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

Terblanche, Etienne Louis Adriaan (2019-04)

Thesis (PhDAgric)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Ons begrip van die wingerd se reaksie op omgewingsfaktore en die daaropvolgende druif- en wynsamestelling en sensoriese profiel vorm die grondslag waarop wynprodusente hul produkgebaseerde/markverwante verbouingsbesluite maak. Ondanks bogenoemde is daar verbasend min inligting vir produsente beskikbaar ten opsigte van verwagte verandering in wynstyl gekoppel aan rypheidsvlakke. Die hoofdoelstelling van hierdie beskrywende studie was dus om ‘n verwysingsbron daar te stel om produsente rakende oesbesluite behulpsaam te wees. Vitis vinifera L. cv. Pinotage, ‘n Suid Afrikaanse kultivar, is gebruik in die studie as gevolg van sy vroeë en vinnige suiker-akkumulasie, analoog aan die verwagte wingerdreaksie as gevolg van klimaatsverwarming. In hierdie veldstudie is die omvang van druif- en wynsamestelling veranderings asook die sensoriese profiel veranderings van cv. Pinotage by vyf (R1-R5) rypheidsgrade, soos gedefinieer deur suikervlakke/Brix (ca. 21, 23, 25, 27 & 29 ˚B), gemeet oor drie oesjare (2015-17) en op twee liggings met Pinotage/140 Ruggeri (A) en Pinotage/1130 Paulsen (B), onder Mediterreense klimaatsomstandighede (nie-besproei) in die Wes-Kaap, Suid Afrika. Die onbesproeide wingerd wat op droogtebestande onderstokke geënt is, het goed (op ‘n fisiologiese vlak) by lae seisoenale reënval en hoë gemiddelde temperature aangepas. Desondanks die agteruitgang/veroudering van die lower tydens laat rypwording, is die volle spektrum rypheidsvlakke (R1-R5) binne 21 dae voltooi. Korrelgrootte was deurgaans konstant by R1-R4 en verhoging of afname in korrelinhoud was dus grootliks onafhanklik van die konsentrasie-effek as gevolg van afname in korrelgrootte/dehidrasie (hoër dop:pulp verhouding), aangesien dit slegs by R5 voorgekom het. Die laat-seisoen afname in korrelgrootte (dehidrasie) by R5 het ‘n verhoging in primêre metaboliete (suikers en sure) en minerale, maar verlaging in fenoliese en antosianien inhoud tot gevolg gehad. Die konsentrasie fenoliese verbindings en antosianiene het van R1-R4 (piek) verhoog, voordat dit by R5 afgeneem het. Veranderinge in die aromatiese profiel van die druiwe was subtiel en die reaksie van sleutelkomponente is merkbaar deur Oesjaar en Ligging beïnvloed. Resultate dui op ‘n relatiewe lae verskuiwing in die totale druifaroma profiel per rypheidsgraad gedurende die kompakte oestydperk (21 dae). Bogenoemde in ag genome, het die vlugtige komponente (aroma) van die wyn duidelike definisie ten opsigte van rypheidsvlakke getoon, met onderskeibare veranderinge vir komponente van verskillende chemiese groepe. Dis belangrik om daarop te let dat bekende impak geure van Pinotage, soos byvoorbeeld isoamiel asetaat (piesang), etiel oktanoaat (soet vrugtig/blomme) en ß-damasenoon (pruim), rypheidsvlak-verwante veranderings getoon het. Hierdie veranderinge in die aromaprofiel is ook deur geurbeskrywende terme en hul intensiteit in sensoriese analises, getoon. Daarbenewens speel veral smaakbeskrywende terme, insluitende suurheid, volheid, vrankheid, alkohol en konsentrasie, wat ooreenstem met basiese vrug-chemie (suiker, titreerbare suur en pH) ‘n dikterende rol in die algehele sensoriese profiel. Hierdie omvattende druifsamestelling veldstudie plaas rypwordingverwante veranderinge in konteks met dié wat deur die omgewing (Oesjaar/Klimaat) en Ligging (Grond & Genotipe) teweeggebring/beïnvloed word. Dit wys op die negatiewe effek van ‘n verlengde druiwe hangtyd en verskaf noodsaaklike insigte rakende wynsamestelling veranderinge gedurende vinnige suiker akkumulering. Nuwe en eiesoortige inligting ten opsigte van potensiële wynstyle, soos geonderskei deur verskillende rypheidsvlakke, is ingewin. Hierdie inligting kan maklik deur produsente benut word om die gewenste produkdoelwit te bereik.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106248
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