A study conducted in Australia looked at the effects of different percentages of whole bunch fermentation on Pinot noir and Shiraz wine chemistry and sensory. Whole bunch (entirely or partial) fermentation is becoming increasingly popular around the world as winemakers seek to distinguish their wines from the rest of the pack. The study revealed similar, as well as differentiating results for the two cultivars. In general, the results proved positive, depending on the dosage and the style desired, but did also show an increase in methoxypyrazine levels with increased whole bunch percentages.
Methoxypyrazines, of which IBMP is the most well-known, is responsible for the capsicum character in wines made from cultivars such as Sauvignon blanc, Cabernet Sauvignon, Merlot and Cabernet franc. Whereas they can be seen as a positive in Sauvignon blanc, if in balance with other wine aroma compounds, they are in general viewed as a negative for red wines.
Pinot noir and Shiraz grapes contain negligible levels of methoxypyrazines. Enter material other than grapes (MOG) into fermentations, as is the case of whole bunch fermentations, the situation changes. Stalks (rachis) of grape bunches can contain high levels of pyrazines, so if they are included in fermentations, the pyrazines can find their way into the final wines.
In this study in the case of the Shiraz wines the colour intensity increased when whole bunches were included during fermentation. There were no significant differences between the percentage whole bunch treatments though. Stalky and capsicum aroma and flavour descriptors increased with rising levels of IBMP concentrations, which increased with increased percentages of whole bunches included in fermentation. Tannin concentration and the astringency perception also increased with increased percentages of whole bunches included.
In the case of the Pinot noir the red colour increased with 75% and 100% whole bunch fermentations, with an accompanying decrease in brown tint. A huge positive for this cultivar indeed. As is the case with the Shiraz wines, the perception of capsicum also increased with the rising levels of IBMP associated with increased whole bunches. In contrast with the Shiraz treatments, there was no increase in texture or mouthfeel (attributed mainly to the increase in tannins in the Shiraz wines). Interestingly enough, the “cooked vegetable” aroma decreased with increased whole bunch proportions.
This study demonstrates the advantages of doing partial or even entire whole bunch fermentations on these two cultivars, but like everything winemaking (and in life for that matter) it’s a question of finding the balance, since the sensory threshold for methoxypyrazines is extremely low and detecting them in Pinot noir and Shiraz can influence the quality perception of the wines.
Reference
Martin Day and co-workers. Going green with whole bunches. AWRI Report. Wine and Viticultural Journal, Autumn 2020.
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