Winetech Technical Yearbook 2022

2022 TECHNICAL YEARBOOK

AUTHORS ...................................................................................... 3 FOREWORD . .............................................................................. 4 VITICULTURE . ......................................................................... 6 Petri disease – when and how do Western Cape vineyards get infected?. ............................................................................................. 7 Smokin’ hot Western Cape terroir (Part 1)................................................ 9 Smokin’ hot Western Cape terroir (Part 2).............................................. 12 Impact of grapevine leafroll disease on grape and wine composition...... 14 Optimisation of grapevine leafroll detection by sentinel canes................ 18 Hot water treatment – effective eradication of root-knot nematodes? . ... 23 Hyperspectral – the answer to water stress? (Part 1).............................. 24 Hyperspectral – the answer to water stress? (Part 2).............................. 27 The CRISPR revolution and grapevine. .................................................. 29 Transmission dynamics of grapevine leafroll-associated virus 3 (GLRaV-3) variants ................................................................................. 32 High altitude vineyards........................................................................... 35 The bud (erinose) mite – identity crisis. ................................................. 38 OENOLOGY ............................................................................... 40 Cooling Sauvignon blanc grapes before processing – is it worth the effort, time and energy? .................................................... 41 The effect of aeration on spontaneous Chardonnay fermentations .......... 43 Elemental sulphur residues at harvest – boosting both the good and the bad. ....................................................... 44 Factors affecting sparging efficiency (Part 1) . ......................................... 46 Factors affecting sparging efficiency (Part 2) . ......................................... 48 Why does my wine smell like mushrooms?. ........................................... 50 Cork or crown closures during bottle fermentation of MCC?.................. 52 Steering away from flat and flabby Merlot . ............................................. 54 Effect of cork or crown cap closures on MCC bubbles . ........................... 57 Yeasts, smoke taint and Chenin blanc wines . .......................................... 59 The role of thiamine in sluggish fermentations and crushed dreams. ..... 62 Adding freshness back to wine with Level 2 Laktia™............................... 64

Reducing bentonite usage with a novel method to obtain heat-stable wines . ................................................................................... 68 Lipids in white winemaking – the too oft-ignored essential nutrients . ... 71 PRACTICAL IN THE VINEYARD . ......................... 74 Soil preparation – think before you do.................................................... 75 uniWines Vineyards’ quality strategy for higher-yielding vineyards ....... 79 Gen-Z – 2021 cover crop demos ............................................................. 82 Let your terroir guide your farm planning............................................... 89 Mulching on berms................................................................................. 91 Sawing back of grapevines for retraining. ............................................... 94 The cold facts about managing vineyard frost......................................... 96 PRACTICAL IN THE CELLAR .................................. 98 Effective microbiological monitoring in wine cellars ............................... 99 The use of dried yeast without rehydration........................................... 100 The making of wines with low or no alcohol......................................... 101 The benefits of aeration during fermentation ........................................ 102 Winetech vine and wine innovation watch: The use of fumaric acid to control malolactic fermentation................... 105 Actions in cork factories to prevent TCA in closures............................. 107 Calcium tartrate instability of wine. ...................................................... 108 Winetech vine and wine innovation watch: Treatment of grapes, musts and wine with pulsed electric fields . ......... 109 The complexities of sulphur dioxide...................................................... 111 Carbonic maceration............................................................................. 113 Modern amphorae and oak barrels. ...................................................... 114 Free sulphur dioxide management in barrels........................................ 115 Hot vineyards not that “VA VA” Voom after all...................................... 116 GENERAL ................................................................................. 118 Confronting Climate Change: Carbon emissions and the future of South African agriculture.............. 119 Carbon jargon – your quick guide to carbon literacy. ........................... 121 Confronting Cimage Change: Benchmark Report 2022........................ 122

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CONTENTS

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Anna Mouton Private consultant anna@annamouton.com

Erna Blancquaert South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University ewitbooi@sun.ac.za Francois Halleen ARC Infruitec-Nietvoorbij, Stellenbosch halleenf@arc.agric.za

Kyle Loggenberg Department of Geography and Environmental Studies, Stellenbosch University kyleloggenberg@sun.ac.za

Anél Blignaut Blue North Sustainability (Pty) Ltd, Stellenbosch anel@bluenorth.co.za Benoit Divol South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University divol@sun.ac.za

Lucinda Heyns Winetech, Paarl lucinda@winetech.co.za Manuela Campa Department of Genetics, Stellenbosch University mcampa@sun.ac.za

Gerhard Pietersen Pathsol, Wellington gerhard@pathsol.co.za Hanno van Schalkwyk Vinpro, Paarl hanno@vinpro.co.za

Marianne McKay South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University marianne@sun.ac.za Neil Jolly ARC Infruitec-Nietvoorbij, Stellenbosch jollyn@arc.agric.za

Bernard Mocke Laffort, Paarl bernard.mocke@laffort.com Carien Coetzee Basic Wine, Stellenbosch carien@basicwine.co.za

Harrison Davies Winetitles Media, Australia

Heinrich du Plessis ARC Infruitec-Nietvoorbij, Stellenbosch dplessishe@arc.agric.za Heinrich Schloms Vinpro, Paarl heinrich@vinpro.co.za Hennie Visser Vinpro, Robertson henniev@vinpro.co.za Johan de Jager Vinpro, Paarl johan@vinpro.co.za Karien O’Kennedy Winetech, Paarl karien@winetech.co.za

Charl Theron Private consultant vinofino@mweb.co.za Elize Jooste PPRI, Pretoria joostee@arc.agric.za

Pierre Snyman Vinpro, Worcester pierre@vinpro.co.za

Piet Loubser Lallemand SA ploubser@lallemand.com Rinus Knoetze ARC Infruitec-Nietvoorbij, Stellenbosch knoetzer@arc.agric.za Tarryn Wettergreen SATI, Paarl tarryn@satgi.co.za

Elleunorah Allsopp ARC Infruitec-Nietvoorbij, Stellenbosch allsoppe@arc.agric.za

Emma Carkeek Vinpro, Paarl emma@vinpro.co.za

AUTHORS

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One of Winetech’s key focus areas is the communication of research results, Winetech funded and international, to the South African wine industry. Using various knowledge transfer platforms, we aim to provide the industry with ideas for innovation that can contribute to the industry's sustainability in the long run. One of our technical resources is Winetech Technical, published monthly in WineLand magazine. The Winetech Technical Yearbook combines all the magazine articles published in a calendar year in one book for your convenience. In 2022 we published 50 articles related to grape growing and winemaking in WineLand magazine, covering topics such as Petri disease, leafroll disease, CRISPR, wine sparging, bio-control yeasts, MCC closures and many more. For our wine industry to remain competitive and profitable, constant innovation is vital. We sincerely hope the Winetech Technical articles contribute to greater awareness of innovative possibilities.

KIND REGARDS THE WINETECH TEAM

FOREWORD

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SHUTTERSTOCK

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SHUTTERSTOCK

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VITICULTURE

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JANUARY/FEBRUARY

Petri disease – WHEN AND HOW DO WESTERN CAPE VINEYARDS GET INFECTED?

RESULTS AND DISCUSSION During the study Pm. minimum perithecia and Pa. chlamydospora pycnidia were found on trunks and cordons of vines in several vineyards, as well as the “heads” of mother vines in rootstock mother blocks (Baloyi et al ., 2013, 2016). Perithecia were found in wood crevices and old pruning wounds, while pycnidia were found in crevices and cracks, as well as on bark and old pruning wounds. The spore trapping studies , which were conduct - ed from mid-March to the beginning of December over two seasons, revealed for the first time the presence of ae rial spores associated with Petri disease in South Africa (Hal leen et al ., 2020). Phaeomoniella chlamydospora and a total of 14 Phaeoacremonium species were identified, including Pm. australiense , Pm. griseo-olivaceum , Pm. griseorubrum , Pm. inflatipes , Pm. iranianum , Pm. italicum , Pm. minimum , Pm. parasiticum , Pm. prunicola , Pm. scolyti , Pm. sicilianum , Pm. subulatum , Pm. venezuelense and Pm. viticola. Of these, only Pa. chlamydospora, Pm. minimum and Pm. inflatipes have been reported as aerial inoculum within vineyards in other countries. This is by far the greatest diversity in Petri disease pathogens ever recorded in vineyards worldwide. The highest number of pathogen species found in a single vineyard was eight and six in a rootstock mother block. Two pathogen species, Pa. chlamydospora and Pm. minimum , were trapped in all the vineyards and rootstock mother vine nurseries during both seasons of the study. One of these two pathogens was the predominant species detected in all vineyards, except in Rawsonville where Pm. sicilianum was the predominant species. Similar to previous isolation studies conducted in South Africa, Pm. parasiticum appears to be the most common Phaeoac remonium species associated with grapevine after Pm. minimum , as this species was detected in four and six vineyards, respectively, during the two spore trapping seasons. Petri disease pathogens were detected throughout the trapping periods in all the vineyards. Spore release coincided with winter and spring (i.e. suckering) pruning activities. Phaeomoniella chlam ydospora and/or Pm. minimum spore release events occurred during the week of pruning or within four weeks after pruning, and rootstock cane harvesting in all the vineyards and rootstock mother blocks. Grapevine pruning wounds remain susceptible to Petri disease pathogens for four to sixteen weeks after pruning. Phaeoacremonium sicilianum and Pm. parasiticum spores were also detected after pruning in Rawsonville and one vineyard in Paarl, respectively, in both seasons. Phaeoacremonium subulatum , Pm. scolyti (Rawsonvile), Pm. prunicola (Stellenbosch), Pm. irani anum (Paarl) and Pm. inflatipes (Durbanville) were also detected during the susceptible period, but during only one of the seasons

THE AIM OF THE CURRENT STUDY WAS TO IDENTIFY PETRI DISEASE PATHOGEN INOCULUM SOURCES IN VINEYARDS AND ROOTSTOCK MOTHER BLOCKS AND TO DETERMINE IF, AND WHEN, SPORES ARE RELEASED AND WHETHER SPORE RELEASE EVENTS COINCIDE WITH SUSCEPTIBLE PERIODS IN VINEYARDS AND MOTHER BLOCKS.

BY FRANCOIS HALLEEN, ANNABELLA BALOYI & LIZEL MOSTERT

INTRODUCTION Petri disease is a serious problem in grapevines affecting grape production worldwide including South Africa. The disease is caused by xylem inhabiting fungi Phaeomoniella ( Pa. ) chlamydospora , Phaeoacremonium ( Pm. ) minimum and several Phaeoacremonium species and usually affects young vines in newly established vineyards. Symptoms include stunted growth, shortened internodes and dieback. Internal symptoms include black to brown spots (in cross-sections) and brown streaking in the xylem tissues (in lengthwise cuts). Petri disease pathogens spread within vineyards as aerial inoculum, which originates from fruiting bodies. Pruning wounds are known host ports of entry for aerial spores of these pathogens. However, knowledge is lacking on the occurrence of these fruiting structures within South African vineyards, as well as its possible contribution towards aerial inoculum. At the onset of the current project, only limited information was available from studies conducted in Grapevine wood pieces were investigated for fruiting bodies. Spore trapping studies were conducted in six 24 - 40 year-old vineyards (two each in Stellenbosch and Paarl, and one each in Rawsonville and Durbanville) and two rootstock mother blocks (19 year-old in Slanghoek and 17 year-old in Wellington) over two seasons. Pathogenicity studies with newly found Phaeoacremonium spp., or species that have not been subjected to pathogenicity studies in local vineyards, were conducted on field-grown Cabernet Sauvignon vines by inoculating pruning wounds. France, California and Australia. MATERIALS AND METHODS

Black vascu lar streaking

associated with Phaeomoniella chlamydospora wound infection in a grapevine rootstock (left). In a cross-section, the occluded xylem vessels can be seen as black spots (right).

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and only in specific vineyards. Phaeoacremonium scolyti was also detected during this period in the Slanghoek rootstock nursery. No correlation could be found between spore release and specific weather conditions (i.e. rain fall), and therefore farmers must be aware that spores are also released during dry periods. Previous studies conducted in the same Rawsonville and Stellenbosch vineyards identified numerous arthropod species carry ing Petri disease pathogen spores that could vector these to neighbouring plants (Moyo et al ., 2014). The practice of establishing new vineyards in close proximity to old vineyards may lead to early infection during wounding and faster disease development in young vines as spores are aerially dispersed. In the current study, spore traps were also placed in newly established vineyards adjacent to the 24 year-old vineyard in Rawsonville and 30 year-old vineyard in Paarl. In these vineyards, pathogens detect ed in the old vineyards were also trapped in the young vineyards, including Pa. chlamydospora , Pm. minimum , Pm. sicilianum and other trunk disease pathogens. Many Phaeoacremonium species also have wide host ranges, many of which are planted in close proximity to vineyards, and these act as additional inoculum sources (Spies et al ., 2018). This emphasises the need to adopt wound protec tion and control strategies as early as possible. The patho genicity trial conducted with nine Phaeoacremonium spe cies found in South African vineyards for the first time on pruning wounds showed that all the Phaeoacremonium species were pathogenic (Baloyi et al ., 2018). This is also in line with a previous study where Phaeoacremonium species were shown to be pathogenic when inoculated on grapevine trunks and pruning wounds (Halleen et al ., 2007). CONCLUSION Fruiting bodies of Petri disease pathogens were found in several vineyards, as well as rootstock mother blocks in the Western Cape. Spore trapping studies showed that spores are released throughout the year. The high species diversity and frequency of spore release in vine yards and rootstock mother vine nurseries coinciding with traditional pruning practices emphasise the need to develop effective wound protection strategies to avoid in fection of unprotected pruning wounds. The occurrence of Pa. chlamydospora and six Phaeoacremonium species in rootstock mother vine nurseries, highlights the risk of pathogen spread through infected nursery material. Pruning wound protection in rootstock mother blocks and sanitation practices during the propagation process are therefore highly recommended together with similar practices in vineyards. ABSTRACT Petri disease, caused by Phaeomoniella chlamydospo ra and Phaeoacremonium species, is one of the major grapevine trunk diseases affecting young vines in newly established vineyards. Prior to this study, no information was available on the availability of inoculum within South African vineyards and rootstock mother blocks. Not only was viable inoculum sources found within vineyards and rootstock mother blocks, but a positive correlation was found between spore release and susceptibility periods during pruning and suckering activities when spores infect wounds. These results highlight the importance of sanitation practices in nurseries and vineyards, as well as the necessity to protect wounds. ACKNOWLEDGEMENTS AND REFERENCES https://www.wineland.co.za/petri-disease-when-and how-do-western-cape-vineyards-get-infected/

Example of an artificially inoculated Cabernet Sauvignon pruning wound several months after being inoculated with a Pheoacremonium spore suspension. Notice the brown to black streaking in the xylem originating from the wound.

Phaeomoniella chlamydospora fruiting bodies (pycnidia) forming in aggregates on grapevine bark (left). A closer view of the globose fruiting bodies (right).

Phaeoacremonium flask-shaped fruiting bodies (perithecia) with long necks. The fruiting bodies are sometimes hidden in deep cracks and crevices and therefore produce long necks to release their spores (left). The spores are released in sticky droplets that form at the neck opening on the tip (right). This is also an adaptation for arthropods to pick up spores and to vector these pathogens to new hosts.

Vaseline-coated microscope slide spore traps affixed to arms of infected vines (left) and visually healthy rootstock mother vines (right). The slides were replaced weekly and fungal spores were retrieved from them, cultured, counted and identified. No tice all the old pruning wounds with cracks and crevices. These are typical hiding placed for fungal fruiting bodies that produce and release spores into the air to infect nearby plants.

For more information, contact Francois Halleen at halleenf@arc.agric.za.

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MARCH

SHUTTERSTOCK

Smokin’ hot Western Cape terroir (PART 1)

THIS ARTICLE CONTAINS SCIENTIFIC FACTS, AS WELL AS THE RESEARCHER’S OWN PERSONAL OPINION, ABOUT INTERNAL AND EXTERNAL FACTORS IN TERROIR EXPRESSION.

BY MARIANNE MCKAY E evoked Australian vineyards baking in the afternoon sun, with kookaburras (very original, I know) calling in the hot gum trees nearby. Australian red wine is known for a minty green attribute that may present anywhere on the spectrum from full-on crushed gum-leaf to subtle garden spearmint. 1 The compound responsible for the minty/eucalyptus flavour in the Jacob’s Creek is 1,8-cineole, (commonly known as eucalyptol). Higher concentrations in wine are related to the presence of eucalyptus trees growing near the grapevines. For me, this is a powerful expression of terroir. METHOXYPYRAZINES AND TERPENES The terroir concept is complex and encompasses a huge number of factors including the grapevine’s own responses to climate, water, canopy management practices and soil composition. The methoxypyrazine concentrations found

in grape berries are a good example of an endogenous (internal) grapevine response to environmental conditions around it. Australian researchers have been able to differentiate international terroir/origin of wines based on their 3-isobutyl-2 methoxypyrazine (IBMP: ‘green pepper’ aroma) concentrations. Bordeaux wines were shown to have significantly lower levels of IBMP than their Australian counterparts. Climate, grape maturity, light exposure, various viticultural management practices and crop yield can all affect IBMP concentration, so it makes sense that the terroir will have a huge influence on these compounds. Another set of compounds that reflect grapevine’s endogenous responses are terpenes (spicy, floral smelling compounds in Muscat and Riesling grapes). It is well known that terpene concentrations increase in these cultivars in response to sunlight exposure and higher temperatures.

EUCALYPTUS AND TERROIR I tasted a Jacob’s Creek 2006 Cabernet Sauvignon the other day, definitely a rare occurrence for me. Despite the wine being 15 years old, the eucalyptus note leapt enthusiastically out of the glass and

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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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The other wines, despite the grapes hav ing been exposed to smoke, and having higher volatile phenol levels, were not over whelmingly smoky, and showed attributes which included ‘berries’, ‘floral/ violets’, ‘prunes/raisins’, ‘vanilla/caramel’, ‘tobacco’ and ‘pencil shavings’. High fruit intensity seemed to mask any sensory contribu tion by the VPs present in these wines, as has been indicated by previous work. Our own South African research 7 showed that guaiacol could contribute ‘sweet, woody’ notes to wine and French workers 8 found that VPs could enhance red wine esters (‘sweet, fruity’ notes). In fact, in the wines we investigated, guaiacol (even at higher levels) did not seem to be correlated with a perception of ‘smoke’ in any of the wines unless it was in combination with oth er phenols. 9 Oakwood also contributes a range of volatile phenols including guaiacol, 4-methyl guaiacol, the furfurals and euge nol, and nobody complains too much about the olfactory impacts of those. In fact, the judicious use of a bit of wood might work to help mask some of the VPs by adding sweet, Coming back to my point about chemical composition. So, what if the grapes have been exposed to smoke? It’s not always the case that the wine is an ashy mess, even if the smokiness is there. In fact, it may be that a combination of the ‘subtle, herbal’ notes imparted by fynbos , along with a little smokiness may give our red wines an un mistakable identity in a highly competitive market. It might be argued that a wine con taining some smokiness is more accurately reflecting the landscape of its origin than one that has been stripped of these vintage and terroir effects. Why are we trying to pretend that our indigenous, ecologically necessary fires never happen? The olfac tory space in a red wine is complex, and if grapes have been exposed to smoke, they don’t necessarily need to be written off or banished to an entry-level blend. And it’s not only me that is thinking this way… See Part 2 for the emerging thinking around smoke ‘taint’ in wine. ABSTRACT Discussing the exogenous or external factors that form part of world-famous wine terroir in Part 1, this opinion piece lays out the rationale for well-managed volatile phenols derived from inevitable wildfire events to form a part of our own Western Cape terroir expression. Part 2 shares some insights into consumer reactions to smoke events around the world, demonstrating that wine lovers are not always predictable in their reactions, and quality is in the mind (and on the palate) of the beholder. coconut and spice flavours. TAINT? WHAT TAINT?

FIGURE 2. Olfactory effects of volatile phenols in red wine.

to this that VPs are persistent little beggars that can’t easily be removed or chemically reacted away. This was underlined yet again in a recent comprehensive review of mitigating factors for smoke taint. “Although the issue has prompted a surge in research on the subject in recent years, no singular solution has yet been identified that is capable of maintaining the quality of wine made from smoke affected grapes.” 6 Thus, one is yet again made aware of how much we know as a global industry about smoke taint (the ‘what’ and the ‘why’ are very well covered, specifically by the Australians), but the ‘what now’ seems to have been left out in the cold. Isn’t it time ”THE SUBTLE, HERBAL NOTES IMPARTED BY FYNBOS ALONG WITH DISCREET SMOKINESS MAY GIVE OUR WESTERN CAPE RED WINES A HIGHLY DESIRABLE EDGE IN A COMPETITIVE MARKET.”

we cut our winemaking industry a little slack and took a slightly different view of this issue? WHAT HAVE WE FOUND OUT ABOUT OUR OWN BACKYARD BRAAI? We have been working on this issue consistently at the Department of Viticulture and Oenology, since around 2012 when we graduated our first Master’s student specialising in volatile phenol effects on wine. Since then, at least five Master’s and one PhD have beavered away looking at how we can work with what we have, helping our industry to solve the problem as pragmatically as possible. For example, during 2018, 12 wines were submitted to the Department of Viticulture and Oenology by South African wine industry members concerned that the wines might be smoke tainted. These wines were from regions that had experienced fire events prior to harvest, some bad, some not so bad. The wines were screened for a broad range of VPs, and the results were published in SAJEV. Historical data concerning fire events in the regions from which the wines originated, and during the relevant vintages were also investigated. The wines were evaluated by our “smoke expert” sensory panel and analysed chemically for VPs. The wines contained a wide range of VPs in different concentrations. On the sensory side, out of 12 wines, four were described with negative attributes (‘smoky’, ‘ashy’ and ‘burnt rubber’), at significantly higher levels than the others.

REFERENCES https://www.wineland.co.za/smokin-hot-western-cape-terroir-science-behind/

For more information, contact Marianne McKay at marianne@sun.ac.za.

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APRIL

Smokin’ hot Western Cape terroir (PART 2)

SHUTTERSTOCK

12 E ECONOMIC IMPACT OF SMOKE EVENTS The economic impact of smoke events near vineyards on producers can be devastating. Our research into the Elgin fire of 2017 indicated that an economic loss of around R5-million was incurred by the farmers we spoke to, with some abandoning their top/flagship ranges. Similarly fires in the Hemel-en-Aarde Valley in 2019 burned vineyards and had massive impacts on the winemaking community. If we go back slightly further, the 2015 fire that savaged the Peninsula also impacted producers in the region severely. And these are just the big events. At some point each decade (or even more frequently), every Western Cape vineyard will likely be exposed to a range of smoke-associated volatile phenols (VPs), which may then transfer to wine. 1 Do we expect producers to write off their entire harvest, and be more financially ex BY MARIANNE MCKAY WINETECH TECHNICAL YEARBOOK 2022

THIS ARTICLE CONTAINS SCIENTIFIC FACTS, AS WELL AS THE RESEARCHER’S OWN PERSONAL OPINION, ABOUT THE EMERGING THINKING AROUND SMOKE ‘TAINT’ IN WINE.

posed than they already might be in these extremely tough economic conditions? Let’s consider what happened in Australia and Oregon. CONSUMER REACTION TO SMOKY WINE: THE BURNING ISSUE As most people know, Australia was hit by devastating wildfires in 2019/20. Bush fires in Australia, just as in the Western Cape, are a widespread and regular oc currence, but the 2019/20 fire season was devastating for people, animals and the wine industry. M. Allen 2 explored this is sue with Australian winemakers and found that a number of them had decided to be upfront about the smoke issue with their customers, recommending that the wines were not kept, but consumed as quickly as possible. Surprisingly, the smoke-affected wines sold well, some even at premium prices. Previously, even a hint of smoke taint had been seen as completely off-put

ting for consumers, but it seemed that there was an unexpected emotional as pect involved. The devastation caused by the 2019/20 fire season, and its massive impact on the industry, had led to some ‘philanthropic support’ amongst consum ers. The combination of drought and fire on the Australian wine industry had made consumers realise they needed to help or see a lot of small producers go under. So, they bought the wine, and they drank it. One winery owner in Allen’s article not ed that there is far too much of a fuss made about smoke taint, and that it “isn’t as much of an issue for wine consumers as winemakers think it is”. Customers saw the smoky character as a feature of the wine, not a fault, and were happy to try something different. Allen suggests that this may be an indication that the market is maturing, and able to have ‘nuanced discussion’ instead of simply writing the entire vintage off. In Oregon, hit by devastating fires in 2020, opinions amongst consumers also seemed to shift. As many as 70% of Or egon producers make fewer than 5 000 cases of wine a year, 3 so these small op erations cannot afford to spend a whole year without production. Thus, despite the pall of smoke over winemaking areas, producers went ahead and made wine. Various strategies were employed (min imal pressing, wood treatment and rosé production instead of red), but the author notes that consumers are not so quick to call all smokiness in wine ‘taint’. Predicting very negative consumer reac tions to smokiness in some vintages may not actually be accurate. Much more re search is needed on consumer acceptance and rejection thresholds for smoke taint compounds. Certainly, Australian cus tomers appear to be thinking about smoke in wine differently now to how they once did. Perhaps it’s time for South Africans to follow suit? SO WHAT? The effect of vintage and terroir on a wine is not something anyone argues about. We all know it exists, and often, it overrides everything else (very frustrating if you are a viticultural researcher). Vintage effect embraces a whole range of factors from microclimate, flora, fauna, vineyard management and even the vineyard microbiome. Like S. Cole-Johnson, 3 and some of the Oregon and Australian winemakers, I too think of smoke as a part of the vintage and the Western Cape (in our case) terroir. What you are tasting

in your glass is an event that happened in a particular place at a specific time. Obviously not everyone will feel the same about a wine with hints of smoke, and it will be up to the individual winemaker or winemaking team what is done with a smoke-affected vintage based on their knowledge of their customers and their cultivars. EUCALYPTOL AND VOLATILE PHENOLS Coming back to the issue of a chemical and sensory flavour profile as an expression of terroir. D. Capone 4 and co-workers in Australia identified a few of the chemi cal markers in Cabernet Sauvignon that highlighted the role of various factors in defining regional typicity. Not all these markers are internal responses of grape metabolism to the environment, some are external, like eucalyptol and the volatile phenols. I loved the olfactory experience I had with the Jacob’s Creek wine, and appar ently, I am not alone. The presence of eucalyptol isn’t off-putting to consumers. Capone 4 also showed that Australian con sumers actually preferred wines that had been spiked with low levels of eucalyptol compared to clean controls. It has been suggested that tasters from other coun tries are more likely to pick up the green notes in Australian wine, as the locals have become de-sensitised to it, and thus Australian winemakers are divided over whether it’s desirable. I’m going to side with those who say that it is. Obviously, an overwhelming eucalyptus attribute, which dominates the wine to the detriment of everything else would be unacceptable, but a subtle eucalyptus, minty note that is there as a direct result of grapes being grown in the Australian landscape does not seem to pose a big problem for the average consumer. REVISITING SMOKINESS Likewise with volatile phenols and smoki ness. A greater understanding of the chem istry behind terroir expression (including adverse events of any kind impacting the landscape) will provide producers with knowledge that can be used for promot ing their wines and enhancing sales. A greater understanding of how and why consumers make choices, and what their acceptance and rejection thresholds are for smoke taint-related compounds like RETURNING TO THE COONAWARRA CAB

volatile phenols will also help winemakers to make decisions around production and amelioration strategies. FINAL THOUGHTS A decade and a half had passed since those grapes had ripened in an Australian vineyard, and I was transported back to that time and place by the evocative aroma of gum trees. This is, of course, the magic of wine. Not only is it a time capsule, but it is also a place capsule. What other product can claim that so effectively? The sunshine, the wind and even the people who worked the land and the wine are somehow trapped in the bottle. A little greenness does nothing to dissuade the average international consumer from loving an Australian Cab. Why then are we so determined to deny the fact of our landscape, our terroir? Why should we Western-Capers not trap a little carefully curated fynbos- smoke in the bottle occasionally, to transport others back to a different time and place? It is, after all, our history trapped in a bottle. ABSTRACT Discussing the exogenous or external fac tors that form part of world-famous wine terroir in Part 1, this opinion piece lays out the rationale for well-managed volatile phenols derived from inevitable wildfire events to form a part of our own Western Cape terroir expression. Part 2 shares some insights into consumer reactions to smoke events around the world, demon strating that wine lovers are not always predictable in their reactions, and quality is in the mind (and on the palate) of the beholder. REFERENCES https://www.wineland.co.za/smokin hot-western-cape-terroir-part-2/

For more information, contact Marianne McKay at marianne@sun.ac.za.

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APRIL

Impact of grapevine leafroll disease on grape and wine composition GRAPEVINE LEAFROLL DISEASE (GLD) IS THE MOST COMMON GRAPEVINE DISEASE, WHICH IS PRESENT IN GRAPE-GROWING REGIONS GLOBALLY. IT HAS BEEN PROVEN THAT GLD IMPACTS GRAPEVINE PHYSIOLOGY AND THE SUBSEQUENT BERRY COMPOSITION. VERY LITTLE INFORMATION IS AVAILABLE ON GLD IMPACT ON GRAPEVINE PHYSIOLOGY, GRAPE RIPENING AND THE WINE COMPOSITION UNDER SOUTH AFRICAN CONDITIONS.

I

BY ERNA BLANCQUAERT & WESSEL DU TOIT

INTRODUCTION To date 70 viruses and five viroids have been identified to infect grapevines. 1 Vi rus and virus-like diseases are a great threat to grapevine vineyards globally. 1 Grapevine leafroll disease (GLD) has been identified as one of the most important viral diseases. 2 Within the South Afri can context, grapevine leafroll disease is widely accepted to be the most damaging grapevine virus disease, with grapevine leafroll-associated virus 3 (GLRaV-3), the most prevalent leafroll-associated virus. 3,4 This virus is transmitted by vine

mealybug Planococcus ficus which is the predominant mealybug in South African vineyards, as well as the more restricted Pseudococcus longispinus and a number of scale insect species. 5,6 The spread of a systemic virus such as GLRaV-3 is influenced by the direction of the carbohydrate movement in the phlo em. 7 The sieve elements are blocked and ruptured in the parenchyma cells in the leaves which will result in a delay of the carbohydrate translocation. 8 Subsequently, carbohydrates cannot be mobilised and transported further from the leaves to oth er grapevine organs which subsequently

HANNO VAN SCHALKWYK

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WINETECH TECHNICAL YEARBOOK 2022

TABLE 1. Vineyard measurements and harvest data obtained in 2017/2018.

Stomatal conductance (mmol m-² s-¹)#

Main shoot length (cm)*

Lateral shoot length (cm)*

Berry weight – 50 berries (g)^

Bunch numbers^

Bunch weights^

Vineyard Treatment

AS

106.58 ± 31.34 a 57.98 ± 29.45 a 2.08 ± 1.07 a 61.70 ± 1.84 b 19.17 ± 6.34

1.82 ± 0.59

Cabernet Sauvignon A

SV

51.00 ± 31.53 b 9.14 ± 6.19 b 1.52 ± 1.50 b 71.68 ± 2.33 ab 20.10 ± 10.20

1.86 ± 1.31

SVLH

73.54 ± 3.70 a 19.40 ± 8.70

1.61 ± 0.80

AS

93.10 ± 22.94 48.78 ± 23.65

2.63 ± 1.44

75.03 ± 2.91 32.13 ± 20.38

3.04 ± 2.30

Cabernet Sauvignon B

SV

63.64 ± 18.81 35.06 ± 43.04

2.20 ± 1.91

64.98 ± 8.28 34.40 ± 14.05

3.44 ± 1.70

SVLH

72.31 ± 2.87 38.35 ± 14.55

3.49 ± 1.54

AS

91.12 ± 18.27 a 47.34 ± 25.12 a 3.12 ± 2.08 a 94.50 ± 4.60 a 21.25 ± 4.85 4.57 ± 1.80 a

Merlot noir

SV

60.84 ± 11.62 b 10.34 ± 13.04 b 1.07 ± 0.76 b 62.44 ± 3.48 c

25.40 ± 8.32 3.68 ± 1.45 b

SVLH

81.10 ± 1.68 b 25.95 ± 15.05 2.98 ± 1.78 b

Cabernet Sauvignon A Cabernet Sauvignon B

*

**

***

*

ns

ns

p-value

ns

ns

ns

ns

ns

ns

Merlot

*

*

***

***

ns

**

*- Mean values n=5 determined at pea-size; # - Mean value, n=3 determined on three days throughout the season; ^ - Mean value, n=20 grapevines determined at harvest.

TABLE 2. Grape juice analysis at harvest.

2016/2017

Vineyard

Treatment

Brix

pH

TA

AS

24.9 ± 0.73 a

3.66 ± 0.11 a

6.8 ± 0.24 b

Cabernet Sauvignon A

SV

22.7 ± 0.37 b

3.44 ± 0.04 b

7.66 ± 0.03 a

SVLH

23.5 ± 0.25 b

3.37 ± 0.04 b

7.10 ± 0.34 b

AS

26.3 ± 0.37 a

3.47 ± 0.04 a

7.07 ± 0.15 b

Cabernet Sauvignon B

SV

22.5 ± 0.60 c

3.34 ± 0.01 b

8.28 ± 0.15 a

SVLH

24 ± 0 b

3.38 ± 0.04 b

6.76 ± 0.13 b

Cabernet Sauvignon A

**

**

*

p-value

Cabernet Sauvignon B

***

**

***

2017/2018

Vineyard

Treatment

Brix

pH

TA

AS

25.40 ± 0.36 a

3.64 ± 0.01 a

6.02 ± 0.19

Cabernet Sauvignon A

SV

22.80 ± 0.80 b

3.39 ± 0.06 b

6.37 ± 0.51

SVLH

25.45 ± 0.35 a

3.39 ± 0.02 b

6.57 ± 0.14

AS

23.67 ± 0.51 a

3.36 ± 0.02 a

6.19 ± 0.17 b

Cabernet Sauvignon B

SV

21.13 ± 0.23 b

3.20 ± 0.01 b

7.14 ± 0.11 a

SVLH

23.35 ± 0.35 a

3.27 ± 0.01 c

6.73 ± 0.12 c

AS

23.70 ± 0.10 a

3.58 ± 0.01

5.87 ± 0.13

Merlot noir

SV

22.20 ± 0.17 c

3.41 ± 0.06

6.12 ± 1.73

SVLH

23.05 ± 0.45 b

3.62 ±0.03

6.07 ± 0.12

Cabernet Sauvignon A

**

***

ns

p-value

Cabernet Sauvignon B

***

***

***

Merlot

**

ns

ns

ANOVA was used to compare data. Asymptomatic vine – AV; Symptomatic vines – SV; and Symptomatic vine late harvest – SVLH. Mean followed by significant letters in a row are significant at p<0.05 (Fischers LSD). The standard deviation of three replicates per treatment were determined. Significance of one-way ANOVA for virus presence on the grape parameters. Significance (*, ** and *** indicate significance at p≤0.05, 0.01 and 0.001 respectively; ns: not significant).

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WINETECH TECHNICAL YEARBOOK 2022

TABLE 3. Wine chemical analysis in the study.

Vineyard

Treatment

pH

TA

Ethanol

2016/2017

AS

3.74 ± 0.12 a

6.26 ± 0.36 b

14.93 ± 0.15 a

Cabernet Sauvignon A

SV

3.52 ± 0.04 b

7.03 ± 0.05 a

13.54 ± 0.21 b

SVLH

3.61± 0.08 b

6.71 ± 0.17 ab

13.10 ± 0.48 b

AS

3.63 ± 0.04 ab

6.8 ± 0.12 b

16.02 ± 0.20 a

Cabernet Sauvignon B

SV

3.66 ± 0.02 a

6.24 ± 0.20 c

13.00 ± 0.60 b

SVLH

3.45 ± 0.15 b

8.24 ± 0.34 a

13.97 ± 0.35 c

Cabernet Sauvignon A

*

*

**

p-value

Cabernet Sauvignon B

*

***

***

2017/2018

AS

3.56 ± 0.21

5.67 ± 0.29 b

13.78 ± 1.14

Cabernet Sauvignon A

SV

3.40 ± 0.062

6.08 ± 0.07 a

13.64 ± 0.40

SVLH

3.54 ± 0.05

6.27 ± 0.06 a

14.49 ± 0.27

AS

3.43 ± 0.01 a

5.93 ± 0.11

14.21 ± 0.24 a

Cabernet Sauvignon B

SV

3.32 ± 0.02 b

6.02 ± 0.08

12.28 ± 0.28 c

SVLH

3.42 ± 0.01 a

5.93 ± 0.02

13.45 ± 0.27 b

Merlot noir

AS

3.56 ± 0.007 a

5.34 ± 0.07 a

14.11 ± 0.04 a

SV

3.48 ± 0.03 b

5.56 ± 0.10 b

12.78 ± 0.21 c

SVLH

3.51 ± 0.03 ab

5.46 ± 0.07 ab

13.35 ± 0.41 b

Cabernet Sauvignon A

ns

**

ns

p-value

Cabernet Sauvignon B

***

ns

***

Merlot noir

*

*

**

ANOVA was used to compare data. Asymptomatic vine – AV; Symptomatic vines – SV; and Symptomatic vine late harvest – SVLH. Mean followed by significant letters in a row are significant at p<0.05 (Fischers LSD). The standard deviation of three replicates per treatment was determined. Significance of one-way ANOVA for virus presence. Significance (*, ** and *** indicate significance at p≤0.05, 0.01 and 0.001 respectively; ns: not significant).

MATERIALS AND METHODS The study was conducted during the 2016/2017 and 2017/2018 growing seasons in two commercial Cabernet Sauvignon vineyards (hereinafter Cabernet Sauvignon A – clone CS 12/R110 and Cabernet Sauvignon B – clone CS 45/101 14 Mgt) with a north-south and east-west row orientation in the Stellenbosch wine region. In 2017/2018 a commercial Merlot noir vineyard (clone MO343/R99) in the Constantia wine region was also evaluated. Vineyards were visually evaluated for typical GLD symptoms. Thirty symptomatic (SV) and 30 non-symptomatic (AS) grapevines were selected in each vineyard. An additional 30 symptomatic vines were selected which were harvested two weeks later than the commercial harvest date (SVLH). The 2016/2017 season was aimed at identifying SV- and AS-infected grapevines in commercial vineyards through virus di agnosis. Grape berries were sampled at the commercial harvest date and subjected to

result in the downward rolling leaves and become brittle. 8 Red cultivars express red spotting which turn red purple colour and a green vein-banding symptom and inter veinal yellowing of leaves and leafrolling in white cultivars. 2,8 Previous studies on GLD in red grape varieties reported significant losses in both yield and fruit quality. 9-13 The wine proper ties were also impacted by the presence of GLD. Wines made from non-symptomatic vines were perceived as being more purple in colour, with less brown and with a more saturated colour. 11 The aim of this study was to: (i) evaluate the occurrence of GLD and non-GLD-infected grapevines in commercial vineyards, (ii) monitor GLD infection rate in a commercial vineyard over a two season period, (iii) grapevine physiological responses to GLD, and (iv) evaluate the impact of fruit and wine chemistry.

classical analysis, total soluble solids (TSS), pH and titratable acidity (TA). The bunch number and bunch weights were record ed. Wines were made from the harvested grapes according to the experimental cellar protocol from the Department of Viticulture and Oenology, Stellenbosch University. In 2017/2018 the same grapevines which were used in 2016/2017 were sub jected to virus diagnosis to ensure that the AS were not infected during the course of the season. Destructive shoot mea surements were performed at pea-size. Stomatal conductance was recorded and grape ripening was monitored throughout the season from véraison until commercial harvest and post commercial harvest for the SVLH treatment. The same harvesting and winemaking protocols followed in 2016/2017 were repeated 2017/2018. STATISTICAL ANALYSIS One-way and two-way analyses of vari ance (ANOVA) were performed on the grape chemical and wine chemical data

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WINETECH TECHNICAL YEARBOOK 2022