The Impact of Smoke From Vegetation Fires on Sensory Characteristics of Cabernet Sauvignon Wines Made From Affected Grapes

Abstract

The increased incidence of vegetation fires near vineyards in the Western Cape, South Africa has led to growing concern over smoke taint in wine made from affected grapes. This study focused on the sensory properties of wines made from grapes that have been exposed to bushfire smoke. Cabernet Sauvignon grapes (ten days' post-véraison) were exposed to a single, hour-long treatment with smoke from burning fynbos under controlled conditions. The grapes were allowed to ripen and wines were then produced. Descriptive analysis of the wines was done for aroma and taste attributes. The results of the investigation show that the exposure of grapes to smoke during ripening led to sensory differences between wines made from different treatments, and that wines made from smoke-exposed grapes were perceived as having 'burnt', 'smoky' aromas and an 'ashy' aftertaste. Despite levels of free volatile phenols (VPs) being below or close to odour threshold levels for individual phenols, their combination led to a perception of the socalled 'burnt rubber' taint perceived in some South African red wines.

Review of the Effects of Grapevine Smoke Exposure and Technologies to Assess Smoke Contamination and Taint in Grapes and Wine

“…Furthermore, different woods vary in their lignin content, with Eucalyptus and Acacia vegetation species typically found in vegetation areas surrounding Australian vineyards containing high amounts of lignin [38]. Regardless of the fuel type, guaiacol and 4-methylguaiacol have been found to represent approximately 20% of the volatile phenolic compounds present in smoke [39]. Kelly et al [18] investigated smoke-derived volatile phenol concentrations in wine resulting from five different types of fuels with varying lignin compositions and found that guaiacol and 4-methylguaiacol represented approximately 20% of total phenols in wine for all fuel sources.…”

“…The amount of smoke contamination is a function of wind vectors, land topography, temperature gradients, and vineyards' proximity to the fire [44]. Once volatile phenols enter leaves and berries, they are rapidly metabolized into stable glycosidic forms [24,39,50]. These glycoconjugate precursors are hydrolyzed during fermentation, releasing them into their volatile forms, where they can impart their aromas into the resulting wine [23,51].…”

Techniques for Mitigating the Effects of Smoke Taint While Maintaining Quality in Wine Production: A Review

“…As smoke taint research has progressed, the range of volatile phenols that were measured as smoke taint markers evolved to include cresols, phenol, and syringols, in addition to guaiacol and 4-methylguaiacol, and analytical methods were developed to measure both free and bound (glycosylated) volatile phenols [ 27 , 33 , 40 ]. Several studies have attempted to establish the sensory contributions of smoke-derived volatile phenols [ 41 , 42 , 43 ]; while the volatile phenol glycoconjugates that remain in wine after fermentation [ 33 , 44 ] are thought to contribute to the ashy aftertaste perceived in some smoke-tainted wines, due to in-mouth hydrolysis [ 45 ]. Nevertheless, it is reasonable to expect that additional smoke taint marker compounds might be identified in the future.…”

Classification of Smoke Contaminated Cabernet Sauvignon Berries and Leaves Based on Chemical Fingerprinting and Machine Learning Algorithms

“…However, it is interesting that the low smoke treatment (LS) had lower g s than the high smoke with misting treatment (HSM), which indicates that misting may have reduced the effect of smoke exposure on g s . During a bushfire, the type of fuel burnt will vary depending on the region and the type of plant species native to the area, as well as the amount of smoke exposure due to land topography and wind vectors; therefore, the effect on g s may vary [ 17 , 18 , 23 , 66 ]. While misting only partially prevented the uptake of volatile phenols and glycoconjugates in grapes [ 60 ], it did appear to have a physiological effect.…”