Effects of elevated temperature in grapevine. II juice pH, titratable acidity and wine sensory attributes

Background and Aims: The effects of vineyard temperature on wine attributes are largely inferred from indirect comparisons between thermally contrasting regions and vintages. Here, we directly assessed wine attributes in trials where manipulation of temperature in the field minimised confounded effects typical of indirect comparisons. Methods and Results: Cabernet Franc, Chardonnay, Semillon and Shiraz vines were exposed to two thermal regimes (elevated temperature, control) over two growing seasons. Juice titratable acidity (TA) and pH, and wine sensory attributes were assessed. Three types of responses to elevated temperature were found for juice TA and pH: (i) pH increased and TA decreased (Cabernet Franc, Chardonnay); (ii) both traits were unresponsive (Shiraz); and (iii) pH increased but acidity was unresponsive (Semillon). Elevated temperature consistently reduced green and citrus aromas, and enhanced rich mouth feel and tropical flavours in Semillon. Thermal effects on sensory traits of Shiraz and Cabernet Franc were strongly season-dependent. Conclusions: Responses of juice TA and pH to elevated vineyard temperature in Shiraz and Semillon did not conform to expectations from indirect comparisons. Owing to confounded environmental factors, the effect of temperature on wine attributes inferred from regional or seasonal comparisons needs to be interpreted with caution. Significance of the Study: Direct evaluation of the effect of elevated vineyard temperature on wine attributes can help develop winemaking adaptations for warmer futures.