WW ASB 14-01
Effects of nitrogen foliar fertilization on berry composition and wine aroma (cv Cabernet Sauvignon and Sauvignon blanc, Vitis vinifera L.)
Stellenbosch University. Department of Viticulture and Oenology
Du Toit, W J
There is a demand for wine styles that suit the market preferences. The ability of the winemaker to manipulate wine to meet this demand results in higher income for the various cellars in particular and for the industry in general. During winemaking there are a number of means by which the winemaker can adjust the style of the wine for example, the choice of yeast to elicit certain aroma characteristics. The grape produces wine’s final aroma.
In Sauvignon blanc, the two main classes of varietal aroma compounds are thiols and methoxypyrazines. Thiols are associated with the tropical style of Sauvignon blanc, while methoxypyrazines impart green, grassy characteristics. Being able to express preferentially one of these classes of compounds results in the wine style associated with the respective class. If vineyard treatments can influence the production of one type of compounds over the other, the issue of wine style is already partly solved. Appropriate winemaking practices has to be used in order to preserve the respective wine style. During fermentation esters and higher alcohols are produced, which also contribute to the aroma profile of the wine.
Nitrogen content of must plays an important role in the fermentation rate and amino acids are precursors of volatile compounds of wine, such as esters. The role of amino acids as wine aroma precursors can explain the positive correlation between healthy nitrogen levels in must and sensory assessments. Controlling nitrogen levels in grape and must is essential for the production of quality wine. Generally, nitrogen additions in the cellar seek to correct the levels of nitrogen available for yeast, but a good control of these levels should start in the vineyard, mainly in relation with the biosynthesis of berry aromatic precursors.
The focus of this study is the evaluation of nitrogen and sulphur foliar applications at different phonological stages on two cultivars, Sauvignon blanc and Chenin blanc. Practically, the aims are: to identify threshold values of nitrogen and sulphur foliar fertilization required to optimize the fermentation of musts; to enhance the expression of certain varietal aroma compounds (thiols vs methoxypyrazines) and aromatic precursors in the berry (i.e. amino acids); and to influence the wine aromatic profile by manipulation of FF treatments.
In other words: to assess the quality and quantity of thiols as affected by foliar fertilization by sulphur; to assess the quality and quantity of amino acids (as berry aroma precursors) as affected by foliar fertilization with nitrogen; and whether this type of fertilization has a positive impact on the aroma of the wine. Another outcome of the project is to see the influence of the nitrogen foliar fertilization on the quantity of methoxypyrazines present in the grapes (and therefore the impact on the final wine) data for this possible correlation is not available at his time.
Buica, A, Bruwer, FA, du Toit, W. 2016. The effect of nitrogen and sulphur foliar applications in hot climates. Presented at MacroWine 2016. 27-30 June, Changins, Switzerland.
Bruwer, FA, du Toit, W J, Buica, A. 2016. Effect of nitrogen and sulphur foliar fertilization on non-volatile compounds of Vitis Vinifera L. Chenin blanc and Sauvignon blanc cultivars. Poster presented at the South African Society of Enology Viticulture Conference. 23-25 August, Somerset West, South Africa.
Bruwer, F A, Du Toit, W J, Buica, A. 2016. Effect of nitrogen and sulphur foliar fertilization on wine volatile compounds of Vitis Vinifera L. Chenin blanc and Sauvignon blanc cultivars. Poster presented at the South African Society of Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.
Bruwer, F A, Du Toit, W J, Buica, A. 2016. The evolution of wine volatile composition during wine storage. Poster presented at In Vino Analytica Scientia Symposium. 18-20 July, Salamanca, Spain.
Bruwer, A, du Toit, W, Buica, A. 2016. The effect of nitrogen and sulphur foliar fertilization on sensory aspects of Chenin Blanc and Sauvignon Blanc wines, Focus on Chenin Blanc,