The aim of this study was to evaluate the stability of commercial white wines aroma using both analytical chemistry and sensory evaluation approaches, with a focus on the stability of thiols. Part 2 is focused on the evolution of the sensory perception of the aroma of the wines during storage.
The sensory evaluation of the wines after storage was done using Pivot©Profile,1 a method that employs a reference (in this case, the control, T0) and compares the rest of the samples in the set to it, while generating a series of attributes for both the reference and the samples. Unwooded Chenin blanc (CB) and Sauvignon blanc (SB) wines were sourced from six wineries. The wines were stored at room temperature (RT), 15°C and 25°C for three and nine months (T3 and T9), after which they were transferred into a -4°C cooling room until analysis. The control for each winery (T0) was stored at -4°C until analysis. Therefore, each sample set consisted of seven samples (T0, T3/15, T3/25, T3/RT, T9/15, T9/25 and T9/RT) per winery for each cultivar, 12 sets in total. The data analysis began with the capture of 180 forms for each SB and CB. A total of 240 attributes were generated with little redundancies. Semantic grouping led to 170 attributes from which frequency of citations were calculated for CB and SB separately. Further condensation based on how many judges used a certain descriptor resulted in 29 attributes for CB and 33 for SB.
The results from the Pivot©Profile allowed us to map the changes with storage time and conditions for each set.
We have evaluated the changes from two perspectives:
- How the wines have changed during storage (which attributes disappeared/appeared) and
- how much the wines changed.
Heat maps are a very useful tool for visualising the sample sets as they are descriptive and intuitive. Read horizontally, a sample is described comparative to the control (Figure 1 and 2) – for each attribute, the intensity can be higher, lower, or the same as for the control. Read vertically, we can see how each attribute was different for a certain sample compared to the control. The dendrogram (on the left side), shows how the samples are related to each other and grouped based on distances (similarities). Further statistical analysis showed that all control samples (T0) were very different from treatments. Treatments were closely associated according to storage time (3 and 9 months).
The experienced panel of judges in this study were consistently able to pick up aroma differences in the treated samples from the control. Changes were observed in attributes/profile, but did not negatively affect the wine aroma for the time period tested (Figure 3).
The control samples were described mostly with ‘fruity’ and ‘floral’ attributes, different from the T3 samples (described mostly with green attributes) and the T9 samples (‘toasted’, ‘oaky’ and ‘woody’). The attributes used for samples stored at lower temperatures for shorter periods of time were more similar to attributes used to describe the control and were different from attributes used for samples stored at higher temperatures for prolonged periods of time (Figure 1 and 2). The evolution of ‘floral’ and ‘fruity’ notes in the controls was more subtle (variation less extreme) in SB than in CB wines. CB control wines, for most of the sample sets, showed a sharper decline in floral and fresh notes over time and at increased temperatures. SB control wines were more ‘fruity’, ‘floral’ and ‘tropical’ than wines stored at higher temperatures for longer, which were more ‘toasty’, ‘oaky’ and ‘spicy’. This is similar to the results on New Zealand SB2 and on Spanish white cultivars3. Both the New Zealand and Spanish study found significant increases in buttery, ripe and spicy attributes and decreases in fruity, fresh and floral attributes with higher storage temperatures. In our study, only one winery’s SB sample set was an exception as the control had particularly higher ‘pineapple’, ‘green’ and less ‘fruity’ notes compared to the other wineries. ‘Fresh’ remained relatively unchanged, with only some wineries’ sample sets showing a slight decrease with higher temperature and longer storage times.
FIGURE 1. Heat map of a CB sample set indicating the attributes that have changed with storage, how much they changed (higher or lower), and how the samples are similar based on these attribute changes.
FIGURE 2. Heat map of a SB sample set indicating the attributes that have changed with storage, how much they changed (higher or lower), and how the samples are similar based on these attribute changes.
Most interestingly, further statistical analysis made it possible to demonstrate that for each cultivar and regardless of the initial wine sensory profiles, the storage conditions had similar effects on the evolution of the wines (with one exception). In other words, even if the wines were described differently, they changed in a similar pattern.
FIGURE 3. General changes in the aroma attributes with storage.
The exception can possibly be explained by the fact that the thiol and colour parameters for that sample set were also different from the other wineries. In other words, the chemical composition of these wines influenced 1) how the wines were perceived and 2) how the wines changed during storage.
Take home message
This is the first time that a parallel study was done on Sauvignon blanc and Chenin blanc wine storage effects. The results showed that time played the most important role during storage, regardless of the storage temperature. The study demonstrated the applicability of the rapid sensory method (Pivot©Profile) for this type of experiments (comparison to an initial/reference stage/sample). Moreover, this method was never before used in the evaluation of time-related experiments.
Statistical analysis showed that all control (T0) wines were very different from the wines after storage, regardless of the initial wine profile. Similar to the chemistry results presented in Part 1, the sensory evolution of the wines was not generally affected by the initial wine profile for all six Sauvignon blanc and six Chenin blanc wine sets included in the project. In other words, in almost all cases the changes observed were similar, regardless of how the time 0 wine was perceived. Based on the sensory results, wines stored at higher temperatures for longer were perceived as more ‘toasty’, ‘woody’, ‘oak’ and ‘honey’, while those stored at lower temperature for shorter period were perceived as ‘floral’ and ‘tropical’ in comparison to the initial wine.
Wine aroma is susceptible to change during storage, especially at high temperatures. In a recent study at the Department of Viticulture and Oenology of Stellenbosch University, we investigated changes in South African Sauvignon blanc and Chenin blanc wine sensory profile, volatile composition and antioxidant-related parameters resulting from storage of unwooded wines under different temperatures (room temperature, 15°C and 25°C) and durations (0, 3 and 9 months). Statistical data analysis was used to assess the correlations in the sensory and chemical evolution of the wines relative to the control (time 0).
- Thuillier, B., Valentin, D., Marchal, R. & Dacremont, C., 2015. Pivot©Profile: A new descriptive method based on free description. Food Quality and Preference 42: 66 – 77. DOI: 10.1016/j.foodqual.2015.01.012.
- Makhotkina, O., Pineau, B. & Kilmartin, P.A., 2012. Effect of storage temperature on the chemical composition and sensory profile of Sauvignon blanc wines. Australian Journal of Grape and Wine Research 18(1): 91 – 99. DOI: 10.1111/j.1755-0238.2011.00175.x.
- Pérez-Coello, M.S., González-Viñas, M.A., Garcia-Romero, E., Diaz-Maroto, M.C. & Cabezudo, M.D., 2003. Influence of storage temperature on the volatile compounds of young white wines. Food Control 14(5): 301 – 306. DOI: 10.1016/S0956-7135(02)00094-4.
– For more information, contact Astrid Buica at firstname.lastname@example.org.