Non-Saccharomyces Yeast in Winemaking

The use of S. cerevisiae as a starter culture is the most widespread practice in winemaking. There is, however, an interest in conducting uninoculated fermentations. An uninoculated fermentation is often referred to as a "spontaneous" or "native" fermentation involving the sequential action of various non-Saccharomyces and indigenous Saccharomyces yeasts. The use of "mixed starter" of non-Saccharomyces with strains of Saccharomyces cerevisiae provides an alternative to both “spontaneous” as well as inoculated fermentations. The possible benefits include added complexity, enhanced ability to secrete enzymes important in the production of aroma compounds, and a fuller palate structure.

The ability of non-Saccharomyces yeasts to produce wines with distinct flavor profiles has increased interest in the use of such yeasts in mixed starters. In addition, research demonstrating the ability of non-Saccharomyces yeasts to lower the alcohol content of wines, control wine spoilage, and improve additional wine properties has been reported. 

Grape musts naturally contain a mixture of yeast species, and therefore, fermentation is not a "single species" fermentation. During crush, the non-Saccharomyces yeasts on the grapes, cellar equipment and in the environment may come in contact with the must. Cellar surfaces play a smaller role than grapes as a source of non-Saccharomyces yeasts. 

It is believed that a selected and inoculated strain of S. cerevisiae will suppress any "indigenous" non-Saccharomyces species and dominate the fermentation process. However, several studies have shown that non-Saccharomyces yeasts can persist during fermentations inoculated with pure cultures of S. cerevisiae. 

Non-Saccharomyces yeasts are thought to be sensitive to sulfur dioxide (SO₂), poor fermenters of grape must, and intolerant to ethanol. It is generally accepted that non- Saccharomyces yeasts, not initially inhibited by SO₂, would not survive during fermentation due to the combined toxicity of SO₂ and alcohol. However, research has shown high numbers (10⁶-10⁸ cells/ml) and persistence of non-Saccharomyces yeasts in some wine fermentations, suggesting their potential role in winemaking. 

There are two general practices of inoculation when using non-Saccharomyces yeasts in mixed starters. The first, co-inoculation, involves the inoculation of the selected non-Saccharomyces yeasts at high cell concentration along with S. cerevisiae. The second practice, sequential inoculation, allows initial inoculation of selected non-Saccharomyces yeasts at high levels, which are allowed to ferment on their own for a given amount of time before S. cerevisiae is added to complete the fermentation. Although both are viable, potential interactions between yeast could determine which strategy is more appropriate. Today, there are many non-Saccharomyces strains available that are compatible with Saccharomyces strains for the improvement of wine, primary aroma. See below.

The most frequently studied species include Torulaspora delbrueckii, Metschnikowia pulcherrima, Candida zemplinina, Hanseniaspora species, and Lachancea thermotolerans).

These yeasts are usually poor fermenters, therefore S. cerevisiae (either indigenous or inoculated) is necessary to take the fermentation to completion. Typically, non-Saccharomyces yeasts have been used in sequential fermentation where they grow or ferment prior to inoculation with S. cerevisiae.

Why use non-Saccharomyces yeast? 

What do these "native" yeasts have to offer winemakers, and how can they be utilized in a planned and controlled manner to produce desired wine styles? Recently, consumer and market demand for lower ethanol wines has driven some research to develop various approaches to produce these wines. Several studies have reported lower ethanol yields when using non-Saccharomyces yeast. In addition, some non-Saccharomyces yeast can utilize sugars with the production of desirable esters and other flavor/aroma compounds with the added advantage of only minimal production of ethanol. 

The variety of flavor/aroma compounds produced by different non-Saccharomyces yeasts is well documented. The compounds produced by different Saccharomyces yeasts include terpenoids, esters, higher alcohols, glycerol, acetaldehyde, acetic acid, and succinic acid. Wine color may also be affected by non-Saccharomyces yeast. Conversely, the improper use of non-Saccharomyces yeasts may result in serious fermentation issues, including stuck/sluggish fermentation, high levels of acetic acid and ethyl acetate, as well as lack of reproducibility, etc. The goal of the winemaker is to emphasize the positive impact of non-Saccharomyces wine yeasts while minimizing its negative impact. 

Conclusion 

There are potential benefits of the use of non-Saccharomyces yeast in wine production; the abundance of grape yeast biodiversity presents many opportunities to explore their use. Strain selection is of key importance, as not all strains within a species will necessarily show the same desirable characteristics. The goals of many researchers have included efficient sugar utilization, enhanced production of volatile esters, and enhanced liberation of grape terpenoids to improve wine flavor and other sensory properties. These goals can be met by selected non-Saccharomyces wine yeast and their proper use in the winery. 

Please contact me or your Scott Labs representative with any questions. 

Biodiva Yeast: This Yeast was initially sold in a pre-blended kit, partnered with a specific S. cerevisiae strain, but now is isolated for winemakers who can match it with a compatible S. cerevisiae of their choosing for both red and white wines. This isolated yeast makes developing wine more customizable. After creating your own blend, the resulting wines will have more intense aromas, mouthfeel, and complexity. The S. cerevisiae strains compatible with Biodiva are 43, BDX, ICV D254, L2056, QA23, and VRB.

Flavia Yeast: This yeast is a pure culture of Metschnikowia pulcherrima, which is selected for its ability to produce aroma and flavor revealing enzymes. Flavia is best used for creating aromatic whites and rosés. Flavia will enhance the aroma and flavor profiles of wines, optimizing varietal characteristics while bringing freshness and volume in the mouth.