The influence of initial phenolic content on the outcome of pinot noir wine microoxygenation

Yi Yang (Billy)¹, Paul A. Kilmartin¹, Rebecca C. Deed¹, Leandro D. ARAUJO²
1 The University of Auckland
2 Lincoln University

Email contact: yyi419[@]aucklanduni.ac.nz

Over the years, microoxygenation (MOX) has become a popular vinification technique to improve wine sensory qualities. However, among the impacting factors reported, only one published study (Cano-López et al. 2008) investigated the effects of initial phenolic content on wines undergoing MOX. The present study aims to establish the importance of this factor and specifically on light-coloured Pinot noir wines.
Two Pinot noir wines with a low (PN1) and high (PN2) phenolic content were sterile filtered after malolactic fermentation and treated with two oxygen doses (i.e., 0.50 ± 0.08 and 2.17 ± 0.3 ppm/day) for 14 days with temperature control at 15oC. Control treatments had no MOX. Afterwards, the wines were aged for 1 month and followed by SO_2 addition (100 mg/L) with the end point determined 4 days later.
The results highlighted the importance of having high anthocyanin content for Pinot noir wines subjected to MOX on colour development. A higher anthocyanin content significantly increased colour intensity and SO_2 resistant pigments in association with a greater increase in polymeric pigments. However, it did not guarantee colour stability, and SO_2 bleaching erased the improvement on colour intensity in all wines. We speculated that improvement of colour stability by MOX would be dependent on acetaldehyde production, forming pigments with the ethyl-bridged covalent bond that is more resistant to cleavage and SO_2 bleaching. In this trials, limited acetaldehyde formation would expect after the removal of yeast with sterile filtration. Regarding tannin composition, MOX accelerated the decrease of (-)-epigallocatechin extension units in both PN1 and PN2. In PN1, the higher oxygen dosage led to the higher formation of tannin macromolecules and significantly lower tannin yield and (+)-catechin extension units, increasing the proportion of tannin terminals units. These could be of concern for astringency perception (Ma et al. 2014). Therefore, MOX should be applied to Pinot noir and other low phenolic wines with caution.

References
Cano-López, M., Pardo-Mínguez, F., Schmauch, G., Saucier, C., Teissedre, P. L., López-Roca, J. M., & Gómez-Plaza, E. (2008). Effect of micro-oxygenation on color and anthocyanin-related compounds of wines with different phenolic contents. Journal of Agricultural and Food Chemistry, 56(14), 5932–5941. https://doi.org/10.1021/jf8006147
Ma, W., Guo, A., Zhang, Y., Wang, H., & Liu, Y. (2014). A review on astringency and bitterness perception of tannins in wine. Trends in Food Science & Technology, 40(1), 6–19. https://doi.org/10.1016/j.tifs.2014.08.001