Study of Durif (Vitis vinifera L.) berry ripening phases in relationship to wine styles

Wiid, Stephanie Cezanne (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The wines of Durif (Petite Sirah) are known for their exceptionally dark colour and astringency (mouth feel). The goal of this research project was to assess Durif wine styles, profiles and diversity using sequential harvest. Grapes were harvested from a Durif vineyard in Paarl, South Africa, at different stages of ripeness on different dates (sequential harvesting) influencing the grape composition, which, in turn, influences wine composition and sensory attributes. There is not only one optimal harvest date for a vineyard or specific site and several harvest dates could be adequate. This research project spanned the 2012 and 2013 vintages. The 2012 was used as a diagnostic year to characterize the vineyard plot and the options for harvest timing. Sequential harvesting was used to determine if Durif follows a berry aromatic evolution (Deloire, 2011). The berry aromatic evolution describes wine styles, which can be achieved by determining harvest time/period using sugar loading as a berry physiological indicator. These wine styles include a fresh fruit (FF) style, a neutral, spicy or pre‐mature fruit style, a mature fruit (MF) style and later an over ripe style (OR). One of the major findings of this research project was calibrating the model of berry sugar accumulation for Durif to determine picking windows/dates for specific wine styles. The wines made from sequentially harvested grapes were sensorially assessed using the citation frequency method (Campo et al., 2010).The sensory analysis was used to find the sensory attributes of wines from two harvest time points corresponding to fresh fruit and mature fruit style wines. The main aromatic attributes associated with Durif wines in South Africa were identified. Descriptive analysis was used to rate the intensity of astringency, bitterness, sweetness, sourness and alcohol perception of the wines and how it changes with harvest timing Berry composition was analysed (fructose, glucose, tartaric acid, malic acid, total anthocyanins and total phenolics) and it was shown that there were significant changes in berry composition during ripening. The evolution of berry composition during the ripening period highlights the importance of optimization of the picking date. The wine composition, however, is not directly related to grape composition as it is compounded by the impact of extraction during fermentation (with increasing levels of ethanol with increasing sugar levels when using sequential harvesting) on tannin and anthocyanin extractability and yeast metabolism (Gil et al., 2015, Fournand et al., 2006). Must composition (pH, TA, Brix) was monitored and showed significant differences between early and later harvest dates. Wine composition of each sequentially harvested wine was analysed. From the trends observed in the frequency of citation method it is suggested that the berry aromatic ripening sequence for Durif exists and fresh or mature fruit style wines can be made. Harvest timing could be defined as picking ten days after the keypoint to produce fresh fruit style wines and twentythree days to produce mature fruit style wines according to the results of the 2013 vintage.

AFRIKAANSE OPSOMMING: Wyne afkomstig van Durif (Petite Sirah) is bekend vir hulle buitengewoon donker kleur en vrankheid (mondgevoel). Die doelwit van hierdie navorsingsprojek was om die wynstyle, ‐profiele en ‐diversiteit van Durif met behulp van opeenvolgende oes te bepaal. Die druiwe is in ’n Durif‐wingerd in die Paarl, Suid‐Afrika, op verskillende rypheidstadiums en op verskillende datums geoes (opeenvolgende oes), wat die druifsamestelling beïnvloed het en wat op sy beurt weer wynsamestelling en sensoriese kenmerke beïnvloed het. Daar is nie net een optimale oesdatum vir ’n wingerd of spesifieke ligging nie en etlike oesdatums sou voldoende kan wees. Hierdie navorsingsprojek is in die 2012 en 2013 oesjare onderneem. Die diagnostiese jaar was 2012 en is gebruik om die wingerdblok te karakteriseer en die opsies vir die tyd van oes te bepaal. Opeenvolgende oes is gebruik om te bepaal of Durif aromatiese evolusie in die korrel ondergaan (Deloire, 2011). Die aromatiese evolusie van die korrel beskryf wynstyle wat bekom kan word deur die oestyd/tydperk te bepaal op grond van suikerlading as ’n aanduier van korrelfisiologie. Hierdie wynstyle sluit in vars vrugte (fresh fruit (FF)), neutraal, speseryagtig of voorryp, volwasse vrug (mature fruit (MF)) en later oorryp (overripe style (OR)). Een van die vernaamste bevindinge van hierdie navorsingsprojek was die kalibrasie van ’n model van suikerophoping in die korrel vir Durif om die plukvensters/datums vir spesifieke wynstyle te bepaal. Die wyne wat met die opeenvolgend geoeste druiwe gemaak is, is sensories geanaliseer d.m.v. die aanhalingsfrekwensiemetode (citation frequency method) (Campo et al., 2010). Sensoriese analise is gebruik om die sensoriese eienskappe te bepaal van wyne afkomstig van twee spesifieke oestye wat ooreenstem met die vars vrug en volwasse vrug wynstyle. Die vernaamste aromatiese bydraers wat verband hou met Durif‐wyne in Suid‐Afrika is geïdentifiseer. Beskrywende analise is gebruik om die intensiteit van vrankheid, bitter, suurheid en alkoholwaarneming van die wyne te beoordeel en hoe dit met die tyd van oes verander. Korrelsamestelling is geanaliseer (fruktose, glukose, wynsteensuur, appelsuur, totale antosianiene en totale fenoliese stowwe) en daar is getoon dat noemenswaardige veranderinge in korrelsamestelling tydens rypwording plaasgevind het. Die evolusie van korrelsamestelling tydens die rypwordingstydperk bring die belangrikheid na vore om die plukdatum te optimaliseer. Wynsamestelling hou egter nie direk verband met druifsamestelling nie, aangesien dit versterk word deur die impak van ekstraksie tydens gisting (met toenemende vlakke van etanol tesame met toenemende suikervlakke wanneer opeenvolgende oes gebruik word) op die ekstraheerbaarheid van tannien en antosianien en op gismetabolisme (Gil et al., 2015, Fournand et al., 2006). Mossamestelling (pH, TA, Brix) is gemonitor en het noemenswaardige verskille getoon tussen die vroeër en later oesdatums. Die wynsamestelling van elke opeenvolgend geoeste wyn is geanaliseer. Vanuit die tendense wat in die aanhalingsfrekwensiemetode waargeneem is, word daar voorgestel dat daar ’n korrel aromatiese rypwordingsopeenvolging vir Durif bestaan en dat vars en volwasse wynstyle verkry kan word. Volgens die resultate vanaf die 2013‐oesjaar kan die tyd van oes gedefinieer word as pluk tien dae ná die sleutelpunt om vars wynstyle te produseer en drie‐en‐twintig dae daarna om volwasse wynstyle te produseer.

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