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The impact of grape berry ripeness level on berry and wine composition and potential wine style of Vitis vinifera L cv. Pinotage

by | Oct 28, 2020 | Viticulture

Project Number: WW ET 15-01

Project title: The impact of grape berry ripeness level on berry and wine composition and potential wine style of Vitis vinifera L cv. Pinotage

Project leader: Terblanche, E

Team members
Terblanche, E
Hunter, J J
Strever, A E
Volschenk, N

Project completed: 2019


Objectives and rationale: Understanding grapevine reaction to its environment and resulting grape – and wine composition and sensory profile forms the foundation for wine producers to make product-related, downstream cultivation decisions. Yet, surprisingly limited information is available to producers regarding the expected changes in wine style linked to a range (early to late/delayed) of harvest dates. Therefore, the main objective of this descriptive study was to create a reference base to assist in practical harvest decision-making. Pinotage was studied due to its early and rapid sugar accumulation, analogous to the predicted grapevine response due to climate warming.

Methods: In this field study, the extent of grape- and wine composition (chemical, phenolic and volatile components) and sensory profile changes were 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 dryland cultivation at Welgevallen Experimental Farm, Stellenbosch University.

 Key results:

  • The unirrigated grapevines grafted to drought-resistant rootstocks adapted well (at the physiological level) to low seasonal rainfall and high mean temperatures.
  • Despite canopy deterioration during late ripening, the spectrum of ripeness levels (R1-R5) was completed within 21 days.
  • Berry sizes remained constant from R1-R4, and the accumulation or decrease of berry constituents was considered independent of the concentration effect by berry size reduction, which only manifested at R5.
  • Late-season berry size reduction (dehydration) at R5 was linked to increases in sugars, acids, and minerals (both phloem and xylem bound) but decreases in phenolic and anthocyanin contents.
  • The concentration of berry phenolic compounds and anthocyanins increased from R1 to R4 (peak) before declining towards R5.
  • Changes in grape aromatic profile were subtle, and vintage and site significantly influenced the reaction of key components.
  • Results suggest a relatively minor shift in the overall grape aroma profile per ripeness level during the compact harvest window (21 days). Even so, wine volatile profiles displayed significant definitions 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/tobacco), 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 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.

Conclusions: This exhaustive grape compositional field study placed ripening-related changes in context with those determined by the environment (vintage/climate) and site (soil and genotype). It points to the negative effects of extended hang time and provides much-needed insight into wine compositional changes during rapid sugar accumulation.

Recommendation to industry / Key take-home message: Novel information was created regarding wine stylistic changes along a ripeness gradient. Producers may use this to guide harvest decisions and identify maturity points of interest to their specific portfolio needs.

Etienne Terblanche PhD Thesis

WW ET 15-01 – The impact of grape ripeness on wine style of cv. Pinotage – Final Report

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