Winetech Technical Yearbook 2022

MATERIALS AND METHODS Sauvignon blanc (Stellenbosch) and Chenin blanc (Breede River Valley) wines were exposed to several sparging regimes. The wines were made according to the respective wineries’ standard practices and were considered bottle-ready at the time of collection. The experiments were conducted in four custom built stainless steel tanks with a 65 L capacity each. Inert gas sparging was done using two types of gas; 1) nitrogen (N 2 ), and 2) a mixed gas consisting of 70% N 2 and 30% carbon dioxide (CO 2 ). General settings (applicable to all experiments unless specified otherwise): • Before sparging with inert gas, the dissolved oxygen concentra tion of the wines was increased to 3 mg/L using medical grade oxygen (99.8%). • Sparging of inert gas was done at a flow rate of 120 mL N 2 /(L of wine/minute). • Sparging was performed using a 15 μm stainless steel diffusion stone. • Inert gas sparging ceased when the dissolved oxygen concen tration reached < 0.3 mg/L. • The wine was continuously mixed using an automated homo genising mixer during sparging. • Experiments were performed at two temperatures, 18°C and 10°C. Experiment 1: Testing the effect of gas flow rate and wine temperature during sparging The wine was sparged with N 2 using two gas flow rates: There was no significant difference in the rate of oxygen removal when comparing different inert gas flow rates (at either tempera ture tested). The lack of sparging improvement can be attributed to the fact that when applying a higher flow rate (in combination with the mixer) bubbles coalesce and rise to the surface more readily, resulting in less time for oxygen desorption to occur. 3 Oxygen removal efficacy improved as the wine temperature increased. This is in accordance with Henry’s Ideal gas laws where, as the temperature increases, the difference in the partial pressure value required for the expulsion of dissolved oxygen, decreases, resulting in a decrease in gas solubility and faster removal of dissolved oxygen. 4,5 Effect on carbon dioxide content The higher flow rate of inert gas sparging resulted in a greater loss of dissolved CO 2 compared to the lower flow rate (at either temperature tested). The effect of temperature on the carbon dioxide removal needs to be carefully interpreted as the duration of sparging differed between the two tested temperatures. Due to the lower dissolved oxygen removal rate at 10°C, the sparging continued for four minutes longer (extra time needed to reach < 0.3 mg/L dissolved oxygen) when compared to the duration of sparging needed for the wine at temperature 18°C. As a result, the CO 2 concentration in the cooler wine was lower at the end of the sparging duration when compared to the CO 2 content in the warmer wine. Effect on chemical composition There were no significant differences in the free and total sulphur dioxide, glutathione or volatile thiol concentrations, as well as colour measurements between the different treatments under the conditions of this study. • 120 mL N 2 /(L of wine/minute). • 280 mL N 2 /(L of wine/minute). Oxygen removal results

CONCLUSION The inert gas flow rates tested did not differ in oxygen removal efficiency, but it did affect the removal rate of dissolved CO 2 . Lower flow rates in non-turbulent conditions should also be investigated. Oxygen was more efficiently removed when the wine’s temperature was higher. More time and therefore more sparging gas is required to remove the same amount of dissolved oxygen when a wine is at 10°C compared to 18°C. Experiment 2: Testing the effects of mixed gasses during sparging Two types of gasses were tested; N 2 only and a mixed gas consist ing of 70% N 2 and 30% CO 2 . Oxygen removal results Sparging using N 2 gas was more efficient in removing dissolved oxygen when compared to sparging using the mixed gas. Effect on carbon dioxide content Sparging the wine with the mixed gas had varying effects on the CO 2 concentration, depending on the temperature of the wine. When sparged at 18°C, the CO 2 concentration did not change significantly. When sparged at 10°C, a significant increase in There were no significant differences in the free and total sulphur dioxide, glutathione or volatile thiol concentrations, as well as colour measurements between the different treatments under the conditions of this study. CONCLUSION Even though sparging with a mixed gas at higher temperatures was less efficient in terms of removing dissolved oxygen , the re tention of dissolved CO 2 when sparging with the mixed gas is an advantage not obtained when sparging with N 2 gas. It is therefore possible to remove dissolved oxygen, while maintaining or even increasing dissolved CO 2 in wine (effects are temperature depen dent). Sparging with mixed gas can therefore potentially reduce production time as dissolved CO 2 will not have to be replenished after oxygen removal, thereby saving time and resources. FINAL REMARKS It is clear that factors such as wine temperature and gas composition can significantly affect sparging efficacy. In Part 2 of this two-part article, the effects of bubble size, repetitive sparging and extended sparging are reported. ABSTRACT The sparging of wine using inert gas is often used in the wine industry to reduce the concentration of dissolved oxygen in especially white wines. Even though sparging operations are regularly used, there seems to be a lack of information regarding factors that will affect the efficiency of the process, as well as the effect of the technique on the wine composition. REFERENCES https://www.wineland.co.za/factors-affecting-sparging efficiency-part-1/ dissolved CO 2 levels was observed. Effect on chemical composition

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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WINETECH TECHNICAL YEARBOOK 2022