Unbottling the flavour of wine yeasts: an exploration of bubbling diversity

The production of wine from grapes is believed to date back to Neolithic times and most likely originated from the broader Anatolia region in contemporary Türkiye. Over millennia, this practice journeyed westwards along the shores of the Mediterranean Sea, ultimately reaching France around the sixth century BC. The last step of the expansion occurred during colonial times when European settlers planted vineyards in various countries and continents, starting with South Africa in the mid-1650s. Today, wine production represents a significant international industry that reached 258 million hectolitres in 2022 with global exports representing €37,6 billion, according to the International Organisation of Vine and Wine (Paris, France).

This long history is a testimony to the fascination that wine has exerted on people for over eight millennia. From the early beginnings of winemaking, particular attention has been given to finding the best terroirs. Viticultural and winemaking techniques were empirically optimised, and yet they barely changed until the 19th century. Moreover, the transformation of grape juice to wine through the process known as ‘alcoholic fermentation’ remained mysterious for the greater part of wine history, and wine did not always taste like today’s wine: it used to be generally weak in alcohol, colour and structure, and often displayed certain organoleptic characteristics that would today qualify it as faulty. The addition of herbs, spices, honey and so forth was common to prevent or hide sensory faults, but obviously altered the wines’ organoleptic profiles.

Financial crises linked to low revenue from spoilt wines as well as the advent of microbiology halted this state of scientific ignorance in the mid-19th century, when Louis Pasteur demonstrated that fermentation is a biochemical process driven by microscopic organisms, later identified as yeasts. He also successfully proposed heat as a treatment to remediate microbial spoilage. Pasteur’s discoveries truly unlocked the potential of wine as a beverage of incredible organoleptic complexity and diversity, allowing winemakers to control and manipulate the outcome of fermentation for the production of different wine styles, while preventing the development of spoilage microorganisms and ensuring the ageing and preservation of faultless, unadulterated wines.

Benefiting from 150 years of research in wine microbiology, the art of winemaking rapidly evolved, together with the flavour landscape, to create the quality that we enjoy today. But after so many decades of research, is there still something to discover in wine microbiology?

The short answer is obviously yes, owing to wine’s complexity, not only as a beverage but also as a chemical and microbiological matrix. Indeed, the organoleptic richness and diversity of wine arise from the intricacy of its chemical composition, which in turn originates from the composition of grapes, the winemaking process, the microorganisms involved in its production and chemical reactions occurring during ageing. While the composition of grapes and its diversity fall beyond the scope of this lecture, it is a critical aspect that cannot be ignored.

Unlike other fermented beverages, the raw material (e.g. grape juice) is not sterilised. Subsequently, a large variety of indigenous microorganisms are involved in the fermentation process, especially in its early stages. Furthermore, the yeast Saccharomyces cerevisiae typically outcompetes the other yeast species. Following the early work of Pasteur and until the late 20th century, these other yeast species were often regarded as associated with problem fermentations and spoilage, and wine microbiologists typically refer to them collectively as non-Saccharomyces yeasts. For decades, research focused on S. cerevisiae, its nutritional requirements, its production of flavour compounds and the selection of strains of interest for their inoculation into grape juice. Indeed, advances in the field of microbiology, molecular biology and systems biology allowed, and still allow, the isolation and generation of a large diversity of strains that are now commercially available. Nevertheless, while S. cerevisiae has not yet revealed all its secrets, the past two decades have seen renewed interest in these so-called non-Saccharomyces yeasts. This is driven by the continuous search for (1) even more organoleptic diversity as a result of a change of drinking habits and tastes in wine consumers and (2) solutions to produce wine in a more sustainable (both financially and environmentally) and somewhat less interventionist way. And while the heterogeneity within the S. cerevisiae species continues to amaze us, non-Saccharomyces yeasts open a new basket of untapped diversity that requires further investigation. Moreover, because non-Saccharomyces yeasts cannot complete alcoholic fermentation under winemaking conditions, their involvement in wine fermentation only occurs in the context of interactions with other yeasts, which remain poorly understood, but create both challenges and opportunities to yield more diverse wines.

This lecture provides an overview of the speaker’s modest contributions to the field of wine microbiology over the past 20 years. It focuses mainly on the broader field of wine yeast biochemistry and specifically on the following themes: (1) yeast physiology (i.e., nutritional requirements and metabolism) and (2) yeast cell wall biochemistry and enzymology. The lecture concludes with an overview of the speaker’s envisaged future research outlooks to unleash the lurking oenological potential of various yeast species not only as aroma producers, but also as problem-solving bioagents.

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Short biography

Benoit Divol was born on 12 December 1977 in Paris, France and grew up in the town of Draveil, a mere 20 km southeast of the centre of Paris, in a family of teachers. He studied biology, agriculture and oenology, eventually leading him to research in the fascinating field of wine microbiology. After obtaining his PhD in 2004, he started working at Stellenbosch University, initially as a postdoctoral fellow (2005–2007) and then successively as a researcher (2007–2013), senior lecturer (2013–2017) and associate professor (2017–2021). During the latter period, he acted as head of the Department of Viticulture and Oenology (2017–2019). He was promoted to full professor in January 2022. He also obtained a Habilitation à Diriger les Recherches (DSc) in oenology from the University of Bordeaux, France in 2010.

As of 2023, Prof. Divol has co-authored 70 scientific peer-reviewed articles and presented several presentations and posters at conferences, among other research outputs. He is a contributing editor of Food Microbiology and an associate editor of OENO One and the South African Journal of Enology and Viticulture. Twenty-three master’s and 11 PhD students have so far graduated under his supervision or co-supervision. He is currently heading a research team comprising one postdoctoral fellow, three PhD students, five master’s students and two BSc (Hons) students.

Prof. Divol was awarded a Y1 (promising young researcher) rating from the National Research Foundation in 2010, which was upgraded to C2 (established researcher) in 2017 and C1 in 2022. In 2020, he was also awarded the title of Knight of the Order of Agricultural Merit by the French government for strengthening scientific collaboration between France and South Africa in the field of oenology.

When not working, Prof. Divol enjoys reading historical and detective fiction books and mining the French archives to reconstitute his family’s history. He loves cooking and listening to baroque music. He jogs and swims on a regular basis for sanity, but when given the opportunity, truly enjoys hiking and cross-country skiing.

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