5.3.1.e Choice of toasting

What are the different toasting options available?

An additional toasting or bousinage is the final toasting of a barrel which helps to enhance the aromas and tannic profile that the barrel will bring to the wine.
Toasting is the aspect over which the winemaker has the most control. Various parameters should be monitored during toasting to obtain very different aromatic profiles.

These values vary depending on the cooper. Toasting can be open or closed. If the toasting is closed, it means that a metal lid is placed on the top of the barrel. Both techniques can be used in the same toasting. Whether a lid is placed on the barrel or not affects the rate at which the temperature rises.

What is the impact of toasting on the wine's aromatic properties?

At an aromatic level, the products of polysaccharide thermo-degradation yield three main molecules: hydroxymethylfurfural (caramel), methylfufural (toasted almond) and furfural (almond). Generally, these molecules are not present in sufficient quantities to be perceived by the majority of tasters (extraction is quite difficult). They can nevertheless bring complexity and the interaction between the different aromatic molecules is far from being established.
Then there are the products resulting from lignin thermo-degradation. The depolymerization of lignin leads to the appearance of vanillin, whose name alone evokes its odour. Pyrolysis reactions occur, which facilitate production of volatile phenols and phenyl ketones. For example, syringyl, which gives spicy, smoky aromas.
Note: the presence of water vapour is used to lower the surface temperature of the inside of the barrel during toasting and favours the breaking down of lignin.
Lastly, the Maillard reactions, responsible for the roasted odour due to three main molecules, cyclotene, iso-maltol and maltol. The cyclotene and iso-maltol content increases with the intensity of the burning.

To summarize, we have five aromatic categories:

• Lactones (wood) coconut, fresh wood, etc.
• Volatile phenols (toast) spicy, clove, smoke, etc.
• Furans (toast) coffee notes, smoked, grilled, etc.
• Vanillin and other phenol aldehydes (toast) vanilla, etc.
• Molecules resulting from burning (Cresol, maltol, etc.) grilled flavours

The proportion of these different elements will depend on the heating time and temperature.

How does toasting affect the wine's organoleptic characteristics?

The heavier the toasting, the more ellagitannins are broken down, as they are heat sensitive. Barrels with less toasting often offer more structure.
However, this must be qualified. More toasting can lead to micro-cracks on the wood's surface, which significantly increases the wood's permeability to liquids. The wine can then penetrate deeper into the wood where fewer ellagitannins have been broken down. There is therefore a significant contribution of ellagitannins in the case of long ageing, but not for shorter ageing periods.
The longer and more moderate the toasting, the more vanillin is created.