In this three part series, we explore some fundamental aspects of sulphur and nitrogen foliar fertilisation and the chemical and sensory results of a recent project that took place in South Africa.
Foliar fertilisation and wine aroma
Vine nutrition plays a crucial role in vine development, canopy growth and composition of the grape berry.1,2 Traditionally, vineyard nutrition was carried out by adding fertilisers to the soil to be absorbed by the roots of the plant. Due to climate change and more frequent summer droughts, soil fertilisation is no longer the best solution to increase the nitrogen levels of the must and vines.3-5 Foliar spray fertilisation is a widely-used technique on various crops and can lead to a quick nutrient uptake through the leaves.6-8 Nitrogen foliar fertilisation is only effective in plants approaching nitrogen deficiency and deficiencies can be overcome temporarily.9
Aroma compounds in wine contribute directly to the quality of wine.10 Therefore, an ongoing goal of winemakers is to improve aromatic expression and complexity of wines.11 Some aroma compounds in wines are influenced by the amino acid composition of the initial grape juice. Grape juice with low YAN (amino acids and ammonia) can lead to low yeast populations, poor fermentation vigour and increased risk of sluggish or stuck alcoholic fermentations.12 Various viticultural factors, such as canopy management and nutrition, can influence the juice YAN and therefore the quality and aromatic expression of wines.2,13
Nutrition levels can be adjusted or supplied to the vines through soil fertilisation or by applying foliar fertilisation sprays, meanwhile DAP or complex nutrients can be added in the cellar to grape musts.14 Previous research proved that nitrogen foliar fertilisation can result in increased levels of amino acids in the must.3,13 Therefore, nitrogen with or without sulphur foliar nutrition can enhance the aromatic expression in wines.2,13
It has been shown that foliar fertilisation with nitrogen (N) and nitrogen with sulphur (N+S) at véraison positively impacts the berry chemical composition, yeast growth and metabolism, and produces more aromatic wines. Most foliar research studies have mentioned and have proven positive effects when fertilisation applications were performed prior to and at véraison, due to the vine’s nutrient uptake patterns and requirements.13,15 By doing nitrogen and sulphur foliar applications at véraison, the concentrations of N- and S-containing compounds can be increased. The studies show that N and N+S applications can positively affect various volatile and non-volatile compounds in grapes, musts and resulting wines. Increased levels of N and S compounds, such as YAN, FAN, amino acids and volatile thiols, were measured following the treatments.7,8,13,15-22
Chenin blanc and Sauvignon blanc
In South Africa, Chenin blanc and Sauvignon blanc are two of the most planted white wine cultivars. By means of renewed interest by researchers and the industry, Chenin blanc wines have increased in quality and aroma styles in the past few years. Research by Lawrence (2012)23 on Chenin blanc investigated analytical methods and aroma compounds, such as esters, monoterpenes, higher alcohols and fatty acids. Only recently volatile thiols levels in Chenin blanc have been reported by Wilson (2017).24
Many studies have been performed on Sauvignon blanc with the key focus on aroma compounds that influence aroma expression. A combination of odour-active aroma compounds gives the specific aromatic character of Sauvignon blanc. They are the methoxypyrazines that are found in grapes, and the thiols and major volatiles that are formed from precursors during alcoholic fermentation.3 Most foliar nutrition research has focused widely on thiols.13,19,25
Recent studies with N and S foliar fertilisation applications resulted in Sauvignon blanc juice and wine having higher volatile thiol levels and improved aromatic potential.7,13,25 Increased glutathione (GSH) levels were obtained where soil nitrogen, as well as foliar nitrogen and sulphur foliar applications, were done.13 Due to its antioxidant properties, GSH plays an important role in Sauvignon blanc wines by protecting the aroma compounds, such as volatile thiols.26
The various foliar fertilisation studies have been performed on Sauvignon blanc in different locations in the world (usually cool climate areas) and varied in application products, rates and times. Chenin blanc is one of South Africa’s most important and planted white cultivars, and to date no foliar fertilisation trials have included this cultivar. Only two soil fertilisation studies have been done on Chenin blanc,27,28 both of them in South Africa.
In general since few research studies regarding foliar fertilisation have been published and most trials have been conducted under European conditions on various white and red wine cultivars,7,8,13,29-33 it was of interest to us and the industry to perform N and N+S foliar applications at véraison on Chenin blanc and Sauvignon blanc in South Africa. Such research was therefore required to compare the outcome to previous trials (Sauvignon blanc) to evaluate foliar fertilisation in local context (Chenin blanc and Sauvignon blanc) and to contribute to the knowledge regarding Chenin blanc as a whole.
South African project aims and objectives
The limitations of the previous foliar fertilisation studies are linked to both chemical and sensory aspects. Methoxypyrazines and major volatiles are important aroma compounds and have not been analysed in foliar fertilisation research studies. Only a few research studies determined the vine nitrogen status before and after foliar applications.7,13,22 Only two studies have done sensory analysis of the finished wines, but do not mention the age of the wines.13,19 Another gap in foliar fertilisation research studies is that chemical and sensory evolution of wines during bottle maturation have not been considered.
To this end, a project was proposed to study the effect of N and S foliar fertilisation treatments on the chemical composition of the juice and wine of V. vinifera L. cultivars Chenin blanc and Sauvignon blanc. This was accomplished by evaluating the treatment effects on non-volatile content (amino acids, GSH and YAN) at various stages of winemaking and on volatile composition (major volatiles, methoxypyrazines and volatile thiols) in wine. Furthermore, the effect on the aroma composition of the wines was evaluated sensorially. These aspects constitute the topic of the next two articles in the series.
Positive results of foliar fertilisation studies in vineyards have gained the attention of South Africa’s wine industry and winemakers who want to positively influence the aroma and complexity of wines through this viticultural practice.
The complexity of the various chemical compounds present in the grape berry and must can contribute to the intricate aromatic expression, flavour and mouth-feel properties of a wine. Many winemakers and viticulturists have experimented with various processes in the cellar or practices in the vineyard to positively influence the non-volatile and volatile compounds present in grapes and wine. Vine nitrogen fertilisation has been shown to have a positive impact on the composition of grapes. Due to climate change and frequent summer droughts, foliar fertilisation has been widely used on various crops and can lead to a quick nutrient uptake through the leaves.
- Bell SJ, Henschke PA. Implications of nitrogen nutrition for grapes, fermentation and wine. Aust J Grape Wine Res. 2005;11(3):242-295. Doi:10.1111/j.1755-0238.2005.tb00028.x.
- Chone X, Lavigne-Cruege V, Tominaga T, et al. Effect of wine nitrogen status on grape aromatic potential: Flavor precursors (S-cysteine conjugates), gluthathione and phenolic content in *Vitis vinifera* L. cv. Sauvignon blanc. J Int des Sci la Vigne du Vin. 2006:1-6. Doi:10.1006/anbo.2000.1361.
- Fischer U. Flavours and fragrances. In: Flavours and Fragrances : Chemistry, Bioprocessing and Sustainability. Berlin, Heidelberg, New York: Springer. 241-67; 2007. Doi:10.1016/S0924-2244(97)01044-3.
- Laget F, Tondut J-L, Deloire A, Kelley MT. Climate trends in a specific Mediterranean viticultural area between 1950 and 2006: Climate and viticulture in the South of France. J Int des Sci la Vigne du Vin. 2008;42(3):113-123. http://knol.google.com/k/alain-deloire/climate-trends-in-a-specific/2rmh6zvf1o8hc/12.
- Keller M. Water Relations and Nutrient Uptake. In: The Science of Grapevines: Anatomy and Physiology. 1st ed. Elsevier Inc.; 2010:85-105. Doi:10.1016/B978-0-12-374881-2.00003-9.
- Christensen LP, Smart DR. Foliar fertilization in vine mineral nutrient management programs. In: Soil Environment and Vine Mineral Nutrition Symposium. 2005:83-90.
- Jreij R, Kelly MT, Deloire A., Brenon E, Blaise A. Combined effects of soil-applied and foliar-applied Nitrogen on the N composition and distribution in water stressed Vitis vinifera L. cv. Sauv. blanc grapes. J Int Sci Vigne Vin. 2009;43(4):179-187.
- Lasa B, Menendez S, Sagastizabal K, et al. Foliar application of urea to “Sauvignon blanc” and “Merlot” vines: Doses and time of application. Plant Growth Regul. 2012;67(1):73-81. Doi:10.1007/s10725-012-9667-5.
- Delas J. Fertilisation de La Vignee. 2nd ed. (Féret, ed.). Bordeaux; 2000.
- Marais J. Sauvignon blanc cultivar aroma: A review. South African J Enol Vitic. 1994;15(2):41-45.
- Loubser F. Chenin blanc table wine in South Africa. Cape Wine Master Diss March. 2008;(March). http://capewineacademy.co.za/dissertations/Cheninblanc_Table_Wines.pdf.
- Monteiro FF, Bisson LF. Biological Assay of Nitrogen Content of Grape juice and prediction of sluggish fermentations. Am J Enol Vitic. 1991;42(1):47-57.
- Lacroux F, Tregoat O, Van Leeuwen C, et al. Effect of foliar nitrogen and sulphur application on aromatic expression of Vitis vinifera L. cv. Sauvignon blanc. J Int Sci Vigne Vin. 2008;42(September):1-8. Doi:10.1007/s11032-013-9938-5.
- Lorenzini F, Vuichard F. Ajout d’acides aminés aux moûts et qualité des vins. Rev suisse Vitic Arboric Hortic. 2012;44(2):96-103.
- Dufourcq T, Charrier F, Poupault P, Schneider R, Gontier L, Serrano E. Foliar Spraying of Nitrogen and Sulfur At Veraison: a Viticultural Technique To Improve Aromatic Composition of White and Rosés Wines. In: 16th International GiESCO Symposium. Viticulture & Enology, UC Davis: Davis, CA, USA. 379-83; 2009.
- Kelly M, Gill Giese W, Velasco-Cruz C, et al. Effect of foliar nitrogen and sulfur on petit manseng (Vitis vinifera L.) grape composition. J Wine Res. 2017;28(3):165-180. Doi:10.1080/09571264.2017.1324774.
- Mundy DC, Hill GN, Beresford RM. Factors effecting susceptibility of Sauvignon blanc grape berries to Botrytis cinerea infection. In: Romeo Bragato Conference. 2009.
- Hannam KD, Neilsen GH, Neilsen D, Rabie WS, Midwood AJ, Millard P. Late-season foliar urea applications can increase Berry Yeast-Assimilable nitrogen in Wine grapes (Vitis vinifera L.). Am J Enol Vitic. 2014;65(1):89-95. Doi:10.5344/ajev.2013.13092.
- Geffroy O, Charrier F, Poupault P, et al. Foliar Nitrogen and Sulfur Spraying Allow To Produce Wines With Enhanced Concentration in Varietal Thiols. Macrowine from June 27 – 30, 2016. 2016;(June):81310.
- Koestel C, Dienes-Nagy Á, Fuchsmann P, et al. Impact of different nitrogen levels in the vineyard and wine-making processes on the chemical profile of Chasselas wines. In: International Conference WAC 2017. Beaune, France; 2017.
- Gutiérrez-Gamboa G, Garde-Cerdán T, Gonzalo-Diago A, Moreno-simunovic Y, Martinez-Gil A. Effect of different foliar nitrogen applications on the must amino acids and glutathione composition in Cabernet Sauvignon vineyard. Elsevier. 2017;75:147-154. Doi:10.1016/j.lwt.2016.08.039.
- Helwi P, Guillaumie S, Darriet P, Van Leeuwen C, Thibon C. The impact of vine Nitrogen status on aroma potential expression in Vitis vinifera L. cv. Sauvignon blanc [Internet]. Available from:http://congresdesterroirs.org/articles/lire/248. Int Terroir Congr. 2014.
- Lawrence N. Volatile metabolic profiling of SA Chenin blanc fresh and fruity and rich and ripe wine styles : Development of analytical methods for flavour compounds (aroma and flavour) and application of chemometrics for resolution of complex analytical measurement. MSc Thesis Inst Wine Biotechnol. 2012;(March).
- Wilson CL. Chemical evaluation and sensory relevance of thiols in South African Chenin blanc wines. 2017.
- Dufourcq T, Charrier F, Poupault P, Schneider R, Gontier L, Serrano E. Foliar spraying of Nitrogen and Sulfur at veraison: A viticultural technique to improve aromatic composition of white and roses wines. In: 16th International GiESCO Symposium, Davis (USA). Davis, USA; 2007:379-383.
- Dubourdieu D, Lavigne V. The role of glutathione on the aromatic evolution of dry white wine. Vinidea.net Wine Internet Tech J. 2004;02(2):1-9.
- Conradie WJ. Nutrient Consumption by Chenin blanc grown in Sand Culture and Seasonal Changes in the Chemical Composition of Leaf Blades and Petioles. South African J Enol Vitic. 1981;2(1):15-18.
- Conradie WJ, Saayman D. Effects of Long-Term Nitrogen, Phosphorus, and Potassium Fertilization on Chenin blanc Vines. II. Leaf Analyses and Grape Composition. Am J Enol Vitic. 1989;40(2):91-98.
- Dufourcq T, Nardi S, Geffroy O, Serrano E, Lopez R, Cacho J. Influence de l’itinéraire de Vinification Sur Le Potentiel Aromatique Des Vins de Gros Manseng Des Vins. French Institute of Vine and Wine. France; 2007.
- Verdenal T, Spangenberg JE, Zufferey V, et al. Leaf-to-fruit ratio affects the impact of foliar-applied nitrogen on N accumulation in the grape must. J Int des Sci la Vigne du Vin. 2016;50(1):23-33. Doi:10.20870/oeno-one.2016.50.1.55.
- Garde-Cerdan T, Gutierrez-Gamboa G, Gonzalo-Diago A, Moreno-Simunovic Y, Martinez-Gil A. Effect of different foliar N applications on must AA and GSH Cab Sauvignon.
- Geffroy O, Lopez R, Charrier F, et al. Boosting varietal thiols in white and rosé wines through foliar nitrogen and sulfur spraying. 16th Aust Wine Ind Tech Conf. 2016;(July 2016):102-105.
- Verdenal T, Spangenberg JE, Zufferey V, Lorenzini F, Spring JL, Viret O. Effect of fertilisation timing on the partitioning of foliar-applied nitrogen in Vitis vinifera cv. Chasselas: A 15N labelling approach. Aust J Grape Wine Res. 2015:110-117. Doi:10.1111/ajgw.12116.
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