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68 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 I N E M A K I N G Synchronizing Wine with Wood aging (such as phenols, furanes and guai- acol), and others only started to appear in significant quantities after a few months of élevage (vanillin and eugenol). Another study by the Chêne & Cie R&D team showed that these differences in the timing of the impact can be explained by how wine soaks into the oak stave. (Anal- ysis for five different toast levels, on 10 barrels each, at three different layers, up to 9 mm deep in the wood.) Over time, wine soaks into the stave and reaches progressively different layers. Generally speaking, during the élevage wine slowly soaks about 3 – 4 mm deep (about 1/8 inch) into the oak stave. When crossing this analysis of compounds released over time with the grain parame- ter, we can analyze élevage along several key dimensions: concentration of a given compound, time spent in barrel and grain type. The layers of the stave help classify the aromas into different groups. Wood layers release different aromatics Toasting mostly impacts the surface of the stave. As you go deeper in the stave, the wood has been less transformed by the fire of the toast. One could compare this process with the cooking of a steak. As wine soaks into the stave, it will get different impacts from successive layers. These layers help explain the different phases during élevage. Three layers may be distinguished in an oak stave: The first layer is particularly rich in aro- matic molecules created by the toasting process. For example, analyses showed that the concentration of guaiacol in wine increased for the first 75 days in the barrel and peaked around that time. After that peak, the concentration decreases (see Figure 1). This trend could be explained by the fact that guaiacol comes from thermal degradation of the cellulose of the wood during the toasting process, which occurs on the stave surface. More guaiacol is therefore released during the first months as the wine soaks into the surface of the stave. Then some compounds disappear. This trend of release of guaiacol is the same in both grain types, but the concen- tration was more important for the open- grain barrel, especially at the peak. The difference between grain types appears to come from the fact that open-grain wood has more fiber material, more cellulose, and therefore releases more guaiacol. Something similar happens over time Guaiacol content/PercepŸon threshold Open Grain 18 16 14 12 10 8 6 4 2 0 0 73 119 253 340 Tight Grain Aging (days) Figure 1. open-grain barrel releases more guaicol. the perception threshold is 75 ug/L in red wine. vertical axis shows ratio between the measurement and the perception thresh- old in ug/L. aromatic descriptors often associ- ated with guaicol are wood fire and fireplace, and it contributes to flavors of roasted coffee. Vanillin content/PercepŸon threshold 2.0 1.5 1.0 0.5 0 73 119 253 340 0 Aging (days) Open Grain Tight Grain Open Grain Tight Grain Aging (days) 25 20 15 10 5 0 0 50 100 150 200 250 300 350 400 4 Methyl-2,6-DiMeOphenol (ug/L) Figure 2. open grain has more phenols that reinforce toast perception. 4 Methyl2,6- diMeophenol acts in conjunction with other aromatic compounds, to reinforce the toast perception. It can also be associated with aroma of India ink. Impregnation of barrel staves by the wine. Different aroma c compounds are released as wine soaks into the stave ■ First layer releases toast aromas ■ Second layer releases spices, pastry ■ Third layer releases fresh oak aroma source: TArAnsAud Figure 3. Both grain types release vanillin slowly. the perception threshold is 320 ug/L in red wine. vertical axis shows ratio between the measurement and the perception thresh- old in ug/L.