Types of Oak Grain, Wine Élevage in Barrel

WINEMAKING Tools to manage élevage: barrel grain analyzed over time

ABSTRACT Types of oak grain, To choose the proper grain in barrels, it is crucial to understand the defini- tion of grain types and how they in- wine élevage in barrel teract differently with wine over time. Grain is defined by the average width BY Guillaume de Pracomtal, Marie tree. Trees grow outward, from the heart of annual growth rings on a tree. A Mirabel, Rémi Teissier du Cros out to the bark, adding a layer every growth ring is the succession of spring and Anne-Charlotte Monteau, year just under the bark, in the “cam- wood and summer wood. Spring Chêne & Cie (Taransaud, Canton and bium” area. This incremental layer is wood appears richer in vessels, which Kadar cooperages) called the “annual growth ring.” The conduct the sap. The composition of grain is the sum of annual growth rings summer wood is denser in fibers and added each year in the life of a tree. Oak parenchyma. This observation would inemakers always wonder belongs to the family of the “ring explain why tight-grain barrels tend how different types of oak porous” hardwoods. to taste more aromatic (more vessels) grain will interact with When looking under a microscope, a and open-grain barrels give more W their wines. To answer this, ring is composed of the succession of the structure (more fibers). we need to define oak “grain,” which is spring wood (or early wood) and sum- A study by Chêne & Cie R&D further sometimes misunderstood. mer wood (late wood). corroborates this link. The same wine We also need to take a detailed look at Vessels in spring wood are numerous was analyzed over time in tight- and élevage, what happens to the wine dur- and wider than in summer wood. This is medium/open-grain barrels. The study ing time in barrel. In other words, which because spring is when the tree starts shows that tight-grain barrels release a oak compounds are released, modified pumping the sap up its trunk to form greater quantity of wood aromatics (eu- and combined—and how does grain the buds and leaves. Then, in summer, genol, whisky lactones), whereas open- impact these compounds? the leaves use the sun for photosynthe- grain barrels release a larger amount of sis by the chlorophyll to create sugars/ tannins (ellagitannins). Grain (re)defined saccharides, which are stocked in the Over 12 months, patterns of release When we say “tight/fine grain” and tree’s fibers. Summer wood therefore of compounds were different. Tight- “open/wide grain” for French oak, what has a higher density of fibers and paren- grain barrels release greater levels of do we mean? chyma and fewer vessels. wood and spice aromatics in the later Grain is defined as the average width Spring wood is relatively constant in months. Open-grain barrels release between the annual growth rings of the width. The width of summer wood var- 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 concentration of tannins decreased after eight months in all barrels, as tannins polymerize. Wood tannins (ellagitannins) combine with grape tannins (polyphenols). This combination contributes 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.

Pho ies due to the tree’s growing conditions: t o by T primarily climate (rain, sun), but also

a the nearby tree population (height, r a ns shade), properties of the soil (drainage, a ud clay vs. rocks) and terrain (hilltop, slope and creek). Grain is defined as the average width between annual rings.T op: open grain. Bottom: tight grain. This variable thickness of summer (Scale is in centimeters.) wood is what defines grain type. Chêne

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a pre-conceived idea that open grain is more porous— it is actually the opposite. This observation is no doubt counter- intuitive for many of us, but it is crucial in properly understanding the differences in oak grain types. It explains why tight grain seems more aromatic: More aromas are released from the vessels, which makes sense as this is where the sap was with minerals, nutrients and sugars. Our observation also explains why open grain feels more tannic: The wine gets more contact with fiber material, as there is a larger proportion of summer wood. With respect to air exchange, several Pho studies have shown it is difficult to draw t o by T a conclusion as to whether or not grain tightness influences evaporation loss and a r a

ns oxygenation from the barrel. a

ud The higher porosity of tight grain does not appear to allow more air exchange. It Microscopic view of structure of French oak grain showing early/spring wood and late/summer wood. would seem that the air permeability of a barrel is more complex, and less influ- & Cie defines tight grain as less than an has fewer vessels (spring wood) per foot, enced by grain than by several other average of 3 mm per annual growth ring and more fiber and parenchyma (summer wood anatomical factors (such as tylosis (spring wood + summer wood); larger wood). Vice-versa, tight grain has a filling the wood vessels or orientation of than this is open grain. greater proportion of vessels and less medullary rays on the stave). fiber material. Porosity can be misleading The fact that tight grain has more vessels Over time, compounds are extracted When looking closely at the end of a bar- means that it contains more void, and is from grain types differently rel stave, one can observe that open grain therefore more porous, which goes against During barrel aging, a complex exchange

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between barrel and wine occurs. It can be summarized by three main actions: 1. Some aromatic compounds from oak are released into the wine. 2. The wine perfects its structure and texture with the support of oak tannins. 3. Hopefully, the wine acquires balance, notably through the very slow oxygen source: T exchange allowed by the barrel. How do different types of grain influ- a

r ence these three actions? a ns A study by the Chêne & Cie research and a ud development team corroborates the main Schematic view of a section of two growth rings. Early wood—or spring wood—contains more and larger deduction above, and shows that tight vessels. Late wood—or summer wood—contains more fiber and parenchyma. grain releases more aromatics and open grain gives more tannins. The R&D team analyzed the same wine aged in tight-grain and medium/open-grain barrels (30-liter barrels to accentuate the wood impact).* This study showed that the wine evolved differently over time in oak barrels made from two different types of grain. One main conclusion of this study was that tight grain

source: T releases more aromatic compounds over time than open grain (eugenol, whisky lactones), and open grain releases more wood a r

a tannins (ellagitannins). ns

a Looking at the quantity of compounds ud released over time, it appeared that some Schematic view of the side of two staves. The open-grain stave has more fiber (brown), and the molecules were released in the wine very tight grain stave shows more vessels (white circles). early on, in the first months of barrel Think Grandly Canton, Since 1939

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Guaiacol content/Percepon threshold 4 Methyl-2,6-DiMeOphenol (ug/L) Open Grain Tight Grain Vanillin content/Percepon threshold 18 Open GrainTight Grain 25 Open GrainTight Grain 16 2.0 14 20 12 1.5 10 15 8 1.0 0 73 119 253 340 6 10 0.5 4 2 5 0 0 Aging (days) 073 119 253 340 0 Aging (days ) 0 50 100150 200 250 300 350 400 Aging (days) Figure 1. Open-grain barrel releases more Figure 3. Both grain types release vanillin guaicol. The perception threshold is 75 ug/L Figure 2. Open grain has more phenols that slowly. The perception threshold is 320 ug/L in red wine. Vertical axis shows ratio between reinforce toast perception. 4 Methyl2,6- in red wine. Vertical axis shows ratio between the measurement and the perception thresh- DiMeOphenol acts in conjunction with other the measurement and the perception threshold in ug/L. Aromatic descriptors often associ- aromatic compounds, to reinforce the toast old in ug/L. ated with guaicol are wood fire and fireplace, perception. It can also be associated with and it contributes to flavors of roasted coffee. aroma of India ink. different impacts from successive layers. These layers help explain the different aging (such as phenols, furanes and guai- crossing this analysis of compounds phases during élevage. acol), and others only started to appear in released over time with the grain parame- significant quantities after a few months ter, we can analyze élevage along several Three layers may be distinguished of élevage (vanillin and eugenol). key dimensions: concentration of a given in an oak stave: Another study by the Chêne & Cie R&D compound, time spent in barrel and grain The first layer is particularly rich in aro- team showed that these differences in the type. The layers of the stave help classify matic molecules created by the toasting timing of the impact can be explained by the aromas into different groups. process. For example, analyses showed how wine soaks into the oak stave. (Anal- that the concentration of guaiacol in wine ysis for five different toast levels, on 10 Wood layers release increased for the first 75 days in the barrel barrels each, at three different layers, up different aromatics and peaked around that time. After that to 9 mm deep in the wood.) Toasting mostly impacts the surface of peak, the concentration decreases (see Over time, wine soaks into the stave and the stave. As you go deeper in the stave, Figure 1). reaches progressively different layers. the wood has been less transformed by This trend could be explained by the Generally speaking, during the élevage the fire of the toast. One could compare fact that guaiacol comes from thermal wine slowly soaks about 3–4 mm deep this process with the cooking of a steak. degradation of the cellulose of the wood (about 1/8 inch) into the oak stave. When As wine soaks into the stave, it will get during the toasting process, which occurs on the stave surface. More guaiacol is therefore released during the first months Different aromatic compounds are released as the wine soaks into the surface of the as wine soaks into the stave stave. Then some compounds disappear. This trend of release of guaiacol is the ■ First layer releases toast aromas same in both grain types, but the concen- source: T tration was more important for the open- ■ Second layer releases spices, pastry grain barrel, especially at the peak. The

a difference between grain types appears to r a ■ Third layer releases fresh oak aroma ns come from the fact that open-grain wood a ud has more fiber material, more cellulose, and therefore releases more guaiacol. Impregnation of barrel staves by the wine. Something similar happens over time

Synchronizing Wine with Wood

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Cis-Whisky lactone content/Percepon threshold Ellagitannins (mg/L) Open GrainTight Grain Open GrainTight Grain Open GrainTight Grain 5 30 30

L) 25 4 25 g/ 20 3 20 15

15 nnins (m 10 2 ta 10 5 1 Ellagi 0 5 050100 150200 250300 350 073 119 253 340 0 0 Aging duration (days) Aging (days) 050100 150 200 250 300 350 Aging (days) Figure 4. Tight-grain barrels release more Figure 6. Open/medium-grain barrels release whisky lactone (associated with fresh wood Figure 5. Tight grain releases larger concen- more ellagitannins than tight grain. In both smell, coconut and whisky) over time. The per- tration of eugenol. The perception threshold grain types, concentration of ellagitannins ception threshold is 74 ug/L in red wine. Verti- can vary, therefore the graph only shows increases after two months, peaks around cal axis shows ratio between the measurement concentration. Aromatic associations are eight months, and then decreases, as tannins and the perception threshold in ug/L. cooking spices and cloves. polymerize. with another phenolic compound created tions: polymerization, oxidation and pre- tannins, scientists also established that by the toasting process, 4-methyl- cipitation as well. The most important is Acutissimin A had an extremely high 2,6-dimeophenol (see Figure 2). The evo- the polymerization, by which tannins anti-carcinogen effect.** lution of these two phenolic compounds from the grape (polyphenols) combine We would like to think this is the can explain why the toast impact can with tannins from the oak (ellagitannins). French coopers’ contribution to the seem very dominant in the first few This combination forms new tannin com- French paradox. Perhaps there is a hid- months the wine is in barrel, especially pounds that contribute to a softer, den attribute to oak tannins and grain, with open grain, and then is tamed down rounder, silkier mouthfeel. beyond being a crucial tool to adapt as the wine ages in the barrel. By polymerizing, tannins lose some of élevage to the specificity of each wine. PWV The second layer would be best charac- their astringency. This is why it is often said * An experiment was carried out with medium- terized by pastry-like aromatics such as that tannins from the oak provide a “coat- toasted, 30-liter barrels made with tight grain and vanillin. Our analysis shows this com- ing,” a softening of the grape tannins. Tan- medium/open grain. The wine was red Bordeaux pound only starts being released in signifi- nin combinations are believed to be a from Margaux AOP. Two barrels per grain type were cant quantity in the wine after 60 days in critical element in the perfection of many filled after malolactic fermentation, and the wine the barrel, once the wine soaks into the gustative dimensions of wine (structure, tex- was analyzed for several compounds at regular intervals during one year of élevage. The wood-wine wood (see Figure 3). Here there is very little ture, density, creaminess and suppleness). exchange was greater in this small barrel because difference between the open and tight grain. Among the new tannin compound the wood contact surface with the wine in a 30L The fresh oak and spice aromatics are families created by this polymerization barrel is 2.3 times greater than for a 225L barrel. likely to come predominantly from a process, one is particularly striking: Acu- ** Dr. Stéphane Quideau at Institut Européen third layer, deeper in the stave. At that tissimin A. It is formed by the combina- de Chimie et Biologie of Pessac, together with other scientists, found that when the oak tannin depth within the stave, the impact of the tion of a polyphenol from the grape vescalagin interacts with phenols in red wine aged toasting process has been much less. The (flavonoid) and an ellagitannin from oak 18 months in barrels, Acutissimin A is created. wood has not been modified as much by (vescalagin). In 2003, scientists estab- In separate studies this phenolic compound has heat and flames. lished for the first time that red wine been shown to be much more effective than The concentration in the wine of cis- aged in oak barrels contained flavono- certain drugs in stopping the growth of cancerous tumors. “DNA Topoisomerase Inhibitor Acutissimin whisky-lactones and eugenol, for exam- ellagitannins formed during aging, and A and Other Flavono-Ellagitannins in Red Wine,” ple, increase after two to three months which were not present in oak or wine Dr. Stéphane Quideau et al., November 2003, and even faster after eight months. In separately. Among these flavono-ellagi- Angewandte Chemie International Edition. addition, the concentration of these compounds is significantly higher for the wine aged in tight-grain barrels (see Fig- ures 4 and 5).

Tannins interact and soften The studies found that open-grain barrels release more tannins (ellagitannins) into the wine over time than tight-grain barrels. We expect this is due to more fiber and parenchyma material being in contact with the wine. But for both open grain and tight grain, tannins released by the oak barrel follow a very different trend compared to other compounds. Their concentration increases linearly between one and eight months, and then decreases after eight to nine The softening of tannins through polymerization. The Acutissimin A family is an example of these months in barrel, as the tannins soften. new compounds formed during barrel aging. This softening is due to several reac-

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