Temperature can play a significant role in the development of wine at many stages during its lifetime. Elevated temperature, however, poses a significant risk to the sensory attributes of wine and its resultant shelf-life. Wines often experience difficult environmental conditions during transport and storage, and this can directly impact on the colour, aroma and mouthfeel of the wine. Higher and/or fluctuating temperature can essentially accelerate the ageing process. Unfortunately, these changes often go unnoticed until the wine reaches the consumer. Numerous studies have investigated the impact of elevated temperature on wines, with noticeable effect, such as reduction of sulfur dioxide, colour development (especially browning of white wines) and changes in the profile of volatile compounds, being common. Unfortunately, most of these studies tend to have a narrow scope and tend to focus only on a limited number of wine types or on specific compounds. The chemistry changes involved in heat-affected red wines are generally more complex than they are in white wines, but it is arguable that white wines are more sensitive to the effect of heat and therefore require the same or a greater level of research consideration with respect to temperature effects. The focus of this review is to highlight the common effects that different wine types and styles can experience when subjected to elevated storage temperature that are considered to be beyond the limits that most winemakers and consumers would accept. This review will also summarise the fundamental chemical kinetics that play a significant role in wine development at elevated temperature.
Cabernet Sauvignon and Shiraz grapes were sourced from different regions within Australia, and microvinified with a skin contact period of 6 days. Grape samples were extracted using two protocols: a 15% v/v ethanol, 10 g/L tartaric acid extract of gently crushed berries (wine-like, WL) and a 50% v/v ethanol, pH 2 extract of grape berry homogenate. It was found that in WL extracts, grape tannin and anthocyanin concentrations were strongly related to wine tannin, anthocyanin and color density achieved during the skin contact period. No relationship was observed for grape tannin concentration analyzed in homogenate extracts and wine tannin, but a strong, positive relationship was found for anthocyanin concentration. When the data obtained from homogenate extraction was treated separately by grape variety, a stronger relationship between grape and wine tannin concentration was observed. Tannin compositional analysis in wines indicated that higher tannin concentrations were due to the extraction of tannin of higher molecular mass during fermentation, most likely from grape skins.
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