Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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French Oak medium plus toast “Fan Innerstave” is 25.5 inches long, 2 inches wide,
and 5/16th inch thick, from a stainless steel red wine tank at Cline Cellars, Sonoma, CA.
Andrei Prida, Benoît Verdier,
Tonnellerie Seguin Moreau, Z.I. Merpins, Cognac, France
U se of oak wood pieces is a practice by which it is possible to impart a given quantity of oak wood compounds to wines in order to obtain certain enological results, such as enhancing woody flavors, increasing complexity, mouthfeel, and structure. This practice has been legal in Europe since 2006 (Règlement CE 1507/06).
This operation enables winemakers to get the benefits of oak for low- and medium-range wines, which could not be aged in barrels because of the price barrier.
In practice, winemakers introduce wood pieces (chips, fragments, staves, sticks, etc) in stainless steel tanks at different stages of wine processing (in juice before alcoholic fermentation, during malolactic fermentation, or after malolactic fermentation during ageing) for a different duration of maceration reaching sometimes up to 12 months. Depending on the size of wood pieces, sometimes they are attached to the wall of stainless steel tanks, or they are just put into wine in bulk.
The impact of wood compounds obtained from barrel alternatives not only depends on the type of products (size, grain size, seasoning, etc.), origin of wood (French oak, American oak, etc.), toasting (light, medium, etc.), but also on the quantity of wood which is put into contact with the wine. The quantity of oak (dose) may vary a lot according to the type of result required. How to calculate the wood dose differs between the various alternative products.
The dose is generally expressed in g/L for small wood pieces (powders, chips). This approach is commonly accepted and provides consistent results, whereby winemakers find a correlation between the oak intensity and the quantity (in grams) of oak they have used.
In contrast, for big wood pieces (staves), there are two types of wood measuring. One is using the gram/L approach, while the other is the calculation of the area of wood in contact with wine as a percentage of the total volume of wine.
The second approach is linked to the analogy with barrel ageing (elevage). Winemakers frequently talk about the percentage of contact area of the new barrel (or of new wood) to express the dose of oak. Since the internal area of a 225L barrel is about 2m3, 100% of a new barrel is equal to 0.0089 m2/L. In cellar practice, winemakers seldom use a dose equivalent to 100% of a new barrel, but rather 30% to 50%.
What is the base of this calculation? The calculation, based on contact surface, reflects the hypothesis of proportionality of wood compounds migration according to the winewood contact area. The basis of this hypothesis is the very low penetration of wine into wood by its surface. In other words, independently of the wood thickness, the wine will always penetrate at the same (rather low) depth in wood and extracts the same quantity of wood extractives. The experience we have with barrels shows that this is certainly true as far as barrel aging is concerned.
There are two phases in the extraction of wood compounds during elevage in barrels. The first one corresponds to a progressive hydration of wood by wine (approximately four months), while the second one is a stationary phase during which the depth of penetration remains constant. The speed of liquid penetration into wood is a limitation factor for the extraction of wood compounds.3 The depth of wine penetration into wood is about 2 to 4 mm; there are various estimates of such penetration according to the methodology used.
For example, F. Feuillat estimated this layer by measuring the humidity, which was considered as a marker of penetration.2
Figure 1. 18 mm stave used for wine ageing cut lengthwise to expose wood with no wine penetration.
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