Sensory and chemical profiles of old vine Chenin Blanc wine: dimensions of a different quality
By Dr Hélène Nieuwoudt, South African Grape and Wine Research Institute (SAGWRI), Stellenbosch University
This research, prepared for the Old Vine Academy, asks whether old vine Chenin Blanc wines differ from younger vine Chenins, and how. It tests the question in two ways: with a trained tasting panel, and with chemical analysis of the aroma compounds in the wines.
The trained panel found significant differences between old-vine and young-vine wines in six of the eight in-mouth attributes reported. The chemical analysis found that old vine and younger vine Chenins contain the same aroma compounds, at different levels of abundance.
Sensory evaluation of old vine Chenin Blanc
The sensory work followed four steps: generating a lexicon to describe the wines, training the panel, evaluating the wines, and visualising the outputs for the industry.
Step 1: Generating the lexicon
The lexicon came from two sources: published sensory notes in Platter's Wine Guide, and a wine masterclass run by an industry expert to align the sensory panel. The Platter's notes describe in-mouth sensations in wines from vines older than 40 years, and are compiled in the word cloud in Figure 1. The most prominent terms are textured, concentration, length, rich, rounded and slippery, along with four descriptors of acidity: crisp, crunchy, dazzling and refreshing.
Figure 1: In-mouth descriptors for wines from vines older than 40 years, from Platter's Wine Guide (R Crous, V Panzeri, J Brand)
Step 2: Training the panel
Panel training used a ballot: a predetermined list of attributes. The panel worked to reach consensus on where reference standards sit on the line scale, and on definitions for each attribute. The definitions came from a compilation of different sources, and the best understood definitions, and the ones that best represent the attribute within this product category, were selected. Reference wines with predetermined line-scale values showed how each attribute is perceived in wine, and were used in both training and testing.
Step 3: Evaluating the wines
The evaluation used descriptive analysis (DA), with consensus training and ballot training for the panel. Six in-mouth attributes were significantly different between old-vine and young-vine wines, and two were not (Table 1).
Table 1: In-mouth attributes compared between old-vine and young-vine wines (R Crous, V Panzeri, J Brand)
Significantly different | Not significantly different |
Body | Heat |
Concentration | Acidity |
Complexity | |
Integration | |
Balance | |
Length |
Figure 2: The sensory panel at work (R Crous, V Panzeri, J Brand)
Step 4: Visualising the outputs
The research team treats visualising the outputs as very important for the industry. Two outputs came from the sensory work: an updated aroma wheel and a technical sheet.
The updated aroma wheel for Chenin Blanc wines (Figure 3) includes old-vine attributes based on this research. They are marked with arrows.
Figure 3: Updated aroma wheel for Chenin Blanc wines. Arrows mark old-vine attributes included based on this research (R Crous, V Panzeri, J Brand, H Botha)
The technical sheet (Figure 4) sets out where old vine Chenin Blanc is planted, a typical taste profile and typical aromas. Typical old vine Chenin aromas shown on the sheet include chamomile, quince jelly, grapefruit, lemon, gooseberry, pineapple, marmalade and white pepper.
Figure 4: Technical sheet on old vine Chenin Blanc wine aroma (R Crous, V Panzeri, J Brand, H Botha)
The sheet lists 1 361.7 ha of old vine Chenin Blanc, counting vineyards of 35 years and older according to the Old Vine Project, out of 17 706.86 ha of Chenin Blanc planted in South Africa (SAWIS, Status of Wine Grape Vines 2016). Table 2 shows the split by region.
Table 2: Regions with old vine Chenin Blanc (35 years and older), as listed on the technical sheet
Region | Old vine Chenin Blanc (ha) |
Stellenbosch | 396.74 |
Paarl | 394.35 |
Swartland | 335.13 |
Olifantsrivier | 95.98 |
Breedekloof | 61.01 |
Robertson | 27.71 |
Worcester | 24.38 |
Klein Karoo | 18.46 |
Northern Cape | 7.94 |
Total | 1 361.7 |
Aroma chemistry: are old vine and younger vine Chenins different?
The chemistry work asked the same question from a different angle. It followed three steps: extracting the aroma compounds from the wine, identifying and quantifying them, and comparing the old vine and younger vine profiles.
Step 1: Extracting the aroma compounds
Three extraction methods were compared: liquid-liquid extraction (LLE), headspace solid phase micro-extraction (HS-SPME) and solid phase extraction (SPE). Table 3 gives the conditions for each, and Figure 5 shows the wine profiles the three methods produced.
Table 3: Sample preparation conditions by extraction method (S Ngxangxa, A Tredoux, A de Villiers)
Method | Wine sample | Solvent, fibre or cartridge | Conditions |
LLE | 5 mL wine | 1 mL dichloromethane (DCM) | 15 min |
HS-SPME | 11% wine/water (v/v) | DVB/CAR/PDMS fibre | 50°C, 30 min extraction time, 30% NaCl salt content |
SPE | 40 mL wine | SDB-L cartridge (500 mg/3 mL) | Rinse: 20 mL 1% NaHCO₃ in 50% MeOH/H₂O. Elution: 1.5 mL DCM |
Figure 5: Wine profiles from the three extraction methods, LLE, SPME and SPE (S Ngxangxa, A Tredoux, A de Villiers)
Step 2: Identifying and quantifying the compounds
About 128 aroma compounds were identified by gas chromatography-mass spectrometry (GC-MS). Figure 6 shows two examples: ethyl butyrate, described as fruity, and isobutyl alcohol, described as wine-like.
Figure 6: Mass spectra of two of the aroma compounds identified by GC-MS (S Ngxangxa, A Tredoux, A de Villiers)
Step 3: Comparing old vine and younger vine profiles
The answer to the research question is yes. The old vine (O) and younger vine (Y) Chenins have different aroma profiles, and in the score plot in Figure 7 the two groups of wines sit apart. The overlay of chromatograms in Figure 8 shows the same compounds in both groups, at different levels of abundance.
Figure 7: Aroma profiles of old vine (O) and younger vine (Y) Chenin Blanc wines (S Ngxangxa, A Tredoux, A de Villiers)
Figure 8: Chromatogram overlay of old vine and younger vine Chenins. Same compounds, different levels of abundance (S Ngxangxa, A Tredoux, A de Villiers)
Acknowledgements
Sensory research: R Crous, V Panzeri, J Brand and H Botha, SAGWRI, Department of Viticulture and Oenology, Stellenbosch University, with C van Zyl (Wine Master) and I Smith (Manager, CBA).
Chemistry research: S Ngxangxa, A Tredoux and A de Villiers, Separation Sciences, Department of Chemistry, Stellenbosch University.
Winetech and the NRF funded the Chenin Blanc research programme. Thanks also to the Chenin Blanc Association, the private Chenin producing cellars, SAGWRI and Stellenbosch University, the post-graduate students and colleagues at Stellenbosch University.