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February 2015 practical winery & vineyard 63 w i n e m a k i n g the level of maximum O 2 measured. This corresponds to the results of the recent research by M. Mirabel, also showing that the toast has no effect on porosity. 8 Influence of type of barrel alternative Oak chips are used as alternatives to oak barrels. The previously described proto- col for staves was used to calculate the maximum O 2 for chips. The maximum O 2 levels for staves and chips from the same source are shown in Figure 4. Oak chips, like staves, contain a significant amount of oxygen. However, the level of maximum O 2 for chips is, on average, one-half that for staves. Change in SO 2 level according to different parameters We have shown that the use of oak can supply significant amounts of oxygen. We illustrate this phenomenon by show- ing the change in the level of sulfur diox- ide in an alcohol-water solution in which increasing concentrations of untoasted oak chips were macerated. During this experiment, regular samplings were performed for 32 days (Figure 5). The loss of free SO 2 is quicker and bigger when the quantity of chips is increased. For the model wine with slow growth (1 mm), tight structure for "fine grain." 4 This systematic relation- ship between growth rate, structure and porosity is commonly accepted by coo- perage professionals. We have assessed the impact of certain parameters on the maximum O 2 values measured in the samples: They range from 0.48 mg/L to more than 3.3 mg/L depending on the sample. The detailed analysis of the results (Figure 2A) shows that the selection of wood by grain width is not a criterion that enables them to be classified according to oxygen content. These results are consistent with a 2011 study by M. Mirabel, which emphasizes, among other things, the absence of cor- relation between oak density and grain width. 8 However they contradict the results obtained by Riad Bakour. 1 After analysis of many anatomical parameters of oak (on nearly 290 samples), small but significant correlations were found between grain width, wood porosity and its density. However, our results tend to show that the maximum O 2 value is fairly well cor- related to the density of wood used in this protocol (Figure 3). In other words, low-density wood is likely to supply more oxygen to the solution than high- density wood. We thought the toast might change the amount of oxygen contained in the wood. It is not impossible that toasting of staves could lead to changes in the inter- nal structure, that would likely change the porosity, or at least cause cracking of the vessel walls, allowing the liquid to extract air from the cavities more easily. In order to validate this hypothesis, we used the previously described protocol to compare the maximum amount of oxygen yielded by the oak, whether toasted or not. The analysis of the results (Figure 2B) shows that the toast has no effect on OENOSTAVE fan of twenty 0.28 mm thick French oak staves that are 37.4 inches long and 2 inches wide. 145 Jordan Street • San Rafael, CA 94901 • 415-457-3955 • Fax 457-0304 • www.boswellcompany.com