oenology

Fundamentals and Applications of Non-Saccharomyces Yeasts: New Possibilities in Wine Production

The role of microorganisms in winemaking has been extensively studied throughout its history. Saccharomyces cerevisiae, which has long been the focus of attention as the primary agent of alcoholic fermentation, has become indispensable in modern winemaking due to its stable fermentation capacity and high ethanol tolerance.

However, in recent years, interest has been growing in yeast groups other than S. cerevisiae, namely non-Saccharomyces yeasts. These yeasts were traditionally treated as detrimental to fermentation. In reality, however, it has become clear that they possess the potential to contribute to wine quality improvement. Particular attention has been focused on their potential to diversify wine aroma compounds and enhance flavor complexity.

This article examines the basic characteristics of non-Saccharomyces yeasts, their specific applications in winemaking, and future prospects. We will also demonstrate how understanding and properly controlling the characteristics of these yeasts can enable more diverse wine production.

1. Basic Characteristics of Non-Saccharomyces Yeasts

1.1 Representative Species and Their Features

Non-Saccharomyces yeasts include a wide variety of species. Representative species include: Kloeckera apiculata, Hanseniaspora uvarum, Candida stellata, Candida pulcherrima, Torulaspora delbrueckii, Kluyveromyces thermotolerans, and Pichia kluyveri.

These yeasts were traditionally thought to be unable to compete with S. cerevisiae during alcoholic fermentation and to die off without surviving until the later stages of fermentation. However, it has become clear that not all of these yeasts behave this way. Some species have been confirmed to have the ability to proliferate to cell populations comparable to Saccharomyces yeasts and maintain consistent cell numbers until the end of fermentation. This proliferation characteristic becomes an important factor in the fermentation process.

Particularly noteworthy is that these yeasts begin proliferation earlier than S. cerevisiae. They start full-scale growth one day after inoculation and play important roles in the early stages of fermentation. This early proliferation characteristic may significantly influence aroma compound formation during early fermentation.

1.2 Regional Characteristics and Environmental Factors

The presence of non-Saccharomyces yeasts varies significantly by region and environment. Although grape cultivation and winemaking involve diverse variables worldwide, the yeast species generally found in grapes and wines are similar globally. However, clear differences are observed in the proportions of yeasts in different regions. These differences may become important factors in forming the unique characteristics of wines from specific regions.

Particularly in regions with high rainfall during harvest, the numbers of non-Saccharomyces yeasts tend to increase. Generally, 9-15 species of culturable yeasts can be identified on grapes, and it has been reported that the existing species and their proportions change according to the survey period. Such changes in yeast flora due to environmental factors may directly impact wine quality.

The reason for increased detection of non-Saccharomyces yeasts in recent years is presumed to be that the modernization of brewing equipment and technology has improved cellar sanitation conditions, and reduced SO2 usage has improved the survival rate of non-Saccharomyces yeasts. Such changes became possible for the first time through the modernization of winemaking. At the same time, they can be considered as new possibilities that did not exist before.

It should be noted that wild yeasts, as generally referred to, do not necessarily mean non-Saccharomyces yeasts. Saccharomyces yeasts also exist in nature, and it is important to note that so-called wild yeasts include such Saccharomyces yeasts as well.

2. Fermentation Characteristics and Metabolites

2.1 Temperature Relationships

The temperature characteristics related to the metabolism or survival of non-Saccharomyces yeasts are important factors in their utilization.

Optimal temperature is said to be highly dependent on the strain. However, even among these, strains that show tolerance to low temperature ranges, dying after 13 days at 15°C and after 21 days at 10°C, have been reported. For strains with high tolerance in such low-temperature environments, the possibility of utilization in low-temperature fermentation has been suggested. This temperature characteristic holds particularly important significance in white wine production.

2.2 Characteristics of Metabolites

Non-Saccharomyces yeasts produce different metabolites compared to S. cerevisiae. These metabolites play important roles as aroma compounds in wine. As aromatic compounds, they particularly tend to produce acetate esters such as ethyl acetate, hexyl acetate, isoamyl acetate, and 2-phenylethyl acetate at relatively high concentrations. They also primarily produce n-hexanol and may produce medium-chain fatty acids and killer factors.

Acetaldehyde production varies by strain. Some strains produce at levels similar to S. cerevisiae, while others produce several times more. It has also been reported that many yeasts show a tendency to produce large amounts of glucose.

Non-Saccharomyces yeasts were previously treated as spoilage yeasts. This was because there were many cases where they produced metabolites with negative effects that were undesirable for wine.

Indeed, considerable numbers of non-Saccharomyces yeasts have been confirmed to have characteristics of producing aromatic compounds that cause so-called off-flavors, including volatile phenols. Additionally, the aforementioned acetaldehyde and glycerol are substances that can potentially become wine defects or their causes. However, it has become clear that some of these defect risks can be avoided by devising fermentation methods. These methods involve mixed fermentation or sequential fermentation, using non-Saccharomyces yeasts and Saccharomyces yeasts simultaneously or in stages. It is also believed that the interactions occurring during such fermentation play a major role in avoiding defects caused by fermentation metabolites.

3. Utilization Methods in Winemaking

3.1 Selection of Fermentation Methods

There are mainly two methods for utilizing non-Saccharomyces yeasts: mixed fermentation and sequential fermentation. This is because non-Saccharomyces yeasts have lower alcohol metabolism capacity than Saccharomyces yeasts, so they cannot completely metabolize sugars in grape juice when used alone.

Mixed fermentation is a method where two yeast species are inoculated simultaneously. Sequential fermentation is a method where non-Saccharomyces yeasts are inoculated first, followed by S. cerevisiae inoculation after a certain period. Each method has specific advantages and challenges.

According to research to date, sequential fermentation is often pointed out as superior for producing more aromatic compounds. However, examination of inoculation ratios is extremely important, and it has been simultaneously pointed out that appropriate ratio settings significantly influence fermentation results.

3.2 Mechanisms of Interaction

The interactions between non-Saccharomyces yeasts and S. cerevisiae can be explained from the following three perspectives:

  1. Securing characteristics with non-Saccharomyces yeasts before S. cerevisiae proliferates
  2. Metabolizing sugars that non-Saccharomyces yeasts cannot completely metabolize with S. cerevisiae
  3. Interactions occurring when S. cerevisiae takes up substances produced during non-Saccharomyces yeast proliferation

These interactions are said to enable the production of complex aroma compounds that cannot be obtained through single fermentation. Through multiple verifications, it has been reported that even when wines fermented individually with each yeast are blended in the same ratio as mixed fermentation, the sensory evaluation results differ from those obtained through mixed fermentation or sequential fermentation.

The scope of effects from interactions is a field where not everything has been elucidated yet. It is expected that extremely complex effects are occurring.

4. Effects on Wine Quality

4.1 Effects on Aroma Compounds

Non-Saccharomyces yeasts significantly affect wine aroma compounds. The production tendency of esters and higher alcohols being different from conventional Saccharomyces yeasts is particularly characteristic.

Due to such characteristics, introducing non-Saccharomyces yeasts into fermentation is expected to produce different types of aromas compared to relying solely on conventional Saccharomyces yeasts, or to increase the quantities of certain aromas. The increase in aroma types and quantity variations are evaluated as producing wines with greater complexity compared to conventional wines.

4.2 Effects on Color

Yeasts affect wine color both directly and indirectly. Direct involvement includes the production of color precursors: vinyl phenol, acetaldehyde, and pyruvic acid. Indirect involvement includes pH changes due to organic acid metabolism. These effects play important roles in the visual quality of wine.

For example, the use of T. delbrueckii yeast has been reported to improve red wine color intensity and flavanols. Additionally, when Schizosaccharomyces pombe and Lachancea thermotolerans are sequentially inoculated, an increase in type A vitisin is expected. These effects may contribute to wine color stability and quality improvement.

Furthermore, P. Guilliermondii strains show high hydroxycinnamic acid decarboxylase activity and may improve the formation of vinyl phenolic pyranoanthocyanins. Additionally, it has been pointed out that Candida valida, Metschnikowia pulcherrima, Kloeckera apiculata, and Starmerella bombicola secrete pectinases, potentially affecting wine color by increasing the extraction of phenolic compounds from grape skins.

5. Future Prospects

Research on non-Saccharomyces yeasts is being actively conducted as opening new possibilities for improving wine chemical composition and sensory characteristics. Since these yeast groups previously had almost no possibility of being involved in fermentation as spoilage yeasts, the impact of their introduction is expected to be significant.

However, the following points require attention in their utilization:

  • Pure culture fermentation often shows multiple negative metabolites and fermentation characteristics
  • Use in re-fermentation processes is not recommended due to unstable behavior
  • In mixed fermentation or sequential fermentation, stability and reproducibility regarding fermentation by-product generation are low, making it difficult to predict results in advance

By overcoming these challenges, it is expected that the potential of non-Saccharomyces yeasts can be maximized.

Conclusion

Research on non-Saccharomyces yeasts opens new possibilities in winemaking. Recently, dried yeasts packaged with non-Saccharomyces yeasts have become commercially available. Such yeast groups that have not been utilized before are attempting to enable more complex and attractive winemaking by understanding their characteristics and controlling them appropriately.

As research continues to advance in characterizing these yeasts and their applications, winemaking technology will continue to develop further. In such processes, purification of characteristics through selection is also expected to progress. Such movements are considered to lead to creating yeasts with more desirable characteristics without genetic modification.

On the other hand, when such attractive yeasts derived from previously unused wild yeasts become commercially available, winemakers and consumers may be required to reconsider whether there are still reasons to choose not to use dried yeasts.

Your Trusted Partner in Winemaking

Are you looking to resolve day-to-day questions and uncertainties in viticulture or winemaking? Hoping to take your wine quality to the next level? We're here to help.

At Nagi Wines, we support every step of your winemaking process—from vine to barrel to bottle. Our seasoned experts provide on-site, hands-on guidance to enhance your knowledge, refine your technique, and elevate the overall quality of your wines.

If you're seeking professional support while keeping costs under control, don’t hesitate to get in touch. Let's craft excellence together.

Contact now

  • この記事を書いた人

Nagi

Holds a degree in Viticulture and Enology from Geisenheim University in Germany. Served as Head Winemaker at a German winery. Experienced viticulturist and enologist. Currently working as an independent winemaker and consultant specializing in both viticulture and enology.

-oenology