Amelioration of smoke taint in wine using commercially available and legally permissible additives

Langa, Nongcebo Portia (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The changes experienced in climate in many parts of the world have led to an increase in incidences of wildfire, and it has been predicted that these events will become more prevalent over time. All fires release volatile compounds into the atmosphere, and if they occur near vineyards where grapes are ripening, smoke taint may be detected in wines made from these grapes. Smoke taint is a critical issue for wine producing regions of the world as smoky and unpleasant flavours and aromas are perceived in affected wines, and this may have serious economic implications for producers. A number of researchers have tried to understand smoke taint, and their research has shown that volatile phenols (VP) are chemical compounds responsible. Additional research has revealed that although guaiacol, 4-ethylguaiacol, and 4-methylguiacol were originally identified as chemical markers of smoke taint, other VPs such cresols, eugenol, and phenol derivatives also play a role in causing smoky and ashy flavours. Strategies to eliminate the problem have ranged from washing the grapes and harvesting by hand, to minimising skin contact and choosing yeast and bacteria for minimal impact, and marketing wines for early release. These techniques work but do not eliminate an important underlying issue: glycoconjugates. Glycoconjugates or glycosides (VPs bound to sugars) are compounds that act as precursors of smoke taint produced as a detoxification by-product by vines. Glycosides can be hydrolysed by acid and enzymes, which means wines have the potential to increase available VPs in the wine, despite great care being taken to minimise VPs. This study expands on previous strategies that have been used to ameliorate smoke taint by using commercially available and legally permissible products in South Africa and exploring their effectivity at different dosage levels. Grapes in this study were harvested and deliberately smoked in crates using a bee-smoker, which produced smoke generated from fynbos (indigenous vegetation) and pine needles. Activated charcoal, oak extract, polymer powder were used in the first part of this study to try and ameliorate the taint during winemaking. GC-MS analysis of treated wines and controls revealed that only activated charcoal at elevated levels decreased VPs chemically. Sensory analysis of treated wines and controls by a trained panel using Descriptive Analysis showed that oak extract did increase levels of eugenol and consequently increased the ‘woody’ attribute, thus somewhat masking the smoke aroma. None of the treatments were able to remove the smoke aroma and flavour satisfactorily, primarily because of ashy flavour on the palate, likely due to in-mouth enzymes hydrolysing VP-glycosides. Building on the data and knowledge accumulated during the first part of the study, the second part of the study attempted to reduce levels of volatile phenol glycosides by using β-glucosidases before treatment application for removing free volatiles (“release-and-remove”). The treatments used after the enzyme hydrolysis were activated charcoal, polymer powder, yeast hulls, and mannoproteins. Chemically, GC-MS showed that there were sharp increases of VPs after the addition of enzymes, and some success in subsequent removal of the free volatiles. Further work is needed to determine the optimum levels of treatment. The data in this study showed potential for β-glucosidases to be used in the winemaking process, not only to release VPs (for later removal) but to increase the expression of fruity aromas in the wine. Enzymes may help to release other compounds that contribute to wine flavour, thus masking some of the smoke taint. This study contributes to the improved understanding of methods that can be used for the removal or treatment of smoke taint, but the need for further work was highlighted. The use of β-glucosidases followed by multiple finings could be an option for producers after a fire incident has occurred near a vineyard during ripening of grapes.

AFRIKAANSE OPSOMMING: Die klimaatsveranderinge wat in baie dele van die wêreld ervaar word, het gelei tot ’n toename in die gevalle van veldbrande en daar is voorspel dat sulke gebeure met tyd sal toeneem. Alle brande stel vlugtige verbindings in die atmosfeer vry en as hulle naby wingerde plaasvind waar druiwe ryp word, kan ’n rooksmaak in die wyn geproe word wat met hierdie druiwe berei is. ’n Rooksmaak is ’n kritiese kwessie vir die wynproduserende dele van die wêreld omdat rokerige en onaangename geure en aromas in die geaffekteerde wyne bespeur kan word en dit kan ernstige ekonomiese implikasies vir die produsente inhou. ’n Aantal navorsers het probeer om die rooksmaak te begryp en hulle navorsing toon dat vlugtige fenole (VF) die chemiese verbindings is wat daarvoor verantwoordelik is. Bykomende navorsing het getoon dat alhoewel guajakol, 4-etielguajakol en 4-metielguajakol aanvanklik geïdentifiseer is as chemiese merkers van die rooksmaak, speel ander VF’s, soos kresole, eugenol en fenol derivate ook ’n rol in die veroorsaking van rokerige en asgeure. Strategieë om die probleem uit te skakel, wissel van die was van die druiwe en oes met die hand tot die vermindering van dopkontak, om gis en bakterieë met ’n minimale impak te kies en bemarking van die wyn vir vroeë vrystelling. Hierdie tegnieke werk wel, maar skakel nie ’n belangrike onderliggende kwessie uit nie: glikokonjugate. Glikokonjugate of glikosiede (VF’s verbind aan suikers) is verbindings wat optree as voorlopers van die rooksmaak wat geproduseer word as ’n detoksifikasie byproduk van die wingerdstokke. Glikosiede kan deur suur en ensieme gehidroliseer word, wat beteken dat wyn die potensiaal het om die beskikbare VF’s in die wyn te verhoog, ten spyte van sorg wat geneem word om VF’s te verminder. Hierdie studie brei uit op vorige strategieë wat gebruik is om rooksmaak te verminder deur kommersieel beskikbare en wetlik toelaatbare produkte in Suid-Afrika te gebruik en hulle doeltreffendheid by verskillende dosisse te ondersoek. Die druiwe vir hierdie studie is geoes en opsetlik met behulp van ’n rookpomp in kratte gerook, met rook wat deur fynbos (inheemse plantegroei) en dennenaalde gegenereer is. Geaktiveerde steenkool, eik-ekstrak en polimeerpoeier is in die eerste deel van die studie gebruik om te probeer om die rooksmaak tydens wynbereiding te verminder. GC-MS analise van die behandelde wyne en kontroles het getoon dat slegs geaktiveerde steenkool teen verhoogde vlakke die VF’s chemies kon verminder. Sensoriese analise van die behandelde wyne en kontroles deur ’n opgeleide paneel m.b.t. beskrywende analise het getoon dat die eike-ekstrak die vlakke van eugenol verhoog het en gevolglik die ‘houtagtige’ eienskap verhoog het, wat in ’n mate die rook-aroma verbloem het. Geen van die behandelings kon die rook-aroma en geur doeltreffend verwyder nie, hoofsaaklik as gevolg van die asgeure in die palet, moontlik as gevolg van binnensmondse ensieme wat VF-glikosiede hidroliseer. Op grond van die data en kennis wat tydens die eerste deel van die studie verkry is, het die tweede deel van die studie gepoog om die vlakke van vlugtige fenolglikosiede te verminder deur gebruik te maak van β-glukosidases voor die toepassing van die behandeling om vry vlugtige verbindings te verwyder. Die behandelings wat ná ensiemhidrolise gebruik is, was geaktiveerde steenkool, polimeerpoeier, gisdoppe en mannoproteïene. Chemies het GC-MS getoon dat daar skerp toenames in VF’s was ná die byvoeging van ensieme, en ’n mate van sukses in die gevolglike verwydering van vry vlugtige verbindings. Meer werk word benodig om die optimum vlakke van die behandeling te bepaal. Die data in hierdie studie het die potensiaal getoon vir β-glukosidases om in die wynbereidingsproses gebruik te word, nie net om VF’s vry te stel nie (vir latere verwydering) maar ook om die uitdrukking van vrugtige aromas in die wyn te verhoog. Ensieme kan help om ander verbindings vry te laat wat ’n bydrae kan maak tot wyngeur en wat kan help om ’n mate van die rooksmaak te verbloem. Hierdie studie dra by tot ’n verbeterde begrip van metodes wat gebruik kan word vir die verwydering of behandeling van rooksmaak, maar ’n behoefte aan verdere werk is uitgelig. Die gebruik van β-glukosidases gevolg deur veelvoudige brei is ’n moontlike opsie vir produsente nadat daar ’n brand naby ’n wingerd was terwyl die druiwe besig was om ryp te word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105837
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