IVAS 2022 banner
IVES 9 IVES Conference Series 9 IVAS 9 IVAS 2022 9 Controlling Wine Oxidation: Effects of pH on Key Reaction Rates

Controlling Wine Oxidation: Effects of pH on Key Reaction Rates

Abstract

Acidity is often touted as a predictor of wine ageability, though surprisingly few studies have systematically investigated the chemical basis for this claim. The effects of pH on the rates of several key reactions in the wine oxidation pathway were evaluated in model wine. Wine oxidation starts with the redox cycling of iron between two oxidation states: iron(II) is oxidized by oxygen while iron(III) is reduced by phenols. While iron(III) reduction slowed as pH was increased from 3 to 4, oxygen consumption by iron(II) accelerated. However, pseudo-first order rate constants for oxygen consumption remained at least ten times lower than those of iron(III) reduction, suggesting that iron(II) oxidation is the rate-determining reaction for wine oxidation, and wine aging is thus limited by oxygen ingress. Despite this, different wines subject to the same oxidative conditions will often vary in their rate of maturation, indicating another control point “downstream” in the oxidation pathway. Hydrogen peroxide formed upon the reduction of oxygen can react in one of two ways: the iron-catalyzed Fenton oxidation of ethanol into acetaldehyde, or quenching by sulfur dioxide. Acetaldehyde production from added H2O2 was faster at pH 4 than at pH 3, while the efficacy of SO2 as an antioxidant was diminished, lending credence to the notion that high-pH wines deteriorate more quickly than more acidic wines. These observations may be explained by the pH-dependent complexation of iron by tartrate and other carboxylic acids in wine, which determines the reduction potential of iron and controls its reactivity. Findings overall suggest viticultural and winemaking practices, as they pertain to the management of wine acidity, may have significant long-term repercussions on aging.

DOI:

Publication date: June 23, 2022

Issue: IVAS 2022

Type: Article

Authors

Nguyen Thi1

1Weincampus Neustadt, Institute for Viticulture and Oenology, Dienstleistungszentrum Ländlicher Raum (DLR), Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany

Contact the author

Keywords

wine ageing, oxidation, iron, acidity, Fenton

Tags

IVAS 2022 | IVES Conference Series

Citation

Related articles…

Elevational range shifts of mountain vineyards: Recent dynamics in response to a warming climate

Increasing temperatures worldwide are expected to cause a change in spatial distribution of plant species along elevational gradients and there are already observable shifts to higher elevations as a consequence of climate change for many species. Not only naturally growing plants, but also agricultural cultivations are subject to the effects of climate change, as the type of cultivation and the economic viability depends largely on the prevailing climatic conditions. A shift to higher elevations therefore represents a viable adaptation strategy to climate change, as higher elevations are characterized by lower temperatures. This is especially important in the case of viticulture because a certain wine-style can only be achieved under very specific climatic conditions. Although there are several studies investigating climatic suitability within winegrowing regions or longitudinal shifts of winegrowing areas, little is known about how fast vineyards move to higher elevations, which may represent a viable strategy for winegrowers to maintain growing conditions and thus wine-style, despite the effects of climate change. We therefore investigated the change in the spatial distribution of vineyards along an elevational gradient over the past 20 years in the mountainous wine-growing region of Alto Adige (Italy). A dataset containing information about location and planting year of more than 26000 vineyard parcels and 30 varieties was used to perform this analysis. Preliminary results suggest that there has been a shift to higher elevations for vineyards in general (from formerly 700m to currently 850 m a.s.l., with extreme sites reaching 1200 m a.s.l.), but also that this development has not been uniform across different varieties and products (i.e. vitis vinifera vs hybrid varieties and still vssparkling wines). This is important for climate change adaptation as well as for rural development. Mountain areas, especially at mid to high elevations, are often characterized by severe land abandonment which can be avoided to some degree if economically viable and sustainable land management strategies are available.

Toasted Vine-Shoots As An Alternative Enological Tool. Impact On The Sensory Profile Of Tempranillo Wines

The use of toasted vine-shoots as an alternative enological tool to make differentiated wines has generated interest among researchers and wineries. However, the evolution of these wines in bottle and the effect on the sensory profile has not been studied so far.

Implications of grapevine row orientation in South Africa

Row orientation is a critical long-term viticulture practice, which may have a determining effect on grape and wine quality as well as cost efficiency on a specific terroir selected for cultivation.

Characterisation of viticultural and oenological practices in two French AOC in the middle Loire Valley: comparison of different methods to extract information from a survey among winegrowers

The type of wine is determined by environmental, plant materials and human factors. These factors are numerous and interact together, which makes it difficult to determine the hierarchy of their effects

FOLIAR APPLICATION OF METHYL JASMONATE AND METHYL JASMONATE PLUSUREA: INFLUENCE ON PHENOLIC, AROMATIC AND NITROGEN COMPOSITION OFTEMPRANILLO WINES

Phenolic, volatile and nitrogen compounds are key to wine quality. On one hand, phenolic compounds are related to wine color, mouthfeel properties, ageing potential. and are associated with beneficial health properties. On the other hand, wine aroma is influenced by hundreds of volatile compounds. Fermentative aromas represent, quantitatively, the wine aroma, and among these volatile compounds, esters, higher alcohols and acids are mainly responsible for the fermentation bouquet.