Colour in Pinot Noir wines: does climate have an impact?

Abstract

Climate change is an increasingly important issue that will affect agriculture, with increasing temperatures being one of the most noticeable impacts. Viticulture is particularly sensitive to climate change, since climate forms a key part of the terroir of a vineyard or a region. In particular, Vitis vinifera L. ‘Pinot Noir’ is known to be sensitive to the temperature in which it is grown, and does not grow well in hot climates. Consequently, a trial was run over two years in a commercial vineyard near Lenswood, in the Adelaide Hills region of South Australia, to determine the impact of higher temperatures on the Pinot Noir grape and wine colour. The study used a passive over-the-vine heating system, which had previously been trialled in the Barossa Valley, South Australia. As expected, the study found that elevated temperatures had decoupled the accumulation of sugars and anthocyanins in grape berries, with the heated treatment grapes producing lower anthocyanin levels than the control treatment grapes per gram of total soluble solids. The temperature effect was less defined for the wines than for the grapes, with the wines from the heated treatment vines having higher total phenolics, and perhaps as a consequence lower CIELab b* values (i.e. less blue pigmentation). Two small scale fermentation trials were also undertaken. One investigated the use of Bodum coffee presses for small scale, replicated fermentations. It also examined whether the position on a slope would influence wine colour and hence be a confounding factor for studies that examine wine colour. It found that the coffee presses functioned satisfactorily as fermenters, and that location on a slope is not necessarily a confounding factor. This latter finding in particular strengthens the results of the vineyard heating trial detailed above, where this was a potential confounding factor. The second fermentation study examined the effects on wine colour of inclusion of stems in ferments, a popular if controversial technique for Pinot Noir. As expected, wines made using stems were higher in tannins and darker in colour, appearing more brick red than wines made without stems. Finally, inductively coupled plasma mass spectrometry (ICP-MS) and nuclear magnetic resonance (NMR) spectroscopy metabolomic techniques were used to characterise a variety of Pinot Noir wines from selected southern Australian wine regions, with wine from Central Otago, New Zealand, used as an out-group. ICP-MS showed promise in determining regionality in Australian and New Zealand wines, with rare earth metals proving particularly useful. NMR analysis of metabolites was less useful, but may be informative for studies of winemaking and viticultural techniques. NMR was expected to be able to distinguish between vintages, but this was not achieved.