Introduction

Winemakers put a lot of effort into producing good quality wine. It is therefore critically important that the wine reaches the consumer in an unaltered state. It is well known that high storage temperatures may adversely affect the quality of wine. This is due to the breakdown of favourable aroma compounds, such as certain esters and thiols for instance. There is also a belief that a variation in temperatures that wines are stored at may also adversely affect its quality.

The shipping of wine and how this affects the sensory composition of wine has not received sufficient attention in the past. A few studies have shown that keeping wine at higher temperatures leads to the development of unwanted colour in white wines, with a loss in the fruity aroma (Hopfer et al., 2012).

Some research has shown that wine can be exposed to very high temperatures, as well as large temperature variations when stored or transported in containers in the harbour or when shipped (Meyer, 2002; Rodriguez-Bermejo et al., 2007). Meyer (2002) found the largest temperature variations that wines are exposed to when shipping containers are stored in the harbour, with that on the sea being relatively constant. This main aim of this work was to investigate the effect of different temperatures to which wine might be exposed to on the sensory composition of white South African wines.

Materials and methods

Two white wines were used in this study, which included a commercial 2009 Sauvignon blanc (closed with a cork), as well as a 2010 Chenin blanc (sealed with a screw cap). The 2010 wine was collected soon after bottling, while the 2009 has been bottled for roughly a year. These wines were then exposed to different temperature changes for 46 days, which were supposed to simulate temperatures when shipped from Cape Town (in summer) to Europe. Part of the wines were thus exposed to 30’C for eight hours, then to 37’C for eight hours and finally to 20’C for the final eight hours per day for one week. This was supposed to simulate one week that the wine would have spent on the Cape Town harbour in a container in summer time. The wines were then moved to a constant 15’C for 30 days (simulating time spend on sea). After this the wines were exposed to simulated European winter conditions for one week, which included storing them at -4’C, 4’C and 8’C for eight hours per day.

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TABLE 1. Mean sensory scores (out of 100) for Chenin blanc after the 46 days temperature trial. Different letters indicate indicates significance at p<0.05

The rest of the wines were left for 46 days at a constant -4′, 15′ and 37’C. The average temperature of the 15’C and variable temperature treatments were very similar over the 46 day trial period.

The wines were then sensorially evaluated by a trained sensory panel of eight judges using descriptive analyses. This sensory method makes use of a line scale where panellists have to indicate the intensity of a certain aroma or taste that they have been calibrated for. The panel consisted of post graduate students and staff of the Department of Viticulture and Oenology, Stellenbosch University. All tasting were conducted in a blind manner and in a random order. After this first trail with four treatments, we also exposed additional bottles of the 2010 Chenin blanc wine to 37’C and 15’C for 7 and 14 weeks for a triangle tasting. For more detail Du Toit and Piquet (2014) can be consulted.

Results and discussion

In Table 1 the sensory results of the Chenin blanc wine can be seen. It is clear that those wines left at a constant 37’C had much higher levels of yellow colour, sulphur off odour, over-aged aroma and a burning aftertaste, which are all negative characteristics often used to describe white wines that was left for too long at high temperatures. These wines were also rated significantly lower in terms of positive aroma characteristics, such as tropical and fruity aromas. However, no significant differences could be observed between the -4’C, variable and 15’C treatments. Similar results were obtained with the Sauvignon blanc wines, but some of the positive fruity aroma compounds were slightly lower in the variable and 15’C treatments compared with that the -4’C treatment. However, these differences were, although significant, still small (around 3% decreases), while the wines left at 37’C had much larger decreases in fruity aromas and high increases in negative associated sensorial characteristics as found in the Chenin blanc wine. It thus seems that temperature variations does not seem to play such a large role in white wines matured in the bottle, but rather the average temperature it is exposed to. A white wine thus stored at say 2 – 12’C (which is a temperature variation of 10’C), will thus age much slower than the same wine left at say 20 – 22’C (which is a temperature variation of only 2’C). These simulated shipping temperatures also did not affect the sensory characteristics of the wines to such a large extent, but high temperatures of up to 50’C during summer has been recorded in some shipping containers.

As the tasters could clearly distinguish the 37’C treatments from the rest after 46 days, we were interested to assess whether they could perceive it at an earlier stage. The Chenin blanc wine was thus also stored at a constant 15’C and 37’C and assessed after one and two weeks. After one week a triangular tasting showed that the panel could not distinguish between these two treatments, but after two weeks they could, indicating that after such a short period of time the wine already underwent a drastic change at such a high temperature.

High temperatures are known to increase acid hydrolysis of certain fruity esters, as well as the hydrolysis of 3-mercaptohexanonacetate, which is responsible for the passion fruit and guava aromas in Sauvignon and Chenin blanc wines (Coetzee et al., 2012). These breakdown reactions do not need oxygen and can thus proceed even if the wines are closed under screw cap, which should be kept in mind by the producer when shipping or storing wines.

Acknowledgments

The author would like to thank Winetech and THRIP for financial support of this work.

Literature cited

Coetzee, C. & Du Toit, W.J., 2012. A comprehensive review on Sauvignon blanc aroma with a focus on certain positive volatile thiols. Food Res. Int. 45, 287 – 298.

Du Toit, W.J. & Piquet, C., 2014. Research note: Effect of simulated shipping temperatures on the sensory composition of South African Chenin and Sauvignon blanc wines. S. Afr. J. Enol. Vitic.

Hopfer, H., Ebeler, S.E. & Heymann, H., 2012. The combined effects of storage temperature and packaging type on the sensory and chemical properties of Chardonnay. J. Agric. Food Chem. 60, 10743 – 10754.

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