Barrel Selection in Wine Making

Barrel Selection

Oak is a crucial and often overlooked component in the world of fine wine. Everything from the type, size, age, grain, and treatment of an oak barrel greatly affects the finished wine. Skills required to construct oak barrels may have been adopted from boat construction centuries ago (Jackson, 2014). The oldest evidence of barrel use for the specific task of aging and transporting wine dates to imperial Roman times, 23-79 A.D (Jackson, 2014). Roman barrels were typically longer and thinner than barrels used today (Ulbert, 1959). Modern day barrels became standard in the early 1500s. Although, barrels with modern characteristics were produced earlier (Laubenheimer, 1990).

The use of oak has been the predominant material of choice since at least Roman times (Jackson, 2014). A variety of other wood choices have also been used, particularly in the construction of fermentation vessels, but have now been made obsolete by the use of inert materials such as stainless steel. The former use of barrels as transporting vessels has now also been replaced by glass bottles or even synthetic bags in the case of bulk wine transport. Oak cooperage is now primarily restricted to the maturation and fermentation of wine. The flavour characteristics, and slight oxidation, imparted from in barrel maturation is believed to enhance the character of wines with distinctive varietal aromas.

Tradition plays a major role in the types of barrels used in a given old world wine regions, compared with a more experimental approach within the new world wine regions. Winemakers from these old-world regions have spent centuries studying and perfecting the selection of barrels of specific characteristics, matching these with specific grape varieties and envisioned wine styles.

Barrel selection characteristics identified of importance include forest origin; wood choice; grain size; cooperage; barrel seasoning; toasting; size and shape; and barrel age. Within this report, each of these characteristics are explained in further depth. These characteristics are summarised from the perspective of two winemakers from separate wineries within the New Zealand winegrowing region of Central Otago. The characteristics are given in context of each of the two grape varieties; Chardonnay and Pinot Noir.

Selection characteristics

The selection of barrels by origin, in particularly forest, is common practice as many of the woos properties are dependent on the geographic origin. Oak tree properties represent both the climatic conditions within the growing region, and the silvicultural practices employed to maintain forest productivity, conditions affecting growth, principally moisture availability, affect wood anatomy and chemistry.

In North America, most of the oak used in barrel construction comes from Kentucky, Missouri, Arkansas and Michigan. There has been little tendency to separate or distinguish oak coming from different states, sites or species. Designation by provenance is traditional in Europe. Geographic designation may include country of origin (e.g. French, German, Russian), region, political district, or forest. The European species Q sessile and Q. robur occur sympatrically throughout much of Europe and species identification is generally possible only using a combination of features, including leaf and acorn morphology.

The predominant wood choice for barrel construction are members of the white oak family Quercus. The species of oak used primarily include Quercus alba, Q. robur and Q. sessile. The two main categories of oak are classed into either American or French (European) oak.

American oak cooperage use predominantly Q. alba and a series of seven related white oaks; Q. bicolor, Q. garryana, Q. lyrate, Q. macrocarpa, Q. muehlenbergii, Q. prinus, and Q. stellata. In Europe, Quercus robur (Q. pedunculata) and Q. sessile (Q. petraea, Q. sessiliflora) represent the primary oak species used in cooperage production. American white oaks tend to have lower levels of extractable ellagitannins than their European counterparts. American oak appears to contain ~40% of the extractable phenolics found in European oaks (singleton et. al., 1971). Although significant differences exist in the levels of extractable tannins between American and European oaks, the intensity of oak flavours is similar, although different in character (Singleton, 1974).

The European Q. sessile has considerably higher levels of extractable aromatics (e.g., oak lactones, eugenol and vanillin) but lower concentrations of ellagitannins, ellagic acid and dry extract than Q. robur (Doussot et. Al., 2000). Q. sessile contains considerably less extractable phenolics than Q. robur (Jackson, 2014). Winemakers desiring higher tannin and phenol levels may choose Q. robur. In areas such as Limousine, winemakers preferring lower levels could use Q. alba, or the mild Q. sessile of Germany. Those preferring intermediate tannin values may prefer Q. sessile grown in France.

Grain size is one of the many factors considered by a winemaker when selecting a barrel for a given wine. As previously mentioned, wood properties represent both the climatic conditions within the growing regions, and the silvicultural practices employed to maintain forest productivity. Conditions affecting growth, principally moisture availability, affect wood anatomy and chemistry. The prevailing opinion  by many is that thin  annual growth rings (fine grained wood) as  a result of slow growth results in higher quality  wood for  use In barrel construction . In an extensive study of Q. robur, and Q. sessile, Doussot et al. (2000) found that grain (ring width) was poorly correlated with either extractable ellagitannins or volatile compounds. However, it has been found that ring width correlates with the wood’s tendency to shrink on drying (Vivas, 2001) and a reduction In the woods permeability of oxygen (Vivas et al., 2003). Both of which are considered significant in characterizing barrel quality.

Slow growth results in less-dense heartwood as a result of a higher proportion of large diameter vessels produced in the spring. in contrast, rapid growth generates wood with a higher portion of small vessels (summer wood). After 10-15 years, sap wood develops into heartwood resulting in the major deposition of tannins (Jackson, 2014). Tannin deposition occurs predominantly in large-diameter spring vessels and as a result growth rate indirectly affects heartwood chemistry. These phenolics contribute significantly to flavour characteristics of a wine during barrel maturation.

Q. robur is often considered to possess a coarser grain (more summer wood and larger growth rings) compared with the finer grain of Q. sessile. This may reflect the growth conditions favoured by the two species as much as the genetic differences. Properties of slowly grown, large -diameter vessel, a sessile, found in forests such as Nevers and Allier are often preferred for the maturation of wine.

There are a range of barrel cooperage techniques employed during the construction of a barrel. Each of which directly impacts the quality of a barrel and the resulting influence and characteristics imparted onto a wine. Coopers often traditionally source barrel wood routinely from specific forests and use specific cooperage techniques ritualistically. This results in distinctive barrel characteristics and a style which is associated with any given cooper.

Barrel seasoning is one of these techniques and varies among coopers. There are two methods of barrel seasoning; natural and kiln dried. Natural seasoned (dried) oak occurs in an open-air environment up to a duration of 2-3 years.

Kiln drying can quickly bring newly cut, green wood, down to the desired moisture content of ~12% (Jackson, 2014). The differences between natural seasoning and kiln drying are increased If drying occurs at both high temperatures and involves the use of newly cut green wood (Jackson, 2014), The drying methods and resulting benefits and consequences are dependent on species (Chatonnet, 1991; Jackson, 2014). An increase in aromatic cis isomer of oak lactone is constantly found with an increase in natural seasoning. Leaching and degradation of phenolic compounds by rain, oxygen, and ultraviolet exposure is significant. Promoting the conversion of the bitter-tasting molecules to its less-bitter product and shows how wood character improves with weathering (Jackson, 2014).

The effects of air drying are also noticeably influenced by the local climate (Francis et al., 1992; Spillman et al., 2004). Due to the variation in the moisture content of air-dried staves and the potential for undesirable fungal development in high moisture conditions, it is now common to combine both natural air drying with kiln drying.

Toasting is a recent innovation (mid nineteenth century). Toasting produces sensory changes in the characteristics of the wood, resulting from pyrolysis. Pyrolysis being the thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. The degree and desirability of pyrolysis depends on the style and characteristics of the wine; and the preferences of the winemaker. Toasting reduces the solubility of oak tannins, particularly useful with European oaks that may possess higher levels of soluble ellagitannins than American oak. Bellow outlines the three categories of toasting; light toast, medium toast and heavy toast (Chatonnet, 1989; Jackson, 2014; Nishimura et al., 1983).

Light Toast

• Temperatures high enough to facilitate stave bending (-5min, inner surface temperatures 100 to 150°C).
• Generates minimal pyrolytic by-products.
• Wood aromatics unmodified: oaky, vanilla and coconut.

Medium Toast

• Temperatures relatively high (-15 min, inner surface temperatures >150°C). Generates phenolic and furanilic aldehydes.
• Vanilla roasted, caramel-like characteristics.
• Preferred with Q. sessilis from Central France by majority winemakers.

Heavy Toast

• Temperatures high (‘°25 min, inner surface temperatures >200°C).
• Destroys/limits the survival of phenolic and furanilic aldehydes within the surface
• layers.
• Increase in volatile phenols; a smoky, spicy aspect.
• Employed with Q. sessilis from southwestern France.

There are considerable amounts of variation between manufactures as no current industry standard exists (Chatonnet et al., 1993). The is also large variation from barrels produced from the same cooperage.

Barrels are produced in a variety of sizes and shapes, dictated by tradition and the intended use. The main barrel types include Bordeaux barrique (225 litres), Burgundy barrique (228 litres), Hogshead (300 litres) and Puncheon (500 litres). Wooden cooperage is primarily used for wine maturation and in some instances, in-barrel fermentation. One of the benefits of a barrel come from the large internal surface to volume ratio (104 cm2/litre for a 225-litre Bordeaux vs. 76 cm2/litre for a 500-litre puncheon). Production economy favours larger size, and earlier maturation favours smaller size. A compromise between these two factors have resulted in the widespread adoption of the Bordeaux and Burgundy barrique. Premium white wines typically receive anywhere from 3-12 months maturation in barrel and red wines 8-24 months, all of which depends of wine style. A study by Perez-Prieto et al., (2003) found that tasters preferred wine aged in smaller oak vessels, those with greater wine to wood ratio (220 litre vs. 500-1000 litre barrels). They also found significant differences in the rate and degree of aromatic uptake, in particular oak lactones and vanillin.

Barrel age, or more importantly the frequency of reuse, directly impacts the amount of total and nonflavonoid phenolic extraction (Rous and Alderson, 1983). The difference in phenolic extraction is most apparent between the first and second fill. The choice in age (frequency) on a wine is on not only the style of wine but also the economics of wine making.

REFERENCES

Chatonnet, P., 1989. Origines et traitements des bois destines a l’elevage des vins de quake. Rev. Oenologues 15,21-25.

Chatonnet, P., 1991. Incidences du Bois de Chene sur la Composition Chimique et les Qualities Organoleptiques des Vins. Applications Technologiques. Thesis. University of Bordeaux II, France.

Chatonnet, P., Boidron, J.N., Dubourdieu, D., 1993. Maitrise de Ia chauffe de brulage en tonnellerie, applications a Ia vinification et a l’elevage des vins en barriques. Rev. Fr. Oenol. 33,41-58.

Doussot, F., Pardon, P., Dedier, J., De Jeso, B., 2000. Individual, species and geographic origin influence on cooperage oak extractible content (Quercus robur L. and Quercus petraea Helot). Analusis 28,960— 965.

Francis, I.L., Sefton, M.A., Williams, P.J., 1992. A study by sensory descriptive analysis of the effects of oak origin, seasoning, and heating on the aromas of oak models wine extracts. Am. J. Enol. Vitic. 43, 23-30.

Jackson, R., 2014. Wine Science: Principles and Applications (Fourth Edition). Tokyo. Academic Press.

Laubenheimer, F., 1990. Le Temps des Amphores en Gaule. Editions Errance, Paris, France, pp. 152— 153.

Nishimura, K., Ohnishi, M., Masuda, M., Koga, K., Matsuyama, R., 1983. Reactions of wood components during maturation. In: Piggott, J.R. (Ed.), Flavour of Distilled Beverages: Origin and Development Ellis Horwood, Chichester, UK, pp. 241-255.

Rous, C., Alderson, B., 1983. Phenolic extraction curves for white wine aged in French and American oak barrels. Am. J. Enol. Vitic. 34,211-215.

Singleton, V.L., Sullivan, A.R., Kramer, C., 1971. An analysis of wine to indicate aging in wood or treatment with wood chips or tannic acid. Am. J. Enol. Vitic. 22,161-166.

Singleton, V.L., 1974. Some aspects of the wooden container as a factor in wine maturation. In: Webb, A.D. (Ed.), Chemistry of Winemaking American Chemical Society, Washington, DC, pp. 254-278. Advances in Chemistry Series No. 137.

Spillman, P.J., Sefton, M.A., Gawel, R., 2004. The effect of oak wood source, location of seasoning and coopering on the composition of volatile compounds in oak-matured wines. Aust J. Grape Wine Res. 10,216-226.

Ulbert, G., 1959. Romische Holzfasser aus Regensburg. Bayerische Vorgeschichtsblatter 24,6-29.

Vivas, N., 2001. Pratiques et recommandations sur la preparation, is mise en service et la conservation de kits neufs et usages. Rev. Oenologues 28 (91), 24-29.

Vivas, N., Debeda, H., Menil, F., Vivas de Gaulejac, N., Nonier, M.- F., 2003. Mise en evidence du passage de I’oxygene au travers des douelles consitivant les barriques par l’utilisation d’un dispositive original de measure de la porosite du Bois. Premieres resultats. Sci. Alim. 23,655-678.