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64 p r a c t i c a l w i n e r y & v i n e ya r d J U ly 2 0 1 4 W inemakers always wonder how different types of oak g rai n will i nteract wit h their wines. To answer this, we need to define oak "grain," which is sometimes misunderstood. We also need to take a detailed look at élevage, what happens to the wine dur- ing time in barrel. In other words, which oak compounds are released, modified and combined—and how does grain impact these compounds? Grain (re)defined When we say "tight/fine grain" and "open/wide grain" for French oak, what do we mean? Grain is defined as the average width between the annual growth rings of the tree. Trees grow outward, from the heart out to the bark, adding a layer every year just under the bark, in the "cam- bium" area. This incremental layer is called the "annual growth ring." The grain is the sum of annual growth rings added each year in the life of a tree. Oak belongs to the family of the "ring porous" hardwoods. When looking under a microscope, a ring is composed of the succession of the spring wood (or early wood) and sum- mer wood (late wood). Vessels in spring wood are numerous and wider than in summer wood. This is because spring is when the tree starts pumping the sap up its trunk to form the buds and leaves. Then, in summer, the leaves use the sun for photosynthe- sis by the chlorophyll to create sugars/ saccharides, which are stocked in the tree's fibers. Summer wood therefore has a higher density of fibers and paren- chyma and fewer vessels. Spring wood is relatively constant in width. The width of summer wood var- ies due to the tree's growing conditions: primarily climate (rain, sun), but also the nearby tree population (height, shade), properties of the soil (drainage, clay vs. rocks) and terrain (hilltop, slope and creek). This variable thickness of summer wood is what defines grain type. Chêne W I N E M A K I N G Types of oak grain, wine élevage in barrel Guillaume de Pracomtal, Marie Mirabel, Rémi Teissier du Cros and Anne-Charlotte Monteau, Chêne & Cie (Taransaud, Canton and Kadar cooperages) BY Tools to manage élevage: barrel grain analyzed over time grain is defined as the average width between annual rings. top: open grain. Bottom: tight grain. (Scale is in centimeters.) PhoTo by TArAnsAud ABSTRACT To choose the proper grain in barrels, it is crucial to understand the defini- tion of grain types and how they in- teract differently with wine over time. Grain is defined by the average width of annual growth rings on a tree. A growth ring is the succession of spring wood and summer wood. Spring wood appears richer in vessels, which conduct the sap. The composition of summer wood is denser in fibers and parenchyma. This observation would explain why tight-grain barrels tend to taste more aromatic (more vessels) and open-grain barrels give more structure (more fibers). A study by Chêne & Cie R&D further corroborates this link. The same wine was analyzed over time in tight- and medium/open-grain barrels. The study shows that tight-grain barrels release a greater quantity of wood aromatics (eu- genol, whisky lactones), whereas open- grain barrels release a larger amount of tannins (ellagitannins). Over 12 months, patterns of release of compounds were different. Tight- grain barrels release greater levels of wood and spice aromatics in the later months. Open-grain barrels release more toasty/roasted aromas in the early months (furanes, guaiacol and phenols), which then decrease. This explains why shorter aging can em- phasize aromas from the toasting— especially in open-grain barrels. The study showed that the concentra- tion of tannins decreased after eight months in all barrels, as tannins po- lymerize. Wood tannins (ellagitan- nins) combine with grape tannins (polyphenols). This combination con- tributes to a softer, rounder palate. As medium/open-grain barrels re - lease more tannins faster, they seem a better match for shorter élevages, or for highly tannic juices in long élevag- es. During long élevages, tight grain will enhance volume and texture of already elegant grape tannins, while offering a wider aromatic palette.