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February 2015 practical winery & vineyard 61 w i n e m a k i n g uid-liquid extraction and GC-MS using a previously validated method. Development of method to monitor oxygen supplied by oak wood The quantity of oxygen supplied by oak- wood staves was estimated according to several different parameters. An example of the kinetics of oxygen liberation by a stave in a model solution is presented in Figure 1. In our experimental conditions, this includes three phases: At the first contact between the wood and the solution, the oxygen concentra- tion increases very significantly (Phase 1). More than 80% of the maximum oxy- gen concentration measured (maximum O 2 ) during the experiment is achieved within 48 hours. The oxygen content reaches a plateau lasting two to three days, corresponding to what is referred to as the maximum concentration mea- sured (maximum O 2 ). An equilibrium is therefore established between the oxygen still present in the crevices in the wood and oxygen present in solution (Phase 2). The last phase corresponds to a lower- ing of the oxygen concentration through its consumption by oak wood extractives, which outweigh the extraction kinet- 3,5 3 2,5 2 1,5 1 0,5 0 0,58 0,6 0,62 0,64 0,66 0,68 0,7 Oxygen supply, mg/L Wood density, g/cm3 R 2 = 0.63691 Phase 1 Phase 2 Phase 3 Figure 3: Maximum quantity of oxygen supplied by an un-toasted oak stave placed in a model solution, according to the density (n = 20). 180 160 140 120 100 80 60 40 20 0 Staves Chips O 2 µg/g of dry wood Figure 4: Comparison of the level of maximum O 2 obtained from maceration of the same quantity of oak staves and chips (17 g/L) in an alcohol-water solution (n = 6).