Fundamental Understanding of Non-Saccharomyces Yeasts: New Options in Modern Winemaking

In modern winemaking, yeast selection technology continues to evolve constantly. A recurring phenomenon is observed where specific yeasts gain attention due to outstanding performance in competitions or industry recommendations, leading to rapid expansion in their adoption in subsequent vintages.

The range of yeast options available for winemaking is extremely diverse, making it impractical to comprehensively evaluate all yeasts listed in commercial catalogs. Furthermore, the addition of spontaneous fermentation using wild yeasts as an option means that the diversity of yeast strains used continues to expand year by year. In such circumstances, it is not difficult to imagine the challenges winemakers face in selecting the optimal yeast.

Amid this diversification of yeast selection, non-Saccharomyces wine yeasts have attracted particular attention in recent years. These yeast groups are highly valued for their potential to achieve the distinctive characteristics of spontaneous fermentation, which could not be obtained through conventional winemaking techniques, in a safer and more controlled environment.

This article aims to deepen fundamental understanding of non-Saccharomyces yeasts and examines their essence and practical applications in detail.

The Relationship Between Non-Saccharomyces Yeasts and Wild Yeasts

When discussing non-Saccharomyces yeasts, one of the most frequently asked questions is whether "non-Saccharomyces yeasts are the same as wild yeasts." This question naturally arises because explanations of these yeast strains frequently use expressions such as "achieving effects similar to spontaneous fermentation."

To state the conclusion first, non-Saccharomyces yeasts and wild yeasts are not synonymous. More precisely, not all wild yeasts are classified as non-Saccharomyces yeasts.

The Essential Definition of Wild Yeasts

The terms "wild yeasts" or "indigenous yeasts" are primarily used as contrasting concepts to commercial dried yeast products circulating in the market. Their definition is extremely broad, meaning "yeasts that exist in nature," and does not encompass any more specific taxonomic characteristics.

Traditionally, the mainstream of winemaking yeasts has been dominated by a single yeast species, Saccharomyces cerevisiae. Since the majority of dried yeast products circulating in the market belonged to this lineage, the equation "dried yeast = Saccharomyces yeast" was established. From this situation, it is believed that the erroneous association "non-dried yeast = non-Saccharomyces yeast = wild yeast" emerged.

However, this perception is based on fundamental misunderstanding. Wild yeasts simply refer to "yeasts that have not been processed as dried yeast products" and do not necessarily mean yeasts other than Saccharomyces strains.

Commercial dried yeast products are also strains derived from nature when their origins are traced. These yeasts are either strains isolated from nature and improved through crossbreeding and selection, or those commercialized in their natural state as collected from nature. In either case, the starting point is wild yeasts that existed in nature—that is, indigenous yeasts.

Therefore, the concept of wild yeasts equally includes both Saccharomyces and non-Saccharomyces yeasts. Equating wild yeasts with non-Saccharomyces yeasts is not scientifically accurate.

Differences from Spontaneous Fermentation

The use of non-Saccharomyces yeasts and winemaking through spontaneous fermentation may appear similar on the surface, but they are actually distinctly different winemaking techniques.

In spontaneous fermentation, it can indeed be said that non-Saccharomyces yeasts are likely to be involved. However, simultaneously, it is impossible to predict the types of yeasts involved or their dominance in this fermentation mode. The possibility that non-Saccharomyces yeasts are not involved at all in spontaneous fermentation also exists, albeit with low probability.

Interestingly, the proportion of Saccharomyces yeasts present on grape skins is reported to be only a few percent of the total in many studies. Based on this figure alone, one might expect that non-Saccharomyces yeasts would play a dominant role in spontaneous fermentation.

However, competition between microorganisms is a far more complex and dynamic phenomenon than expected. Many cases have been reported where non-Saccharomyces yeasts, which occupied the overwhelming majority at the start of fermentation, die off in a short period, and Saccharomyces yeasts, which were in the minority, dominate the entire fermentation process. The succession of microbial communities in spontaneous fermentation is an extremely fluid and unpredictable phenomenon.

In contrast, winemaking techniques that intentionally use non-Saccharomyces yeasts aim to eliminate such uncertainty as much as possible and reliably achieve fermentation by specific yeasts. This can be described as an attempt to reproduce the randomness of spontaneous fermentation in a controlled environment.

However, to achieve such controlled fermentation, appropriate environmental preparation and technical management are essential, regardless of the yeast lineage used. These artificial manipulations have aspects that contradict the philosophy of spontaneous fermentation. In particular, ensuring that specific non-Saccharomyces yeasts reliably fulfill their expected roles requires more sophisticated technical intervention.

Background to the Growing Attention to Non-Saccharomyces Yeasts

The concept of incorporating non-Saccharomyces yeasts into the winemaking process has a history of nearly 20 years in the research field. In actual winemaking settings, producers adopting this approach have been steadily increasing over the past several years. While this is not necessarily the latest technological innovation, its proliferation shows gradual development.

In the early stages, hybrid strains of Saccharomyces and non-Saccharomyces yeasts, as well as mixed culture products using both lineages, were commercialized. Subsequently, products pre-blended with both yeast lineages also appeared in the market. In recent years, products composed solely of non-Saccharomyces yeasts have been fully launched, significantly expanding the number of adopters of this technology.

Currently, yeast product development has become active, and it has become easy to find 100% non-Saccharomyces yeast products in catalogs. The role played by products such as Laffort's Alpha in this market expansion is particularly noteworthy.

Growing Demand for Wine Differentiation

Traditionally, many non-Saccharomyces yeasts have been collectively treated as spoilage yeasts. While it was known that these yeasts impart unique aromas and characteristics to wine that are not produced by Saccharomyces yeasts, these characteristics were mainly avoided as having adverse effects on wine quality.

In fact, many non-Saccharomyces yeast strains have been confirmed to produce acetic acid-type aromatic compounds, and even in the current situation where their active use is being considered, their handling requires careful attention.

However, interest in these yeasts as a means of differentiating wine characteristics has been steadily growing. Behind this lies the global standardization of winemaking technology.

In the modern wine industry, winemaking equipment and environmental control technology have become standardized on an international scale. We live in an era where producers around the world can use similar stainless steel tanks and wooden barrels, introduce identical temperature control systems, and select the same yeast products. Even with differences in the characteristics of grapes as raw materials, homogeneity in fundamental aspects of the winemaking process has become unavoidable.

In such circumstances, non-Saccharomyces yeasts, which were rarely used previously, are attracting attention as a means of imparting uniqueness to wine.

As mentioned above, the fact that non-Saccharomyces yeasts have become available as commercial products has also accelerated this trend. While using unknown spoilage yeasts involves considerable risk, products with detailed usage instructions significantly reduce that risk. Additionally, the psychological reassurance provided by commercialization also serves as a factor promoting adoption.

The fact that the difficulty of using means to achieve novelty has decreased while demand for novelty has increased has become an important element supporting current popularity.

Practical Applications of Non-Saccharomyces Yeasts in Winemaking

Using non-Saccharomyces yeasts in winemaking may sound conceptually simple, but practical application involves considerable complexity.

Current yeast product catalogs list a vast number of products, but the majority—probably 80% to 90%—are Saccharomyces yeasts. This means that yeasts classified as Saccharomyces encompass such a diverse range of strains.

What is important is that these Saccharomyces yeasts represent only a single lineage within the entire yeast spectrum. All remaining yeasts are classified as non-Saccharomyces. In other words, an unimaginably large number of non-Saccharomyces yeasts exist in nature.

However, among this vast number of non-Saccharomyces yeasts, those with characteristics suitable for winemaking are limited. As has been pointed out traditionally, many complete spoilage yeasts that only have harmful effects on wine also exist, so it is not the case that any non-Saccharomyces yeast will do.

Using non-Saccharomyces yeasts in winemaking means selecting and using yeast strains that have characteristics that do not adversely affect wine and do not belong to the Saccharomyces lineage. This selection requires advanced specialized knowledge and careful judgment.

A further important point is that in many cases, it is difficult for non-Saccharomyces yeasts alone to completely finish alcoholic fermentation. Due to limitations in alcohol tolerance and fermentation speed issues, combined use with Saccharomyces yeasts is generally recommended. This is an important measure to avoid fermentation troubles that may occur with single use and to guarantee reliable fermentation completion.

In this combined system, a stepwise process is adopted where non-Saccharomyces yeasts are active in the early stages of fermentation, imparting unique characteristics to the wine, after which Saccharomyces yeasts take over to complete fermentation. Depending on how this process is managed, problems may arise where fermentation does not proceed properly, or results may not achieve the expected taste and aroma.

New Options for Producers Prioritizing Quality Stability

In grape must fermentation, an approach that minimizes artificial intervention and leaves matters to nature can be described as accepting uncertainty. While human intervention generally keeps results within a predictable range, refraining from intervention creates the possibility of achieving excellent results that exceed expectations. This sense of expectation is one of the attractions of spontaneous fermentation.

However, such expectations of chance inevitably carry the risk of producing wine of quality that cannot succeed as a commercial product. Particularly regarding yeasts, those that have positive effects on wine are extremely limited, with the majority being either neutral or having adverse effects. From a probabilistic perspective, the possibility of benefiting from spontaneous fermentation is not high.

Therefore, for producers who prioritize product quality stability above all else, spontaneous fermentation becomes a difficult option to adopt. Even understanding its merits, unavoidable risks prevent decision-making.

Commercialized non-Saccharomyces yeast products provide solutions that reduce such hesitation. They offer the possibility of imparting complexity to wine similar to that obtained through spontaneous fermentation while reducing anxiety due to unpredictability. Rather than unknown diverse yeast groups, they guarantee pure non-Saccharomyces yeasts whose characteristics and effects are clearly understood. These characteristics are what producers aiming for stable winemaking have long sought.

However, attention must be paid to the concept of "stability" here. Stability in this context means predictability of results, not technical simplicity. Appropriate use of non-Saccharomyces yeasts requires greater technical understanding and more precise management than before.

Technical capability is essential to carefully monitor yeast activity at each stage of the fermentation process and make appropriate adjustments when necessary. The ability to comprehensively manage diverse elements such as temperature control, nutrient supplementation, pH adjustment, and oxygen supply is required.

Future Prospects and Possibilities for Technological Innovation

The types of yeasts included in the non-Saccharomyces classification are extremely diverse, and their numbers are vast. It has been pointed out that these yeasts significantly change their effects on wine depending on usage methods, and it is expected that more types of non-Saccharomyces yeasts will be commercialized in the future, with usage methods different from conventional ones also being proposed.

Interestingly, in current technological trends, combined use with Saccharomyces yeasts is recommended in utilizing non-Saccharomyces yeasts. A situation has emerged where non-Saccharomyces yeasts so diverse that their exact number cannot be grasped are being used in combination with equally diverse Saccharomyces yeasts.

This diversity of combinations theoretically holds possibilities that are nearly infinite. Each combination has the potential to create unique flavor profiles and may open new horizons in the development of winemaking technology.

However, this diversity simultaneously increases the complexity of selection. Producers need to gain deeper understanding and experience to find the optimal combination for their desired wine style.

Conclusion: The Essential Value of Non-Saccharomyces Yeasts

Non-Saccharomyces yeasts are a broad concept encompassing all yeasts other than Saccharomyces yeasts, which have traditionally dominated winemaking. While opportunities for their use in winemaking have been limited until now, they are attracting attention as a powerful means of creating wines with unique characteristics unlike any before, precisely because of this limited use.

In previous winemaking technology, spontaneous fermentation has been adopted as a similar approach. In this method, wine is produced by fermenting grape must with yeasts existing in nature, called wild yeasts or indigenous yeasts. While non-Saccharomyces yeasts may indeed be involved in spontaneous fermentation, since Saccharomyces yeasts also exist in nature, spontaneous fermentation does not necessarily mean fermentation by non-Saccharomyces yeasts.

Furthermore, since an immeasurable variety of yeasts exist in nature, the possibility is not small that even non-Saccharomyces yeasts may include those that bring harm to wine.

In response to this situation, movements to commercialize selected non-Saccharomyces yeasts as dried yeasts to achieve specific effects have begun in earnest. These products clearly state usage methods, precautions, and expected effects. By using such yeasts, it has become possible to incorporate characteristics that previously could only be obtained through spontaneous fermentation into wine with lower risk and more effectively.

Currently, non-Saccharomyces yeasts, whose usage opportunities are expanding in winemaking, are positioned as new options that impart unprecedented characteristics to wine while simultaneously improving quality predictability.

Certainly, the surprise due to the chance nature of spontaneous fermentation may be lost. However, not all chance encounters in spontaneous fermentation are desirable. The result of eliminating undesirable elements from such chance encounters may be close to wine achieved through commercialized non-Saccharomyces yeast products.

Saccharomyces yeasts have become overly standardized through years of use, and this has led to a lack of freshness, resulting in attention shifting to non-Saccharomyces yeasts. However, in practical applications, combined use of non-Saccharomyces and Saccharomyces yeasts is recommended. Through such combinations, the role of completing fermentation is entrusted to Saccharomyces yeasts. In wine fermentation, the central role still belongs to Saccharomyces yeasts.

Through this technological development of utilizing previously unused yeasts, the possibilities of winemaking have expanded further, and continuous evolution is expected in the future. The utilization of non-Saccharomyces yeasts will continue to enhance their value as an important component of technological innovation in the wine industry.