Can Yeast Constitute Terroir? Tracing the Genealogy of Genetics and Distribution

Various factors are considered important elements that contribute to the taste of wine. Among these, how significant would you position yeast as an element?

In wine production, yeast plays an extremely important role. This is universally acknowledged. However, when the discussion turns to its positioning in wine flavor, opinions suddenly diverge. This involves the somewhat oppositional relationship between commercial dry yeast and wild yeast.

Consider elements such as climate, soil, and topography. These elements are, in a sense, fixed components tied to their location. They cannot be substituted. When attempting to make wine in a particular place, there is no choice but to accept the existence of these elements. Even if modifications are made, they require large-scale interventions, and the degree of freedom is never high. Yeast, however, operates under different circumstances. Only yeast offers countless choices.

For this reason, yeast is sometimes included as an element of terroir, and sometimes it is not. Generally, the concept of terroir demands an immutable connection to the land and indigenous character. Therefore, there exists a deep-rooted belief among some that yeast, which floats above the land with available choices, does not conform to the concept of terroir.

Within this terroir philosophy, what becomes important is the existence of wild yeast.

The thinking goes that if it is wild yeast existing in the land—not something introduced by human hands—it could become one of the important constituent elements that align with terroir philosophy.

Currently commercialized dry yeast, if we trace their origins, were also wild yeast that existed in nature. However, in modern times, these are treated as distinct from wild yeast and are often spoken of as if they were completely different entities. One cause of this is insufficient understanding of what wild yeast actually represents.

This article explains the origins of yeast, which are rarely discussed in detail, and the positioning of wild yeast as an entity.

The History of Yeast

For humanity, the history of yeast is none other than the history of humanity's relationship with fermented foods.

Within our current understanding, fermented beverages were already being produced around 7000 BCE in China. About 1000 years later, wine began to be made near Iran, and 3000 years after that, wine production started in Egypt.

While wine gives a strong impression of Europe, wine production began in the European continent relatively late in history. Starting with Greece around 2000 BCE, followed by Italy around 1000 BCE, and wine making is said to have begun in Northern Europe around 100 CE. Wine making reached America around 1500 CE.

Throughout this long period, yeast is believed to have constantly existed near humanity, continuing movement and geographical dispersion along with human migration.

Wine Yeast Originates from the Middle East

Countless yeasts exist in nature. Among these, some are strongly involved in human life while others have no relationship whatsoever. These yeasts are classified into several groups, with one group forming the wine-related yeast group.

Among wine-related strains, particularly Saccharomyces yeasts have been revealed through genetic analysis to have formed through multiple divergences. Most strains forming this group have genes derived from what is called the Lebanese strain at their base, and it has become clear that they originate in Mesopotamia.

This yeast born in Mesopotamia is thought to have subsequently split into groups that dispersed to Mediterranean coastal regions and groups that dispersed to Central Europe.

Relationships Among Different Yeasts

In discussions surrounding wine's origins, it is often said that beer production came first historically, and wine began to be made in imitation of this. However, when examining the genetic characteristics of the yeasts used in each, it becomes clear that this is actually not the case.

This is because genetic analysis has revealed considerable "distance" between the gene groups of yeasts responsible for beer fermentation and those responsible for wine fermentation. These two are genetically distinct entities, and it has become clear that neither technology came first with its yeast being applied to produce the other.

Rather, what bridges the gap between these genetically different beer yeast and wine yeast is bread yeast. Furthermore, it has been suggested that the distant ancestor of Japanese sake yeast may be this bread yeast.

Genetic Diversity of Wild Yeast

When including yeast as a constituent element of terroir, what is expected is the existence of yeast with characteristics unique to that land. This can be rephrased as genetic features observed only in that location.

On the other hand, when examining the evolutionary history of yeast, particularly Saccharomyces yeasts, the influence of domestication is clearly evident.

Most yeasts currently used in wine production, whether through dry yeast or natural fermentation, belong to the Saccharomyces family. Recently, the use of non-Saccharomyces yeasts has also increased, but when viewing the fermentation process as a whole, it is nearly impossible to complete wine fermentation without Saccharomyces yeast. The characteristics of these Saccharomyces yeasts are their high resistance to ethanol, sulfur dioxide, and copper.

Wine yeast groups are considered relatively diverse populations genetically. However, even within such diversity, the aforementioned resistance is maintained almost consistently. This is considered to be the influence of domestication through long periods of living alongside human life. As a result of humans continuously using them for specific purposes, yeast also evolved adaptations to those environments.

Yeast Independent of Land

For example, bread yeast is said to have strong geographical associations. For expecting yeast as terroir, it would be desirable for wine yeast to be similar, but in reality, it has been found that this is not the case. Wine yeast groups have low geographical dependency.

Research has reported that the major lineages of wine-related S. cerevisiae collected from around the world can be consolidated into 3 to 5 types. Sub-populations are formed within each lineage, and hybridization between these sub-populations has been confirmed. This increases the number of yeast strains, but tracing back to their origins reveals narrow sources with most yeasts being closely related. According to one survey report, genetic variation based on geographical origin of wine yeast accounts for only about 28% of total variation.

Interestingly, however, even in this yeast group that is consolidated in origin and has small geographical variation ranges, genetic diversity is maintained at high levels.

When yeast was collected from a region and its distribution surveyed, it was found that even the most representative strain with the highest population could only achieve about 60% regional occupancy. It has also been reported that such distributions differ approximately every 100 km radius.

This means that while there are few yeasts originating from the land itself, genetic hybridization occurs relatively frequently among yeasts that have come from outside.

The Existence of Vectors Responsible for Yeast Dispersion and Change

The fact that only a few lineages of considerably homogenized strains exist worldwide indicates that yeasts of the same lineage have dispersed throughout the world. However, yeast cannot move by themselves, and their movement always requires the existence of vectors that mediate movement.

The greatest entity responsible for yeast movement has been humanity. Humans expanded their living areas while carrying the food culture they had cultivated, and such movement necessarily included yeast movement as supporters of that food culture.

After being transported by humans, birds and insects further expanded yeast habitats. These entities not only carried short-term yeast dispersion within certain regional ranges but also served as yeast vectors from additional perspectives.

Yeast Overwintering with Wasps

For example, yeast living in wine or inside containers for wine production has a high probability of surviving throughout the year. However, yeast trying to survive in nature after being brought by humans faces different circumstances. They lack means to overwinter.

Natural fermentation in wine production is explained as occurring when yeast attached to grape skin surfaces is brought into the winery along with grapes and becomes active there. As explained here, yeast predominantly inhabits grape skin surfaces because sugar, their food source, exists there.

Yeast are microorganisms, and food sources are essential for their survival. So where are the yeasts that inhabit ripe grape surfaces in autumn when grapes have not yet ripened?

Some are known to inhabit soil and other locations. However, yeast habitats are not limited to these. Hornets are also known to be significant yeast carriers.

It has long been known that multiple yeasts inhabit hornet intestines. When the distribution of intestinal yeasts was surveyed, about 4% of intestinal yeast groups were found to be S. cerevisiae-type yeasts. It was also reported that of 17 collected S. cerevisiae-type yeast strains, 10 were strains capable of participating in wine production.

This survey also confirmed that yeast group composition changes according to grape ripening periods and other factors, with increases and decreases in strain numbers, while S. cerevisiae strains showed little such variation throughout the year, existing stably in intestines regardless of season. It was additionally confirmed that such intestinal yeast environments continue from queen wasps to their offspring.

Yeasts that overwinter in hornet intestines during periods when survival on their own is difficult from autumn to spring subsequently disperse according to wasp foraging behavior. The range of such dispersion is estimated to be approximately 10 km based on wasp behavioral ranges.

Drosophila Responsible for Yeast Change

Drosophila, treated as troublesome in both grape cultivation and winemaking, have been found to significantly influence regional yeast diversity. While Drosophila have short lifespans per generation and cannot function as overwintering vectors like wasps, they have considerable influence on short-term yeast cell dispersion. Moreover, they appear to promote genetic hybridization.

Yeast reproduction normally occurs through cell division methods called cloning or selfing. Wine yeasts, particularly from a genetic perspective, are known to reproduce mainly through cell division.

However, yeast are not incapable of sexual reproduction. Generally, yeasts are said to increase sexual reproduction rates when in starvation conditions. Yeasts taken into Drosophila bodies through feeding behavior face extremely poor survival environments. Under such conditions, yeasts cannot obtain sufficient nutrition, so they switch reproductive methods to sexual reproduction and begin forming spores.

Yeast spores become tetrads—structures where spores are connected by sporular bridges. Within these structures, spores maintain close proximity to each other, so normally there would be extremely high probability of nearby spores further mating with each other, causing inbreeding. However, in Drosophila intestinal tracts, enzyme activity destroys these tetrad structures, separating individual spores. This physical distancing of spores makes inbreeding less likely to occur.

Spores in this state have dramatically increased possibilities for outbreeding with spores from different parents, either within Drosophila intestinal tracts or after being expelled externally.

Survey cases estimate that passage through Drosophila intestinal tracts increases yeast outbreeding possibilities by more than 10 times, with occurrence rates per generation estimated at 1.1 to 3.5%.

It has been found that different yeasts show varying attraction to Drosophila. This difference averages about 2.6 times, and this attraction difference has been found to influence fly reproduction rates.

Yeasts with higher attraction have greater possibilities of being taken up by Drosophila, resulting not only in more opportunities for spatial dispersion but also potentially leading to genetic diversity acquisition.

Long-Distance Movement via Birds

Recently, birds have become recognized as long-distance mediators of microorganisms. Italian research found that yeast survival periods when taken into bird intestines are approximately 12 hours. Though varying by bird species, the dispersion range calculated from this survival time is estimated at approximately 300 to 350 km.

This survey detected 125 total yeast cells from about 33% of bird specimens, identifying 18 species of brewing-related yeasts including S. cerevisiae.

It has been confirmed that migratory birds with low body fat percentages that make frequent stops at relay points play greater roles in yeast dispersion.

Regional Character of Yeast and Their Distribution

As already seen, wine yeast strains found worldwide have essentially no regional character in terms of their roots. However, yeasts that reach each region acquire genetic diversity in those regions through various mediators, and these changed strains spread regionally through vectors.

Research has indicated that such yeast communities form approximately every 100 km radius. Within this range, genetic homogeneity is high regardless of habitat, while this uniformity is lost beyond this range, as reported through multiple surveys.

An example of European yeast strains hybridizing after moving to new locations is hybridization with yeast species inhabiting oak trees in the northern hemisphere. This hybridization may have occurred quite frequently and is suggested to have had considerable influence on wine strain genetic composition. Current wine strain genetic composition is known to include oak-type genes as ancestors in considerable proportions.

Subspecies formation through such hybridization in destination regions likely ensures yeast existence as a component of what is called terroir.

Is That Yeast Really Rooted in the Land?

Even if fundamental roots are the same, S. cerevisiae is genetically prone to mutation and actually confirmed to have great diversity. Moreover, within regions, dispersion and outbreeding occur via birds and insects, with traces of regional hybridization genetically confirmed. Therefore, unique regional yeasts exist and undoubtedly contribute to terroir construction. There is a desire to reach this conclusion. However, it is probably fair to say that we cannot yet definitively state this.

As was the case in early American winemaking, yeast has been spread worldwide through human hands. Even if not across such wide ranges, yeast moves extensively through processes of collecting grapes from various locations for wine production. Survey results actually report that lands collecting grapes from wider ranges for wine production show greater yeast genetic diversity. Yeast moves across countries and regions with such ease.

Furthermore, in current times when production areas have become somewhat fixed, the powerful vector responsible for long-distance yeast movement is not birds but wooden barrels, primarily barriques.

Multiple genetically different yeast strains including S. cerevisiae have been detected from new barrels delivered to wineries. Moreover, the most numerous yeast cells detected from naturally fermented juice were strains genetically matching yeast cells detected from unused barriques. This clearly indicates that yeasts brought from other regions are powerfully involved in terroir-utilizing fermentation in those regions.

It has also been pointed out that yeasts brought via barrels may further hybridize locally. Currently, this hybridization rate is estimated at approximately 30%.

The possibility that commercial yeasts used within wineries disperse to nearby vineyards and oak trees has also been indicated. One survey reported that genetic sharing between locally collected yeast cells and commercial strains exceeded 40%.

The Concept of Dynamic Equilibrium in Yeast Flora

Many wineries purchase considerable numbers of new barrels annually. This means considerable numbers of yeasts are newly introduced from outside regions each year. Such yeasts may directly become sources of natural fermentation or may disperse while hybridizing locally, with results contributing to yeast geographical dependency below 30%.

This is not about whether individual wineries use barrels or not. At minimum, the confirmation of yeast genetic identity within 100 km ranges suggests that everyone may equally receive influences of changes existing within 100 km. If bird mediation is involved, this range may expand to approximately 300 km. The relationship between yeast and terroir is probably more complex than generally conceived, existing within dynamic relationships.

Yeast is the most important entity indispensable to wine fermentation. Their metabolism greatly influences all aspects of wine taste, aroma, and quality. This entity cannot be ignored when discussing wine characteristics.

However, in modern times when human and material movement has become active, strongly linking these microorganisms to specific regions under terroir concepts has become increasingly difficult. This results from more fundamental movement and dispersion beyond commercial dry yeast use. This exists outside frameworks where dry yeast cannot constitute terroir elements or wild yeast can become part of terroir.

As seen throughout, land-rooted yeast is most likely formed not by unchanging characteristics unique to that land, but by dynamic equilibrium states through continuous influx and hybridization. Yeast flora constantly changes, and natural fermentation occurs through yeast communities existing at that location at that time.

When seeking to give wine individuality, grounding that wine in its production location is natural in current wine consumption. However, the possibility that one important element determining wine essence actually lacks immutable indigenous character must always be kept in mind.

Terroir thinking has aspects of trying to express wine quality and characteristics as equally immutable by connecting wine with immutable elements. Recently, however, many elements thought immutable are being recognized as changeable. In turn, environments are being established where wine individuality and quality assurance may be viewed as not immutable.

Climate, environment, and yeast too. When reconsidered as changeable entities, what meaning would yeast, as more changeable entities, have, and what importance would be given to them? What is wild yeast, and what is its value? The time seems to have come for reexamination along with this background.