A visiting scientist from China, Dr Bo Teng, has recently completed a successful two-year postdoctoral project at the AWRI.
Bo worked on red wine polymeric pigments and has drafted a manuscript on the kinetics of tannin-anthocyanin reactions, looking particularly at the quantity and stability of the polymeric pigments formed. His main findings were that larger tannins reacted more rapidly with anthocyanin, a trend observed for both skin and seed tannin. The polymeric pigments produced from seed or skin tannin showed different colloidal properties. When seed tannin reacted with anthocyanin, aggregate size increased and precipitation was initiated, resulting in colour loss. However, when skin tannin reacted with anthocyanin, the aggregation-precipitation phenomenon was not seen, and greater levels of polymeric pigment (and colour) were achieved.
This study highlights a potential pathway for pigment loss during winemaking and ageing, which might be managed by preferential extraction of, or supplementation with, skin tannin to stabilise colour early during fermentation. The results also may explain, in part, why wine tannin is primarily derived from the grape skin, and why commercial seed tannin additions neither improve wine colour nor tannin concentration.
Jacqui M.McRae, BoTeng, KerenBindon; Factors Influencing Red Wine Color from the Grape to the Glass; Reference Module in Food Science, Encyclopedia of Food Chemistry, 2019, Pages 97-106; https://doi.org/10.1016/B978-0-08-100596-5.21655-7