WINETECH Technical Yearbook 2019

Transition zone: 140 mg N/L SA Chenin Blanc: 77-288 mg N/L SA Sauvignon Blanc: 78-438 mg N/L

findings are supported by the literature (Lacroux et al ., 2008; Hannam, et al ., 2014; Dienes-Nagy et al ., 2017). YAN was measured in racked juice before inoculation. The statistical analysis shows that even though all the treatments containing N resulted in an increased level of YAN, differences were not significant (Figure 3). However, in cases where YAN was low, the increase as a response to foliar fertilisation with N could make the difference between sub-optimal and acceptable levels. Even when the same vineyard was used for two consecutive seasons (SB 2015 and 2016) the effect of the treatments was the same. Moreover, the total amino acids and arginine (ARG) content in the juices were higher with the N treatments compared to the control, in agreement with previous research (Lasa et al. , 2012). The increase in amino acids is relevant not only for yeast metabolism, but also for the aromatic potential of a wine, as certain amino acids are precursors of aroma compounds. GLUTATHIONE The results and trends of GSH were not as evident as for YAN, though N and N+S treatments generally resulted in higher GSH levels compared to the control for both cultivars and all years (Figure 4) in accordance with previous results from literature (Lacroux et al ., 2008). If the wines have the potential to be aromatic, GSH levels present can play a crucial role by protecting

varietal volatile thiols from oxidation, and therefore protect the aroma expression of wines (Lavigne et al ., 2007). To gain more knowledge on the mechanisms of the foliar fertilisation, various other vineyard measurements can be considered: • Vine measurements, such as light intensity and nitrogen content in the leaves and berries, should be included to determine the canopy density and nitrogen content between the sprays. • Methoxypyraz ines throughout the ripening and winemaking process to see how the levels are affected by the fertilisation sprays. • S u l p h u r - c o n t a i n i n g p r e c u r s o r s , glutathionylated and cysteinylated thiol precursors to be related back to the S foliar fertilisations treatments. TAKE-HOME MESSAGE In this particular study, the foliar treatments did in general not have major effects on YAN and glutathione content. It is only in the lower YAN treatments where foliar application lead to a “significant for practical winemaking” increase in YAN. The industry is encouraged to do their own trials to see where foliar application can work for them and where not. A good place to start would be lower YAN vineyards, keeping in mind that factors influencing the success of foliar fertilisation can be the location

140 mg N/L

Chenin Blanc (2015)

Chenin Blanc (2016)

Sauvignon Blanc (2015)

Sauvignon Blanc (2016)

*significant ↑/↓ ↑ FIGURE 3. ANOVA (Analysis of Variance) for YAN values for the three vintages and the two cultivars studied. Letters indicate significant differences.

of the vineyards (different South African wine regions have different climates), vine age, the cultivar (nitrogen deficient red and volatile-rich cultivars, such as Sémillon, Colombard, Riesling, Cabernet Sauvignon and Merlot) and the combination of soil and foliar fertilisation in the South African climate. The effects of the treatments on the aroma composition and sensory expression of the wines after bottle maturation was also assessed during this project. It will be discussed in Part 3 of the series. SUMMARY The overall aim of this research study

was to investigate the effect of different foliar fertilisation treatments on the chemical composition (volatile and non- volatile compounds) of the juice and wine of Sauvignon blanc and Chenin blanc. Many research studies have been done on the biochemical and chemical origins of non-volatile and aroma compounds and the effects of the environment, and viticultural and winemaking practices on the concentrations on these compounds. By performing chemical and sensory analysis to understand the influence of the effect of N and N+S foliar fertilisation on Chenin blanc and Sauvignon blanc, South African winemakers and the industry can use this information to make decisions at