Scorching staves

Scorching staves in order to curve them is an important operation, but is seldom considered in enology.

This scorching is not restricted merely to changes in surface colour but also, from what we have observed, affects a 50-cm length of the inside face of the stave and a thickness of 2 mm.

Despite the elasticity created by the heat, the stave acquires folds (under the effect of the curving strain), which can leave cavities 1-2 mm below the surface with a length of up to 5 mm and a maximum gap of one millimetre. On the scorched face the strain of curving may also create exfoliations in the direction of the grain.

It is also quite logical to think that the change would be important with the heating of the vegetable elements causing a change in the anatomy. Folds and hollows are created which make the subsequent asepsis of the wood difficult.

So scorching implies a change in the texture of the oak which is in contact with the wine as well as an alteration in its elements through heating that may affect the quantity and quality of any transfer from the oak to the wine.

Experimental contribution

We kept Rioja white wines in contact with split staves of oak, some scorched normally and others scorched and planed in the burnt zone until the oak was clean.

One month later the wines underwent a study based on various parameters.

Colour change

• Control wine
• Wine in scorched staves
• Wine in unscorched staves

The white wine which was kept in contact with the scorched oak intensified in colour.

	Color	Yellow	Red
Control wine	2,42	1,30	1,62
Wine in scorched staves	2,87	1,60	1,17
Wine in clean staves	8,00	1,40	1,60

Colour increases when the wine is in contact with scorched staves, but no increase of tannin is evident, so there is no harshness of taste.

Alteration of wine residues

After the casks are emptied they are aired for two days and then washed with two litres of water. This water is later used to determine possible oxydisation of the wine in the wood. In scorched staves the level is 0.1 gm/l. and in clean ones 0.28 gm/l. demonstrating that scorching provides more resistance to residual wine.

Taste with scorched oak

This test was carried out in a laboratory, using oak samples of 10 x 5 x 2 cm, scorching them laterally and filling them with Rioja red wine of the 1985 vintage to a volume of 500 cc, hermetically sealed and tasted after ten days:

Tasting of wines in contact with scorched oak
Asturian oak	Taste and aroma defined by winetasters as "arpillera".
Allier oak	Slight contribution of indefined taste.
Limousine oak	Smooth taste similar to "arpillera" or "grasa".
Nevers oak	Very light, strange taste.

In summary it is very interesting to have found the reason for the taste of "arpillera" in certain wines. We have occasionally found a taste definable as "arpillera", even "grasa" in some wines. The reason is an excess scorching of the oak in new casks.

Inter-relations between air, oak and wine.

Our knowledge of these inter-relations is as yet imperfect. We can give them a structure based on studies carried out by various researchers and by ourselves. The oak is a barrier between wine and air.

• Passage and microdiffusion of atmospheric air through the oak into the wine.
• Transfer from oak to wine of:


• Lignin
• Polyphenols
• Enzymes:


• Glycosidase
• Tannase
• Pepsidase
• Polyphenoloxidase


• Diffusion of wine into the atmosphere through oak.

For example, with sawn staves all these functions would be intense but with split staves they would be attenuated.

Preservation variables

• Atmospheric humidity
• Degree of exposure to wine of the casks

The role of alcohol

Alcohol in wine acts in the following ways:

• Hydrolysing lignin in the oak and giving an aroma of balsam.
• It extracts non-flavinoid polyphenols (acids and aldehydes) of the benzoic and cinnamic series.
• It extracts hydrolysed tannins, giving gallic and elagic acids.

This elagic acid released by oak into the wine helps prevent the existence of microbes.

Colour retention

The retention of anthocyanins of red wine in different types of wood has been studied with their subsequent removal through liquid.

Wood	Sawn cut	Split cut
Oak	++++	++
Alder	+++	+
Chestnut	+++	+

This demonstrates that new sawn oak extracts the red colour from a red wine but the majority of this can later be removed from the wood by washing with water.