## 3 Results and Discussion
### Evolution of the Concentrations of Cu and SO\({}_{2}\) during Wine Production
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**a,b** **Shiraz** & **Control** & **LCu** & **HCu** & **LSO2** & **HSO2** \\ \hline \multicolumn{6}{c}{_total Cu (\(\mu\)g/L)_} \\ \hline M & \(2007\pm 76\) c & \(10577\pm 412\) b & \(15051\pm 2756\) a & \(1985\pm 70\) c & \(1807\pm 78\) c \\ PAF & \(567\pm 31\) a & \(679\pm 100\) a & \(598\pm 31\) a & \(565\pm 28\) a & \(577\pm 77\) a \\ PB & \(305\pm 34\) bc & \(351\pm 23\) ab & \(278\pm 27\) c & \(331\pm 22\) abc & \(383\pm 60\) a \\
15 Mo & \(272\pm 33\) a & \(189\pm 20\) b & \(142\pm 0\) c & \(188\pm 18\) b & \(212\pm 30\) ab \\ \hline \multicolumn{6}{c}{_free Cu (\(\mu\)g/L)_} \\ \hline M & n/a & n/a & n/a & n/a & n/a \\ PAF & \(59\pm 5\) b & \(62\pm 8\) b & \(131\pm 26\) a & \(39\pm 1\) bc & \(28\pm 3\) c \\ PB & \(40\pm 2\) a & \(31\pm 3\) b & \(22\pm 4\) c & \(22\pm 0\) c & \(34\pm 2\) ab \\
15 Mo & nil & nil & nil & nil & nil \\ \hline \multicolumn{6}{c}{_bound Cu (\(\mu\)g/L)_} \\ \hline M & n/a & n/a & n/a & n/a & n/a \\ PAF & \(508\pm 30\) ab & \(618\pm 95\) a & \(467\pm 14\) b & \(526\pm 27\) ab & \(549\pm 79\) ab \\ PB & \(270\pm 32\) b & \(320\pm 23\) ab & \(256\pm 28\) b & \(306\pm 18\) ab & \(349\pm 58\) a \\
15 Mo & \(272\pm 33\) a & \(189\pm 20\) b & \(142\pm 0\) c & \(188\pm 18\) b & \(212\pm 30\) ab \\ \hline \multicolumn{6}{c}{_total SO2 (mg/L)_} \\ \hline M & 0 c & 0 c & 0 c & \(135\pm 38\) b & \(244\pm 71\) \\ PAF & \(6\pm 1\) c & \(6\pm 0\) c & \(5\pm 0\) c & \(12\pm 1\) b & \(20\pm 1\) a \\ \({}^{\rm c}\) PB (pre-SO2) & \(65\pm 4\) b & \(66\pm 4\) b & \(75\pm 15\) ab & \(76\pm 8\) ab & \(88\pm 1\) a \\ \({}^{\rm d}\) PB (post-SO2) & \(120\pm 8\) b & \(119\pm 5\) b & \(129\pm 6\) ab & \(138\pm 9\) a & \(129\pm 4\) ab \\
15 Mo & \(79\pm 3\) b & \(80\pm 7\) b & \(91\pm 2\) a & \(89\pm 4\) ab & \(92\pm 3\) a \\ \hline \multicolumn{6}{c}{_free SO2 (mg/L)_} \\ \hline M & 0 c & 0 c & 0 c & \(57\pm 17\) b & \(109\pm 36\) a \\ PAF & 0 a & 0 a & 0 a & 0 a & \(1\pm 0\) a \\ \({}^{\rm c}\) PB (pre-SO2) & \(5\pm 0\) b & \(5\pm 0\) b & \(4\pm 0\) b & \(8\pm 2\) a & \(8\pm 1\) a \\ \({}^{\rm d}\) PB (post-SO2) & \(29\pm 10\) a & \(27\pm 1\) a & \(24\pm 0\) a & \(29\pm 1\) a & \(30\pm 4\) a \\
15 Mo & \(23\pm 3\) a & \(21\pm 3\) a & \(21\pm 4\) a & \(25\pm 4\) a & \(26\pm 6\) a \\ \hline \multicolumn{6}{c}{_free SO2 (mg/L)_} \\ \hline M & 0 c & 0 c & 0 c & \(57\pm 17\) b & \(109\pm 36\) a \\ PAF & 0 a & 0 a & 0 a & \(1\pm 0\) a \\ \({}^{\rm c}\) PB (pre-SO2) & \(5\pm 0\) b & \(5\pm 0\) b & \(4\pm 0\) b & \(8\pm 2\) a & \(8\pm 1\) a \\ \({}^{\rm d}\) PB (post-SO2) & \(29\pm 10\) a & \(27\pm 1\) a & \(24\pm 0\) a & \(29\pm 1\) a & \(30\pm 4\) a \\
In Chardonnay at PAF, the concentrations of both free and bound Cu were higher with increasing additions of Cu to the juice (Table 1). Free Cu tended to increase from PAF to PB, while the opposite result was observed for bound Cu (Table 1). A portion of the decrease in bound Cu would be due to the decreases in total Cu, and the increases in free Cu were consistent with oxygen exposure to the wine during the different wine production steps. The oxidation of wine can lead to the dissociation of the Cu-sulfide complexes (bound Cu) and regeneration of Cu(II) (free Cu) [44; 45]. For the Shiraz, the HCu treatment had the highest free Cu concentration at PAF, but by PB, there was minimal difference among all samples. In Shiraz wines, both free and bound Cu decreased significantly (\(p\leq 0.05\)) after the cold stabilization (PB for Shiraz, Table 2). The large decrease in free Cu in the Shiraz HCu treatment may have been a consequence of the high phenolic concentration in the wine sample, leading to faster oxygen consumption compared to the white wine. This would have allowed a low oxygen concentration to be reached relatively rapidly in the Shiraz wine, and hence it favored free Cu in sequestering sulfide from sources in the wine. Low oxygen conditions in wine are known to induce a decrease in free Cu in certain wines [46].