Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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WINTER 2013
WINEMAKING
If we only focus on the extraction of wood compounds (Figure 3), one can observe that the 7 mm staves contain less than 5% of the initial concentration of wood compounds, while the 18 mm staves contain 2% to 20% of the initial concentration depending on the analyzed molecule.
Figure 3. Percent of extractives of wood compounds into 7 mm and 18 mm staves.
This study shows that during maceration of staves in wine, the wood loses a significant proportion of its extractives. If we consider the amount of wood extractives leached by wine (difference between extractives in wood before and after maceration), we find approximately the same amounts for 7 mm and 18 mm staves taken at an identical dose (10 g/L), a small discrepancy arising only from a slight difference between extraction rates for these two types of staves (Figure 4).
On the other hand, if we consider the dose of staves in percent of surface (example of thin and thick staves), we have almost 2.5X as much equivalent barrel surface for the 7 mm stave than with the 18 mm stave. This means that a winemaker who takes into consideration the contact area would, in practical terms, use a dose of 2.1 staves (7 mm) to reach the result obtained with two staves of 18mm in terms of wood extraction, and must have made a mistake with the
dose. This leads to a very important error as far as oak extraction and enological results are concerned.
Figure 4. Percent of extractives leached by wine from 7 mm and 18 mm staves.
Conclusions
This trial shows that the way of expressing the wood dose for staves in g/L is closer to reality in enological terms than that expressed in terms of contact surface. This result is conditioned by the phenomenon of a very deep penetration of wine inside the stave (in all three directions: radial, tangential, and longitudinal) and consequently by a significant extraction of wood compounds (80% to 95%) during stave maceration; this phenomenon is different to those observed when using barrels.
The use of surface area still makes sense if the winemaker always works with the same type of stave. For example, by doubling the number of staves per hectoliter, he also doubles the surface area.
However this approach is no longer accurate if the winemaker uses different types of staves and in particular staves of different thickness. In this case, the use of the g/L approach is essential and enables the winemaker to avoid making errors of dosage and therefore enological mistakes.
   
References
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