YEAST: Micro-cosmos – Denizens of the Must

MI R SM S: DENIZENS F THE MUST

The first time Hervé Klebanowski peered into a foaming, fragrant, fermenting vat of wine must, he knew he’d found his career. Throughout his studies in chemistry at the University of Bordeaux, Hervé had never ceased to look at the periodic table in awe, seeing not an arcane code of letters and numbers but the building blocks of life.

After graduation, while his more pragmatic classmates headed off to the oil or pharmaceutical industries, Hervé applied for an internship at an oenological laboratory in Bordeaux’s Right Bank. “Soon after came my first contact with fermentation in a winery,” he recalls. “I’ll never forget the incredible aroma, this mix of CO2 and fermenting sugars, and that moment you open the vat and see it bubbling, moving, breathing, and you realise that it’s alive.”

Without them we would have no coffee, no chocolate, our bread would be unleavened, our cheeses would be flavourless, and ours would be a world without beer or wine. And after thousands of years of coexistence, we are still trying to unveil the secrets of these single-cell organisms that sublimate our food and drink.

A voyage into the world of fermentation, in the laboratory of Château Palmer, and the realms of masters of bread, beer and cheese…

Twenty-five years later, Hervé has made studying the origin of that life his profession, as the head of wine research and development for Château Palmer. There, he manages the winery’s state-of-the-art laboratory, which enables the estate rigorously to monitor every vintage, from grape to bottle, in microscopic detail. “Look at a drop of wine must through the microscope and you see these rounded forms, some perfectly circular and others oval in shape,” he says. “Those are the microorganisms responsible for fermentation – the magic of yeasts.”

Words by Jeffrey T. Iverson

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For thousands of years that magic was attributed thanks to yeasts. Even after yeasts die they continue to deities, from the Sumerian goddess Ninkasi to to influence the wine; as their cells break down they release the Aztecs’ Tēzcatzontēcatl, to Bacchus of Rome. Then, polysaccharides, magnifying the wine’s body.” in 1680, Anton van Leeuwenhoek caught the first glimpse To shine a light on these minuscule beings of great import, of these curious floating globules in drops of beer under today leading estates are taking microbiological analysis a microscope. But not until the nineteenth century did to a level far beyond Petri dishes and epifluorescence scientists imagine that the globules were unicellular microscopes. So it is at Château Palmer, when a week before organisms linked to fermentation. The German biologist harvest Hervé, assisted by the vignerons and the entire Theodor Schwann called them Zuckerpilz (sugar fungus), cellar team, starts work preparing a pied de cuve – and in 1838 his colleague Franz Meyen provided a fermentation-starter made from the endogenous yeasts their Latin name: Saccharomyces cerevisiae. Finally, in 1857, naturally present in the vineyard. Compared to simply France’s Louis Pasteur proved definitively in a series inoculating one’s grapes with a single commercial yeast of pioneering experiments that yeasts were the living catalyst culture, it’s an eminently more complex – though rewarding for transforming sugars into alcohol.

– undertaking. To begin with, grapes are collected from One hundred and sixty years later, our fascination with the estate’s best parcels and placed in several special minithese tiny members of the fungus kingdom has hardly vats. “When we crush and macerate the grapes to launch diminished. The entire genome of Saccharomyces cerevisiae the fermentation, a competition begins. Because there are has now been decoded, yet scientists are still unravelling lots of yeasts present on berries’ skins – Saccharomyces yeasts’ role in winemaking. “It’s not just alcohol; a wine’s cerevisiae are the best fermenters, but there are also yeasts aromas are also at play,” says Hervé. “In the grapes, there of the Candida, Pichia, Lachancea genera – they too will are aromatic precursors with no smell or taste, yet during contribute to the wine’s aromatic complexity. But some the fermentation they are released, becoming volatile, yeasts, like Brettanomyces, are problematic and cause off

Bread

Since the Neolithic age, all leavened bread has risen thanks to ubiquitous wild-yeast spores.

Yet thousands of years later, Pasteur’s discoveries changed everything.

The possibility of isolating yeast strains led to the commercial production of modern, fast-acting baker’s yeast, revolutionising the industry. Today, a new generation of bakers wants to slow it down again.

In 2016, Christoffer Hruskova, a Michelin-starred chef famous for his Nordic approach to British cuisine, left restaurants to found The Bread Factory in London Fields.

As he puts it, “It’s about going back, way back to the way bread is supposed to be.” His recipe? Rye flour, water and salt, period. He scorns commercial yeast, instead using a biga (a kind of sourdough starter made of rye flour and water, teeming with wild yeasts and lactic bacteria), and allowing his dough twenty hours

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to rise! Today his bread is praised as some of the best in London for its incredible depth of flavour and lactic tang.

Across the Channel, Thierry Delabre has enjoyed a similarly meteoric rise since his baking debut at France’s Omnivore food festival in 2015.

Today, Delabre supplies remarkable sourdough to Parisian restaurants such as L’Astrance, Chez Antoine and Lucas Carton. His secret?

A separate levain or sourdough starter for each heritage-wheat variety he uses (he has several living in his refrigerator)… and patience. “A slow fermentation changes everything,” he says. “The problem today is that bakeries are constantly pushed to increase productivity. But when you accelerate the process, your bread becomes less digestible and less flavourful. Only time allows levain to degrade the gluten, transform the sugars and create complex aromas.”

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aromas. So we analyse all the pieds de cuve to choose the one with the most desirable yeasts, which will then be used during harvest to launch every fermentation in the best of conditions.”

Hervé will draw on an array of powerful technologies, from a qPCR analyser (which rapidly assesses the quality and quantity of yeast strains such as Brettanomyces by amplifying a targeted DNA molecule) to a GC/MS/SPME system.

The latter is capable of identifying soil samples from the planet Mars, but here serves notably to probe wine for the presence of any undesirable molecules, such as volatile phenols that can mask the wine’s aromas.

“Ultimately, these tools all serve a common purpose: to help us better understand this diversity of microbial life, so that we can bring out the best that nature has to offer us.”

It’s a challenge that’s repeated vintage after vintage, an unending quest to create the finest wine possible by collaborating with the denizens of a nearly invisible world.

And so endures a primal partnership, as old as the dawn of agriculture. The botanist Nicholas P. Money"1 has even argued that yeasts shaped civilisation, providing humanity – notably via the pleasures of food and drink, which they brought us – the incentive to quit our nomadic lifestyle and settle in villages, surrounding ourselves with fields of barley and hills of vineyards. As Claude Lévi-Strauss put it,

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the invention of brewing marked humanity’s passage from “nature to culture”. In that sense, yeasts are humanity’s link between present and past, between modern life and our deeper nature; they are the ferment that awakens us to the circle of life."

1 Further

reading: The Rise of Yeast: How the Sugar Fungus Shaped Civilization,

by Nicholas P. Money (Oxford University Press, 2018).

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Beer

Cheese

Perfect bread is fundamentally about symbiotic relationships between microorganisms, such as the acid-tolerant, maltoseindifferent yeast Candida milleri and the acid-producing, maltose-dependent bacterium Lactobacillus sanfranciscensis, found in San Francisco’s famous sourdough. But such elegant examples of interdependence abound in one of bread’s greatest companions as well – cheese.

“Roquefort is something of a miracle,” laughs Delphine Carles, thirdgeneration cheesemaker in the village of Roquefort-sur-Soulzon in southern France. “It all begins with the legend.”

One day, a shepherd caring for his sheep in the hills forgot his lunch of rye bread and cheese curd in a cave (where he’d taken shelter with a beautiful shepherdess). Days later he stumbles upon his lunch again, but the bread has moulded, and deepgreen veins have marbled the curds.

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Hungry, he bravely tastes the mouldy cheese… and Roquefort is born.

Today at Maison Carles, one France’s smallest and most ardently traditionalist Roquefort producers, that miracle of the ultimate bold and buttery blue cheese is recreated daily. Loaves of rye bread placed inside their natural caves are rapidly consumed in the cool dampness by the famous blue-green mould known as Penicillium roqueforti.

Having been collected, the mould is sprinkled onto fresh cheese curds, which are pressed into wheels and placed back in the same caves, where they mature to perfection on oak shelves harbouring a multitude of helpful yeasts and bacteria. “When we talk about Roquefort’s typicité, its distinctive characteristics, we’re also talking about a diversity of microorganisms,” says Carles.

Cheese isn’t solely a product of lactic-acid bacteria: as in coffee and cocoa beans, where bacteria

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also play key roles in the fermentation, yeasts are essential to providing compounds that give each product its identity. As one 2019 Swiss study noted, “yeasts are recognised as having an indispensable impact on the development of cheese flavour and texture”. Some eighty-one strains have been isolated in Roquefort cheese, from lactose-fermenting yeasts that open up the curd texture, allowing P. roqueforti to penetrate it, to species credited with influencing P. roqueforti’s production of methyl ketone – the flavour constituent believed to make blue cheese taste blue.

If the flavours of legendary cheeses are produced by complex communities of yeasts, moulds and bacteria, when it comes to another age-old product – beer – the vast majority are far simpler affairs, usually brewed by a single Saccharomyces yeast culture. But in recent years, a brewery unlike any other has inspired a “sour beer” revolution that’s bringing a host of new flavours to the beer world – Brasserie-Brouwerij Cantillon.

As the last producer in Brussels of the city’s quintessential ale, known as Lambic, Cantillon’s brews are delectably vinous, bracingly sour and, unlike 99.5 per cent of the beer in the world, aren’t produced from commercial yeasts.

“Until recently, Lambic was the last beer in the world created by natural fermentation,” says Jean Van Roy, a fourth-generation Cantillon brewer. “In a way, the beer we make is a product from another era.” After boiling, the wort (unfermented beer) cools overnight in an open-topped copper vat in the brewery’s attic.

Exposed there to ambient wild yeasts and bacteria, it begins fermenting spontaneously like ales of ancient times. “Around a hundred yeasts are involved in the creation of our beer,” says Van Roy (Brettanomyces – feared by winemakers but loved by Lambic brewers – are key). “This diversity helps explain why Lambics are so complex.”

The Senne River Valley surrounding Brussels influences this ambient microbial life, but so does the historic Cantillon brewery itself. “Brewing in a building for decades on end creates a microflora specific to that place, living on ceiling beams and barrels alike. It’s an ecosystem which contributes to the beer’s natural fermentation, a terroir if you like, which we take great care to preserve!”

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