Winetech Technical Yearbook 2022

and pungent variety of flora, it also needs to burn to survive. Fire is essential to maintain the healthy vegetation dynamics promoting synchronous germination and sprouting of bulbs, rhizomes and woody species. Periodic wildfires (veldfires to us South Africans) are a natural phenomenon in fynbos areas with a frequency of one to 40 years, although fire occurrence has increased a lot over the decades due to human activity. 3 Fynbos fires are rapid and fairly cool, moving very fast over mountainous regions with the assistance of often gale-force South Easterly winds in summer. Vineyards are located all over the province and are frequently in the path of these bushfires during their peak ripening season in February and March when the veld is at its driest, and fire risk is high. These veldfires are accompanied by smoke that can cover hundreds of square kilometres. Anyone who believes that fires (even under Covid lockdown conditions that restrict human activity) are not a problem in the Cape, only needs to look at the smoke plume covering the winelands in the NASA image (figure 1) taken on 26 February last year. 4 This fire was in the Jonkershoek moun tains, a fair distance from human habi tation, and yet the smoke plume choked Franschhoek, Stellenbosch, the Helder berg and even extended as far as Durban ville, all prime viticultural areas where grapes were ripening on the vines. The fire burned 33 000 hectares, the smoke drifted over vineyards for around a week, and a number of prominent producers were affected. Although large in area, this Western Cape fynbos fire event was defi nitely not unusual. Veldfires emit large amounts of volatile compounds and particles and these emissions can significantly influence the chemical composition of the atmosphere in the region. The impact of wildland fires depends on meteorology, fire plume dynamics, the amount and chemical composition of the emissions, as well as land use history and environmental conditions, so it is difficult to predict what will happen in any given veld fire event. We also know very little about the specific emission characteristics (smoke quality and character) of fynbos. What we do know is that VPs like guaiacol, 4-methyl guaiacol, 4-ethyl phenol and the cresols are well known as smoke components in most fire events, and have been shown to be absorbed by grapes, and carried through to wine 5 where they manifest as smoky, burnt aromas and an ashy taste (figure 2). Not only is the effect of the smoke difficult to predict, it’s also very difficult to manage smoke compounds once they are present in the wine. The VPs can be volatile, but they can also be locked up as glycosides (non-volatile compounds) that are released during winemaking and ageing. The wine matrix also influences how easily the VPs can be perceived. Add

FIGURE 1. Jonkershoek fire, 26 February 2021. Red colour in the figure shows the active fire region. Satellite photo, NASA. (Gabbert, 2021.)

AUSTRALIA VERSUS BORDEAUX Coming back to the Jacob’s Creek example, we see quite another set of factors in the terroir effect. External or exogenous factors may not cause a grapevine response, but they are certainly present in wine, and are arguably every bit as important as an expression of terroir as the endogenous factors. Analysis of Aussie Cabernets has revealed varying concentrations of eucalyptol in wines from different regions within Australia, prompting the researchers to suggest that this compound could help characterise terroir. At the International Terroir Congress in 2020, Capone 2 demonstrated that Aussie wines also have far higher levels of eucalyptol than Bordeaux Cabernets, so it’s definitely an “Australian thing”. MICROBIAL TERROIR Another important exogenous factor in terroir expression is the microbes found on grape berries when they are harvested. These microorganisms originate from the vineyard and are present in the crush. The initial steps in fermentation are carried out by many non- Saccharomyces yeast genera, which produce a wide range of higher alcohols and esters. This may explain why Coonawarra wines were found by Capone and the team to have ‘liquorice’, ‘dark fruit’ and ‘spice’, traits associated with hexanol, ethyl propanoate and ethyl butyrate, whereas Yarra Valley wines are described as ‘red fruit’ and ‘jammy’, due to the presence of 1-octanol, 2-octanone and dimethyl sulphide. A cluster of wines from Margaret River were also characterised by ‘grassy’, ‘savoury’ and ‘chocolate’ aromas, which were probably due to the presence of ethyl decanoate, butan-1-ol, (Z)-3 hexen-1-ol and ethyl-3-methyl butanol.

Each Australian region seemed to have some unique aroma attributes, as well as the common cultivar characteristics. The unique microbiome in each terroir may well have a lot to do with it. ZOOMING IN ON VOLATILE PHENOLS The volatile phenols (VPs) are yet another exogenous factor that could be considered an important aspect of terroir expression. The two VPs, 4-ethyl phenol (4-EP) and 4-ethylguaiacol (4-EG), are part of a large group of compounds that are associated with smoke taint in wine, but 4-EP and 4-EG can also come from Brettanomyces spoilage (‘Brett’). They are found in significantly higher concentrations in Bordeaux wines than in Australian wines. The characteristic ratio (4-EP: 4-EG = 8:1) that is symptomatic of Brett appeared to account for their presence in the French wines tested by Capone and her colleagues, giving a range of ‘earthy’ and ‘yeasty’ aromas, which can be typical of Bordeaux blends. The point of all this is that different regions do give us different wine chemistry, not all of them are related directly to the grape itself. Some of the effects that we see that give wines their regional typicality are related to external factors (eucalyptus leaves and Brettanomyces for starters). So why don’t we use this terroir-chemistry relationship to nail down the uniqueness and authenticity of our own wine region? SO, WHAT’S UNIQUE ABOUT OUR TERROIR? Easier to ask what isn’t unique! In the Western Cape, we have fynbos , the world’s richest and smallest floral kingdom. Other than the fact that fynbos contain a rich

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WINETECH TECHNICAL YEARBOOK 2022