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Research On Chenin Blanc
by Dr Johann Marais ARC Infruitec-Nietvoorbij, Stellenbosch
In recent years there has been renewed efforts to exploit the full potential of Chenin blanc as a white wine cultivar. In the past, as well as at present, Chenin blanc produces mostly neutral white wines, characterised only by a fermentation bouquet, which is soon replaced by what is usually a uniform bottle aged bouquet. Consequently Chenin blanc wines generally lack complexity and the ability to keep.
Research on Chenin blanc was undertaken at the ARC Infruitec-Nietvoorbij with financial support from Winetech from 2000 to 2005. The purpose of this specific investigation was to determine the effect of viticultural factors such as berry size, ripeness and exposure to sunlight, and oenological factors such as yeast strain, lees contact and period of storage on wine quality and develop procedures that would produce quality wines with the ability to keep longer.
In brief the main drift of the research results may be summarised as follows:
For the viticultural investigation, differences in berry size were achieved by pruning or irrigation. Grapes of the small and large berry treatments (grapes that had been exposed to sunlight and those that ripened in the shade) were harvested at both 21°B and 24°B. Although ester concentrations and wine quality varied between berry size treatments, the pattern was for the small berry treatments to produce higher quality wines. However, both ester levels and wine quality tended to have higher values in the wines made from the riper grapes (24°B). With regard to the comparison between grapes that had been exposed to sunlight and grapes that had ripened in the shade, the latter produced bigger berries almost throughout and the corresponding wines had higher ester levels and higher wine quality. Under the conditions of this investigation, it seems that Chenin blanc grapes should achieve optimal ripeness at between 21°B and 24°B, but possibly closer to the higher degree of ripeness. An attempt should be made to reduce the berry size either through pruning or irrigation, since it appears that the smaller berries produce higher quality wines. Furthermore direct sunlight on grapes should be avoided, because grapes that ripen under indirect sunlight conditions produce higher quality wines.
With regard to the yeast strain and lees contact investigation, four yeast strains, namely VIN 13, N 96, QA 23 and NT 116 were compared. Three treatments, namely the control (no lees contact), standard lees contact and lees contact combined with enzyme treatment, were conducted in combination with the four yeast strains. After five months on the lees, yeast strain QA 23 produced the most fruitiness, lees character and highest overall wine quality. It looks as though yeast strain N 96 produced slightly fuller wines than the other yeast strains. As far as the comparison between the control and the two lees treatments is concerned, the enzyme treatment produced the most lees character, the most body and statistically the highest overall wine quality. Under the conditions of this investigation, yeast strain QA 23 combined with enzyme treatment during lees contact provided the best parameters for the vinification of Chenin blanc wines in which lees character and more body are required.
With regard to the shelf life of Chenin blanc wine, the wines were subjected to different treatments after fermentation and stabilisation. Two pH adjustments of 0.3 units were made, one above and one below the existing pH. Aeration and nitrogen sparging took place with medical air and pure nitrogen respectively. A number of pure phenols (anti-oxidants) and a commercial phenol preparation were added to the wines. Chenin blanc wines from the concurrent viticultural study mentioned above were also used in this investigation. These wines were vinified from grapes picked at different berry sizes (small and large), different degrees of ripeness (21°B and 24°B) and grapes that had been cultivated under shaded conditions as well as exposed to sunlight.
Wines of which the pH had been increased by 0.3 units showed the best ageing potential. Furthermore, wines made from grapes with small berries, and which ripened fully in shady conditions, displayed the best potential for a longer shelf life.
During the shelf life investigation it was found that effective oxygen management after fermentation, up to and during bottling, is absolutely essential. Furthermore it may be stated that for fruitiness to be retained and the formation of bottle aged character to be limited, the storage of white wine at temperatures below 10øC (as proven by previous investigations) remains the most effective practice.
This study therefore concluded that factors such as berry size, sunlight exposure, grape ripeness, yeast strain, lees contact and storage conditions have a prominent effect on Chenin blanc wine style and quality. The results provide guidelines for the production of high quality Chenin blanc wine with a longer shelf life.
More information about aspects discussed in this article may be obtained from the articles mentioned below.
A complete updated literature overview and list regarding Chenin blanc are available from the Sawis industry library.
For more information, address queries to Dr Johann Marais at tel (021) 809-3096 or email maraisj@arc.agric.za.
Literature references
Marais, J., 2003. Literatuuroorsig oor Chenin blanc navorsing. Wynboer 173, 13 - 15.
Marais, J., Van Schalkwyk, D. & October, F., 2005. Effek van korrelgrootte, sonligblootstelling en rypheid op Chenin blanc wynkwaliteit. Wynboer 192, 14 - 15.
Marais, J. & Jolly, N., 2005. Effek van gisras en gismoerkontak op Chenin blanc wynkwaliteit. Wynboer 193, 15 - 17.
Marais, J., 2005. Kan die raklewe van Chenin blanc wyn verleng word? Wynboer 194, 11 - 13.
Summary
Berry size, sunlight exposure, grape ripeness, yeast strain, lees contact, pH, air and nitrogen sparging have a prominent effect on Chenin blanc wine quality and shelf life. Results, obtained under the conditions of this investigation, suggest that yeast strain QA 23 together with enzyme treatment during lees contact, were the best parameters for the production of Chenin blanc wines where lees character and more body are required. The ageing potential of Chenin blanc wine was markedly enhanced by an increase in pH of 0.3 units. Furthermore, it appears that wines produced from grapes with small berries, ripened under shady conditions and harvested at full ripeness showed the best potential to keep longer. Aspects such as oxygen management after fermentation up to bottling are of crucial importance.
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