Modelling Smoke Flavour in Wine from Chemical Composition of Smoke-Exposed Grapes and Wine

Abstract

Wine grapes exposed to smoke and wine made from grapes exposed to smoke can robustly be identified through their elevated concentrations of volatile phenols and phenolic glycosides serving as smoke markers, compared to concentrations typically found in non-smoke-exposed samples. Smoke-affected wines with high concentrations of volatile phenols and glycosides can have smoky flavours, but the relationship between concentrations of specific smoke markers in grapes and the intensity of smoky sensory attributes in the resulting wine has not been established. This study sought to determine whether volatile phenols and glycoside concentration in grapes and wine are suited to predict smoke flavour, to identify the key drivers of smoke flavour in both matrices. The study aimed to determine what concentrations of volatiles and glycosides in grapes impart an unacceptable smoke flavour in the resulting wine, to provide a guide for producers assessing suitability of smoke-exposed grapes for wine production. During vintage 2020, a total of 65 grape samples were collected from vineyards exposed to bushfire smoke, as well as unaffected vineyards. Chardonnay, Pinot Noir, and Shiraz grapes were harvested from vineyards in New South Wales, South Australia, and Victoria. Unoaked wines (50 kg scale) were produced under controlled conditions. The wines had a wide range of smoke flavour intensities rated by a trained sensory panel. Statistical models based on guaiacol, o-cresol, m-cresol, p-cresol, and some glycosides gave good predictions of smoke flavour intensity, with a slightly different optimal model for each cultivar. Subsequently, critical concentrations for quality defects were estimated to provide a guide for producers. A subset of smoke exposure markers in wine grapes affected by smoke from bushfires can be used to predict the degree of smoke flavour in wine. This information provides a first guide for assessing the risk of producing smoke tainted wine from smoke-exposed grapes.

Volatile Organic Compound-Based Predictive Modeling of Smoke Taint in Wine

“…Recently, a study that models the smoke taint flavor based on the VOC concentration in Australian grapes and wine using the Partial Least Squares approach for each variety with listing the VOCs that significantly contribute the smoke flavor is published. 31 Some VOCs, especially free guaiacol, significantly contribute to or are correlated with the smoke taint flavor in both studies; however, some VOCs are not, such as m-cresol. This study which includes the VOC concentration from more varieties of wine and grape samples in California and Oregon may allow us to discover how smoke taint affects the wine quality in different regions and varieties.…”

“…In this study, a complete data set that combines VOC concentrations of wine and grape samples from different varieties and smoke taint index is prepared, and it allows us to discover the VOC composition changes and the correlation between VOC concentrations and smoke taint index and to apply predictive modeling of the smoke taint index at the same time. Recently, a study that models the smoke taint flavor based on the VOC concentration in Australian grapes and wine using the Partial Least Squares approach for each variety with listing the VOCs that significantly contribute the smoke flavor is published . Some VOCs, especially free guaiacol, significantly contribute to or are correlated with the smoke taint flavor in both studies; however, some VOCs are not, such as m -cresol.…”

“…In recent years, machine learning algorithms as a part of the Artificial Intelligence (AI) have increasingly been applied in food science and agriculture for a sustainable food system, including predicting micronutrients, − creating food ontologies and knowledge bases, precision agriculture, and crop and animal management . Although VOCs in smoke-affected grapes and wine have been reported, the levels contributing to the smoke taint effect of VOCs have been evaluated, and a few studies that model the smoke flavor based on chemical composition have been published recently, the number of studies focusing on data-driven approaches, especially predictive modeling of smoke taint based on VOC concentrations, are still limited.…”

Smoky Characters in Wine: Distinctive Flavor or Taint?

“…This rejection concentration of guaiacol is, however, much higher than the concentration observed in many "smoke-tainted" wines. 11 Hence, relying on guaiacol measures would likely result in a large number of false-negative classifications of wine samples as "fault-free", while, in fact, they can be recognized as smoke tainted when assessed by sensory evaluation. Similar to guaiacol, a number of other common wine flavor compounds are known that might be present in non-smoke-affected wines, such as volatile thiols PMT and 2-FMT and 4-ethyl phenol, and can confer characters that could be confused with smoke taint, such as "medicinal", "burnt rubber", "empyreumatic", and "leather".…”

“…At the same time, it was recognized that a substantial proportion of moderately smoke-exposed grape samples, especially from white varieties, will not inevitably give tainted wine. 11 While it has been shown that the concentrations of smoke-related phenols and glycosides in grapes can be used to predict "smoke" flavor intensity in wine, 11 it remains challenging to differentiate between smokeexposed grapes that may just yield recognizable but acceptable "smoky" characters and grapes that will, with a known degree of certainty, result in "smoke-tainted" wine that is unfit for sale. Hence, this perspective explores which concentrations of aroma compounds might lead to distinctive "smoky" characters versus those which could contribute to unacceptable smoke taint in wine.…”