Issue link: http://winesandvines.uberflip.com/i/602988
62 WINES&VINES December 2015 WINEMAKING PRACTICAL WINERY & VINEYARD the real wine measured in the no oxygen- consuming liquid. The measurement technol- ogy and procedures are detailed in a scientific report published in the Journal of Agricultural & Food Chemistry. Annual rate of oxygen entry into barrels Stage two of this study involved measuring DO concentrations during the first 24 hours and for three weeks after filling the 12 barrels (data not shown). The concentrations were not sig- nificantly statistically different between the American and French oak barrels, although concentrations were higher during the first 10 hours for the American oak. No statistically significant differences were observed between the fine-grain and medium-grain American oak barrels, although the fine-grain barrels pro- vided more oxygen to the model wine during the first few hours (del Alamo-Sanza and Ne- vares 2014). To evaluate the overall rate of oxygen entry into wine-soaked oak barrels, the OTR in four fine-grain American oak barrels was analyzed over 12 months. The graph "Evolution of Oxy- gen Transfer Rate" (at top right) shows the OTR (mg/L per day) in the tested barrels throughout the year. Analysis of the cumulative daily intake indicated that the dissolved oxygen in oak bar- rels continued to increase, but at a decreasing rate for the first six to eight weeks (see "Accu- mulation of Oxygen Intake" at lower right). The OTR becomes approximately constant through- out the remaining year of élevage. In addition, the OTR decreased after the first three to four weeks. These results indicated that the actual rate of oxygenation per year is much lower than the rate that would be estimated if measuring only during the first weeks of testing. Therefore, it is important to test the evolution of oxygen entry kinetics for one year. The daily average dose throughout the year was 0.32 mg/L. After the first month of élevage, the fine grain American oak barrels continued to provide the wine with between 0.029 mg/L and 0.038 mg/L of oxygen daily for the remain- der of the year. Based on these results, we calculated the total dose of oxygen that a wine would take up in a fine-grain American oak barrel was 11.62 mg/L per year. These results were significantly lower than results published previously by other authors who measured oxygen entry into new barrels. J. Riberau-Gayon observed an oxygen entry rate of 21 to 28 mg/L per year, 1 and N. Vivas and Y. Glories observed an oxygen entry rate of 20 mg/L per year in two new Limousin coarse-grain barrels from central France. 2 In both of these studies, the sulfate formed from SO 2 in the solution inside the barrel was evaluated at six months. The methodologies of these studies may explain the postulated high rates of oxygen entry by the above authors, given they did not consider the influences of progressively increasing wood moisture content leading to decreasing OTR. The results we obtained also were lower than those estimated by M. Kelly and D. Wol- lan. 8 These authors treated the wood as a semipermeable membrane that allowed for oxygen diffusion according to Fick's law. Based on their calculations, the maximum amount of oxygen that could enter a barrel was 36.4 mg/L per year. However, this approach is erroneous because wood is a porous membrane that does not always function the same way. Specifically, the moisture content of wood can modify its properties and oxygen perme- ability. The Kelly and Wollan study did not assess the amount of oxygen entry into the barrel for an entire year. 8 Instead, these results were obtained from theoretical approaches or extrapolated from six months of élevage data at different times of the year. Based on the annual dose results of oxygen in our four-barrel study, the percentage of daily oxygen intake for each barrel (shown as a The accumulation of oxygen taken up in each studied barrel during one year. The evolution of the oxygen transfer rate (mg/L per day) of four oak barrels throughout one year. 0 30 60 90 120 150 180 210 240 270 300 330 360 Time (days) 16 14 12 10 8 6 4 2 0 Accumulated Dissolved Oxygen (mg/L) Oak barrel 1 Oak barrel 2 Oak barrel 3 Oak barrel 4 ACCUMULATION OF OXYGEN INTAKE EVOLUTION OF OXYGEN TRANSFER RATE Oak barrel 1 Oak barrel 2 Oak barrel 3 Oak barrel 4 Mean OTR (mg/L per day) 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0 0 30 60 90 120 150 180 210 240 270 300 330 360 Aging time (days)