Pinking of wine – influence of different winemaking processes, causative agents and pinking treatments
dc.contributor.advisor | Van Jaarsveld, Francois | en_ZA |
dc.contributor.advisor | Du Toit, Wessel J. | en_ZA |
dc.contributor.author | Nel, Anton Pieter | en_ZA |
dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. | en_ZA |
dc.date.accessioned | 2021-05-31T09:42:58Z | |
dc.date.available | 2021-05-31T09:42:58Z | |
dc.date.issued | 2021-03 | |
dc.description | Thesis (PhDAgric)--Stellenbosch University, 2021. | en_ZA |
dc.description.abstract | ENGLISH ABSTRACT: Pinking is a slight salmon-red discolouration in certain white wines after some oxygen ingress. This discolouration can lead to some economical loss to the winemaker. This phenomenon was first described in the late 1960s to the early 1970s. In the 50 odd years that this phenomenon is known, only about 4 peer-reviewed scientific articles were ever written with a handful of popular articles. In the first article on pinking, the researcher looked at how to test for pinking susceptibility (PS) as well as the influence of SO2 and pH on a pinked wine. This article established the method that is now used all over wine-producing countries. The influence of SO2 was established and the outcome was that the wine needs at least 40 mg/L of SO2 to protect the wine against PS. It was also established that the change in pH does not influence the pink colour showing that pinking is not associated with anthocyanins. In another article, preventative agents were researched. It was found that PVPP can bind certain compounds, presumably phenolic compounds, and settle them out, decreasing the PS. This research led to a phenomenal increase in the sale of PVPP. Literature indicated the possibility of anthocyanins in white wine and found malvidin-3-O-glucoside to play a role in PS of Siria grapes. In this study, the influence of temperature, skin contact time and pressing methods were researched on PS. Whole bunch press was tested against crushed & destemmed grapes. Dissolved oxygen (DO) was also measured to deduce the influence of oxygen on PS. The DO of the whole bunch pressed grapes was significantly higher than the crushed & destemmed grapes. This was due to more air space between the berries. Micro oxygenation in the initial stages of the winemaking practices led to a higher PS in the whole bunch pressed wines. The temperature had the highest influence on PS. Cooler (4ºC) grapes also had a significantly higher DO than grapes at ambient (20ºC) temperature. This finding was confirmed by different winemakers which had problems with pinking. All of them picked their Sauvignon blanc grapes at the coolest temperature, keeping them as cool as possible before processing. This and the higher DO in the juice help with the oxidation of the pinking precursors leading to a wine with a high PS. Longer skin contact time leads to a higher potential to pink, but this PS was not significant. When long skin contact time was combined with a cool temperature, the PS increases significantly. In two articles by Portuguese researchers, the presence of malvidin-3-O-glucoside was established. The theory that all cultivars have the genes to produce anthocyanins, but that the genes are repressed in white wines grapes, could hold some truth. In UV-visible spectrophotometric analysis, the spectra of pinked wines and control wines were analysed. The ranges where the differences in spectra were visible was not associated with any phenolic or anthocyanin compounds. During LC-MS analysis of the peaks showed that the compounds causing PS does not fit any of the known wine phenols. During the LC-MS analysis, the mass and retention times were given. The masses were compared to the library of the LC-MS and no fits to the mass data were established, thus making the identification of the compounds near impossible. A sensory analysis was done on pinked wines which are novel work and was never done before. The anecdotal evidence shows that pinked wine does not influence the aroma and taste. This was tested against a trained panel. It was found that the trained panel could not pick up the difference between a pinked wine and a control wine, although some of the tasters could pick up oxidation characters on the aroma. The sensory study showed that the panelists could pick up differences by smell but not on the taste of the wines. This study proved the anecdotal evidence and could lead to further sensory studies in the sensory science of pinked white wines. This study paved the way for further sensory research on pinked wines. The data also showed that panels can now be trained in identifying pink wine as a wine fault or to contribute a new style of wine to the public. | af_ZA |
dc.description.abstract | AFRIKAANSE OPSOMMING: Pienkwording1 in sommige wit wyne het 'n effense salmrooi verkleuring na aanraking met suurstof tydens sekere wynmaakprosesse. Hierdie verkleuring kan tot 'n ekonomiese verlies vir die wynmaker lei. Hierdie verskynsel is die eerste keer in die laat 1960's tot vroeë 1970's beskryf. In die om en by 50 jare wat hierdie verskynsel bekend is, is daar slegs ongeveer 4 wetenskaplike artikels en 'n handjievol populêre artikels geskryf. Die eerste artikel oor pienkwording het die navorser ondersoek ingestel na die toets metode van pienkwording, asook die invloed van SO2 en pH op 'n pienk wyn. In hierdie artikel word die metode bepaal wat nou algemeen in die wynproduserende lande gebruik word. Die invloed van SO2 is vasgestel en die resultaat wys dat die wyn minstens 40 mg/L SO2 benodig om die wyn teen pienkwording te beskerm. Daar is ook vasgestel dat die verandering in pH nie die pienk kleur beïnvloed nie, wat wys dat pienk nie met antosianiene geassosieer word nie. In 'n volgende artikel is die voorkomende middels teen pienkwording ondersoek. Daar is gevind dat Polivinielpolipirrolidoon (PVPP) die vermoë het om sekere verbindings, wat vermoedelik fenoliese verbindings kan wees, te bind en uit te skei. Hierdie navorsing het gelei tot 'n fenomenale toename in die verkoop van PVPP. Die laaste artikels het die moontlikheid van antosianiene in witwyn ondersoek. Die navorsers het malvidin-3-O-glukosied in Siria-druiwe gevind, 'n kultivar wat in Portugal afkomstig is. In hierdie navorsing is die invloed van temperatuur, dopkontak en persmetodes ondersoek. Heeltrospers is getoets teen ontstingelde en afgemaalde druiwe. Opgeloste suurstof (DO) is ook gemeet om die invloed van suurstof op pienkwording te meet. Die DO van die heeltrospers was aansienlik hoër as die ontstingelde en afgemaalde druiwe. Dit was as gevolg van meer lugruimte tussen die korrels. Suurstofopname in die beginfase van die wynmaakpraktyke, het gelei tot 'n hoër pienkwording in die heeltrosgepersde wyne. Temperatuur het die grootste invloed op pienkwording gehad. Koeler (4°C) geparste druiwe het ook 'n aansienlik hoër DO gehad as die omgewingstemperatuur (20°C). Hierdie bevinding was bevestig deur verskillende wynmakers wat pienkwordingsprobleme gehad het nadat Sauvignon blanc teen koeler temperature gepars was. Koel temperature en hoër DO in die sap het gehelp met die oksidasie van die pienkwordingsvoorgangers wat gelei het tot 'n wyn met 'n hoë pienkwordingspotensiaal. Dopkontak tyd het gelei tot 'n hoër pienkwordingspotensiaal, maar hierdie pienkwordingspotensiaal was nie betekenisvol nie. Wanneer lang dopkontak gekombineer word met koel temperature, neem die pienkwording aansienlik toe. In twee artikels deur Portugese navorsers was die teenwoordigheid van malvidin-3-O- glukosied vasgestel. Die teorie dat alle kultivars die gene het om antosianiene te produseer, maar dat die gene in witwyndruiwe onderdruk word, kan 'n mate van waarheid wees. In UV- sigbare spektrofotometriese analise is die spektra van pienkwyne en kontrolewyne geanaliseer. Die variasies wat deur die verskille in spektra sigbaar was, het nie verband gehou met enige fenoliese of antosianienverbindings in die wyn nie. Tydens vloeistofchromatografie- massaspektrometrie analiese was die pieke ontleed, maar die aangeduide pieke het nie by enige van die bekende wynfenole gepas het nie. 'n Sensoriese ontleding was op pienk wyne gedoen, wat nuwe werk was en nog nooit tevore gedoen is nie. Die anekdotiese bewyse toon dat pienk wyn nie die aroma en smaak beïnvloed nie. Dit is getoets deur 'n opgeleide proepaneel. Daar is gevind dat die opgeleide proepaneel nie 3die verskil tussen 'n pienkwyn en 'n kontrolewyn op smaak kon opspoor nie, maar dat sommige van die proeërs die pienkwyn op die aroma kon optel. Die opmerkings was dat hulle 'n bietjie oksidasie op die neus kon optel. | af_ZA |
dc.description.version | Doctoral | en_ZA |
dc.format.extent | 136 pages : illustrations (some color) | en_ZA |
dc.identifier.uri | http://hdl.handle.net/10019.1/110522 | |
dc.language.iso | en_ZA | en_ZA |
dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
dc.rights.holder | Stellenbosch University | en_ZA |
dc.subject | Pinking of white wine | en_ZA |
dc.subject | Sauvignon blanc wine -- Odour and Flavour | en_ZA |
dc.subject | Grapes -- Effect of temperature on | en_ZA |
dc.subject | Wine and wine making -- Chemistry | en_ZA |
dc.subject | UCTD | en_ZA |
dc.title | Pinking of wine – influence of different winemaking processes, causative agents and pinking treatments | en_ZA |
dc.type | Thesis | en_ZA |