Browsing by Author "Terblanche, Etienne Louis Adriaan"
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- ItemThe impact of grape ripeness level on berry and wine composition and potential wine style of Vitis vinifera L cv. Pinotage(Stellenbosch : Stellenbosch University, 2019-04) Terblanche, Etienne Louis Adriaan; Hunter, Jakobus Johannes; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.ENGLISH ABSTRACT: The understanding of grapevine reaction to its environment and resulting grape composition, wine composition and sensory profile forms the foundation from which wine producers make product-based/market-related, downstream cultivation decisions. Yet, surprisingly limited information is available to producers with regards to the expected changes in wine style linked to a range of harvest dates, including early or late/delayed harvest. Therefore the main objective of this descriptive study was to create a reference base to better assist practical harvest decision making. The native South African Vitis vinifera L. cv. Pinotage was studied due to its early and rapid sugar accumulation, analogous to the predicted grapevine response due to climate warming. In this field study, the extent of grape- and wine composition and sensory profile changes for cv. Pinotage was assessed at five (R1-R5) ripeness levels that were defined by sugar level/Brix (ca. 21, 23, 25, 27 & 29 °B) over three vintages (2015-17) and two sites planted to Pinotage/140 Ruggeri (A) and Pinotage/1103 Paulsen (B), under Mediterranean conditions (unirrigated), Western Cape, South Africa. The unirrigated grapevines grafted to drought resistant rootstocks adapted well (at physiological level) to low seasonal rainfall and high mean temperatures. Despite canopy deterioration/senescence during late ripening, the spectrum of ripeness levels (R1-R5) was completed within 21 days. Berry sizes remained constant from R1-R4 and accumulation or decrease of berry constituents was considered independent of the concentration effect by berry size reduction (increased skin:pulp ratio) as this only manifested at R5. Late season berry size reduction (dehydration) at R5 was linked to increases in primary metabolites (sugars and acids) and minerals (both phloem and xylem bound), but decreases in phenolic and anthocyanin contents. Concentration of berry phenolic compounds and anthocyanins increased form R1 to R4 (peak), before declining towards R5. Changes in grape aromatic profile were subtle and reaction of key components was significantly influenced by Vintage and Site. Results suggest a relatively minor shift in overall grape aroma profile per ripeness level during the compact harvest window (21 days). Even so, wine volatile profiles displayed significant definition regarding ripeness levels, showing distinctive changes for components of various volatile groups. Importantly, known impact odorants of Pinotage, such as ethyl octanoate (sweet fruit/floral), isoamyl acetate (banana), and β-damascenone (prune), displayed ripeness level related changes. As such, these shifts in aroma profile were also displayed by descriptors and intensities thereof in sensory analyses. Moreover, particularly taste/palate descriptors, including acidity, body, astringency, alcohol and concentration, which were well associated with basic fruit chemistry (sugar, titratable acidity and pH), displayed a controlling effect on sensory profile. This exhaustive grape compositional field study placed ripening related changes in context to those determined/affected by the environment (Vintage/Climate) and Site (Soil & Genotype). It points to the negative effects of extended hang time and provides much needed insight into wine compositional changes during rapid sugar accumulation. Novel sensory information regarding potential wine styles, as differentiated by ripeness level, was generated. This can easily be utilised by producers to achieve the desired product outcome.