A viticultural perspective of Meso-scale atmospheric modelling in the Stellenbosch wine growing area, South Africa

Over the last years, the potential use of non-Saccharomyces yeasts to modulate the production of target metabolites of oenological interest has been well recognized. Among non-Saccharomyces yeasts, Starmerella bacillaris (synonym Candida zemplinina) is considered one of the most promising species to satisfy modern market and consumers preferences due to its peculiar characteristic (enhance glycerol and total acidity contents and reduce ethanol production). Mixed fermentations using Starm. bacillaris and Saccharomyces cerevisiae starter cultures represent a way to modulate metabolites of enological interest, taking advantage of the phenotypic specificities of the former and the ability of the latter to complete the alcoholic fermentation. However, the consumption of nutrients by these species and their produced metabolites may inhibit or stimulate the growth (and malolactic activity) of lactic acid bacteria (LAB).

Valpolicella is a famous wine producing region in the province of Verona owing its fame above all to the production of two Protected Designation of Origins (PDOs) withered wines: Amarone and Recioto. In recent years, however, the wineries have been interested in the enhancement and qualitative increase of another PDO, Valpolicella Superiore. All the Valpolicella PDOs wines are produced with a unique grape blend, mainly Corvina, Corvinone, Rondinella and a range of other minor varieties.From 2019 Valpolicella product regulation has changed the grape proportion of the blend allowing new composition parameters of wines. For this reason, studying the volatile chemical profiles to support wine makers in the effort to produce high quality wines represents a field of great interest.

Climate change constitutes an enormous challenge for humankind and for all human activities, viticulture not being an exception. Long-term strategic changes are probably needed the most, but growers also need to deal with short-term changes: summers that are getting progressively warmer, earlier harvest dates and higher pH in musts and wines. In the last 10-15 years, a relevant corpus of research is being developed worldwide in order to evaluate to which extent extreme canopy management operations, aimed at reducing leaf area and, thus, limiting the source to sink ratio, could be useful to delay ripening. Although extreme canopy management can result in relevant delays in harvest dates, longer term studies, as well as detailed analysis of their implications on carbohydrate reserves, bud fertility and future yield are desirable before these practices can be recommended.

The gustatory balance of wines relies on sweetness, bitterness and sourness. In dry wines, sweetness does not result from the presence of residual sugar as in sweet wines, but is due to other non-volatile compounds. Such taste-active compounds are released during winemaking, by grapes, yeasts or oak wood and belong numerous chemical families [1]. Beyond this diversity, stereochemistry of molecules can also influence their sensory properties [2]. However, the molecular determinants associated with this taste have only been partially elucidated. Astilbin (2R, 3R) was recently reported to contribute to wine sweetness [3]. As its aglycon contains two stereogenic centers, three other stereoisomers may be present: neoisoastilbin (2S, 3R), isoastilbin (2R, 3S), and neoastilbin (2S, 3S). These compounds have already been observed in natural products, but never in wine. This work aimed at assaying their presence for the first time in wines as well as their taste properties.The isomers were synthesized from astilbin and purified by semi-preparative HPLC.

Context and purpose of the study ‐ Crop load management by cluster thinning can improve ripening and the concentration of key metabolites for grape and wine quality. However, little work has been done on testing the impact of crop load management on terpene content of white grapes. The goal of the study was to assess if by reducing crop load via cluster thinning growers can increase terpene concentration of grapes, as well as to test if the timing of thinning application affects terpene concentration.