Ripening Speed of Grapes Can Influence Wine Taste

Grapes are strongly influenced by the environment of the vines, and climate change can affect the grape and wine quality. Heatwaves and droughts, for example, can lead to earlier ripening of the grapes. As grapes ripen, sugars as well as phenolic and volatile compounds that influence the aroma of the resulting wine accumulate. Accelerated ripening can lead to wine that has higher alcohol levels and lacks flavor balance. To counteract these negative effects of climate change on wine quality, researchers have investigated how the ripening process can be controlled. For example, reducing the crop on the vines can speed up grape ripening, while more intense irrigation later in the growing season can delay the process.

Christopher M. Ford, University of Adelaide and Australian Research Council Training Centre for Innovative Wine Production, both Glen Osmond, Australia, and colleagues have investigated how the growing conditions of grapes influence sugar accumulation and the production of secondary metabolites that influence the aroma of the resulting wine. The researchers grew Cabernet Sauvignon wine grapes at a commercial vineyard in California, USA. Then, they removed a portion of the clusters on some vines to reduce the crop and/or irrigated some plants more during the later growing season. They also let some vines grow under standard conditions. The team collected grapes throughout the ripening period and determined their sugar content. Volatile compounds were analyzed using gas chromatography coupled to mass spectrometry (GC-MS).

The researchers found that plants with the fewest grape clusters had the fastest increase in sugar content and were ripe the earliest. The plants that were both thinned out and watered more had the slowest rate of sugar accumulation. The researchers found that slowing down grape ripening decreased the content of, e.g., C₆ aldehydes and alcohols, as well as 2-isobutyl-3-methoxypyrazine (IBMP)—compounds that are associated with “green” and vegetal wine notes. At the same time, slower ripening increased norisoprenoids and terpenes, which are associated with pleasant floral and fruity wine notes. Thus, longer growing time improved the quality of grapes for winemaking. According to the researchers, the work needs to be replicated over several vintages to determine the long-term effects of applying these practices to the same vines.