable. The smaller the wood particle, the more wood will be extracted from it. The mere addition of wood character to the wine does not imply maturation; however, the effective use of micro-oxygenation might address this problem.
Although the higher cost of barrels will remain a reality, it is possible to limit the variability of individual barrels. One way of doing so is to manage the toasting temperature. The colour of the wood is definitely not sufficiently indicative of the degree of toasting. This has resulted in the concept of "Profiling", by which the toasting temperature and period of toasting are used as a basis to ensure repeatability of the process.
During the toasting of barrels extensive physical and chemical changes occur to the wood components. Moreover, a temperature gradient is created by the thickness of the barrel dowel, which may therefore have different flavour implications for the wine that is maturing in it.
The toasting temperature can be defined as low, medium or high. An increase in toasting temperature increases the fullness of the flavours emanating from it. For example, lactone, vanillin and the so-called smoky character are mostly formed during moderate, moderately high or high toasting temperatures respectively. However, the detectability of the different flavour components differs considerably.
The logical question is obviously what constitutes the difference between the traditional and so-called "Profiling" methods of toasting. By using heat sensors and time control the latter process is not quite as arbitrary and therefore also easier to repeat. Once a winemaker has decided which flavours are preferable in his wine after wood maturation, a decision may be reached about the toasting technique with regard to temperature and period.
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