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A Technical Guide for Wine Producers
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WINE IN WOOD AND WOOD IN WINE
The influence of toasting and particle size on the flavour contribution made by the use of alternative wood products in vinification
by Charl Theron, guest lecturer in Oenology, Tim Rypstra, professor in Wood Science and Jan Swart, director: Wood and Fibre Institute, Stellenbosch University
It is common knowledge that the toasting of barrels has a very important influence on the flavour impact of the barrels on wine. More than 200 oak based volatile components have been identified. In a previous article the contribution of certain flavour components was discussed. In the case of alternative wood products different factors play a very important role, and other physical aspects that are not applicable when using barrels, merit consideration. The size and dimension of alternative wood products differ considerably and should be taken into account, inter alia, when toasting such products.
Last year Tarac Technologies of Australia launched a new range of alternative wood products known as OakEX. This was the result of a research project to develop the best toasting practices for alternative wood products in order to create a volatile oak profile similar to that of barrels. A unique toasting process was developed for such products. Oak staves are stacked in such a way that free movement of air may occur between the staves. Warm air is used for toasting and consequently a temperature gradient occurs across the thickness of the oak staves. Seeing that temperature influences the formation of various volatile oak components, different flavourants will occur on the different levels of the toasted stave. The toasted stave is then sold as is or in the different formats of alternative products such as mini staves, cubes or chips. Alternative products are usually toasted only after the particular format has been produced. It goes without saying that there is a much larger variation in the composition of such products, compared to the method used by Tarac Technologies. Since warm air is also used for their toasting process, there is more control over the formation of the guaiacol products that impart unpleasant smokey characters. The sensorial characteristics that are usually obtained by using their products are cinnamon, spice, sweet oak and vanilla, which occur in considerably higher concentrations than in other competitive products.
A recent project aimed to:
The extraction period of volatile components
Oak remained in contact with wine for periods of one, two and four weeks and the extracted concentrations of the components were determined using a gaschromatograph. Most of the components were extracted during the first week and the extension of the contact period to four weeks had little effect.
The influence of toasting on flavour extraction
Different toasting methods of oak had a huge impact on the spectrum of flavour components and the concentrations thereof that are formed during toasting. Winemakers should take note of this and be aware that a standard dose of various alternative products will not have identical results.
The influence of the particle size of the product on flavour extraction
Three different particle sizes, namely powder (less than 1 mm), small chips (1 to 5 mm) and normal chips (5 to 10 mm) were investigated. The particle size has a widely divergent influence on the extraction of flavour components from oak. The origin of the oak, be it French or American, also plays a significant role and more research in this regard should be done (Obradovic and Kinley, 2007).
Taking the above into account, winemakers should realise the importance of purchasing such products according to specifications and not at random.
Reference:
Obradovic, D. & Kinley, S. 2007. Time, toast and size: Putting oak alternatives into perspective. The Australian & New Zealand Grapegrower & Winemaker, April 2007: 67 - 72.
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