In the first part of our series on wine yeasts, Westgarth Wines wine specialist Maurizio Broggi explored wine yeasts and reveals how their behavior influences aroma, structure, style, and quality. In Part II, cultured yeasts, fermentation styles, and the role of the winemaker are in focus.

Cultured yeasts are commercial strains that have been selected and packaged for use in inoculating grape juice to achieve reliable fermentation. Commercial yeast strains are now widely used, providing not only predictable fermentations but also greater stylistic control. A large number of cultured yeast strains are available on the market. Some winemakers and wine critics argue that the widespread use of cultured yeasts has led to stylistic uniformity. Nevertheless, inoculation is widely practiced and is estimated to account for a majority of global wine production. The main appeal of cultured yeasts lies in their reliability: selected strains ferment efficiently, tolerate specific conditions, and can be chosen for their sensory attributes.

Cultured yeast strains are often selected for their suitability to specific fermentative conditions, such as alcohol tolerance, fermentative strength, low production of volatile acidity, low levels of hydrogen sulfides, and suitability for sparkling wine production. They may also be chosen for their ability to enhance varietal character and produce attractive fruity esters. Some cultured yeast strains are used to restart stuck fermentations.

Widely used commercial strains include EC1118, a workhorse yeast valued for its vigor, robustness, and reliability in both still and sparkling wine production. DV10 (the Épernay strain) is prized for traditional method sparkling wines such as Champagne due to its clean fermentation profile, reliability under CO₂ pressure, and strong flocculation capacity, which facilitates easier removal of lees sediment.

Whether to inoculate or not remains one of the more ideological debates in modern winemaking. Inoculated fermentation offers consistency, a rapid onset of fermentation, reduced risk, and greater control over the wine’s aromatic profile. These advantages are difficult for many winemakers to ignore, particularly when managing large volumes of wine or working with compromised fruit.

In many Old World regions, native fermentations are often rooted in tradition. More generally, however, winemakers may choose native fermentations for stylistic reasons, as they are believed to contribute nuance, complexity, and a sense of individuality resulting from greater microbial diversity. This view is often linked to the idea that spontaneous fermentation can enhance the expression of terroir.

These potential benefits, however, come with greater unpredictability and risk. Spontaneous fermentations frequently show longer lag phases – the initial adjustment period before fermentation begins – and increased variability. If fermentation is slow to start, spoilage organisms such as Acetobacter can gain a foothold. To reduce this risk, some producers prepare a so-called pied de cuve: a small batch of grape juice fermented with native yeasts until Saccharomyces cerevisiae becomes dominant, which is then used to inoculate the main fermentation.

Sugar is the primary energy source for yeast, while nitrogen is the most critical nutrient for healthy fermentation. A lack of nitrogen may lead to sluggish or stuck fermentations, as well as increased production of hydrogen sulfides, resulting in unpleasant aromas such as rotten eggs or cabbage. Under normal conditions, grape juice provides sufficient nitrogen in the form of amino acids and ammonium. However, deficiencies may occur in underripe, rotten, or heat-damaged grapes, or in grape juice that has been overly clarified. In such cases, supplemental nitrogen may be required. Diammonium phosphate (DAP) is a commonly used nitrogen source, valued for its affordability and the readily assimilable form of nitrogen it provides to yeast.

Winemakers have several tools at their disposal to influence the composition and activity of microbial populations during fermentation. Early inoculation at relatively high yeast populations limits the influence of wild yeasts. Good sanitation and hygiene reduce the reservoir of resident yeast strains in the winery. Sulfur dioxide additions restrict many unwanted native and spoilage yeasts, and controls fermentation temperature. Together with maintenance of a lower pH, it further reduces the growth and competitiveness of non-Saccharomyces and spoilage microorganisms.

Conversely, winemakers seeking to encourage non-Saccharomyces populations may delay or avoid inoculation or limit early sulfur dioxide additions. They may also maintain low temperatures or add nutrients early to favor wild microflora over Saccharomyces strains. Some producers adopt hybrid strategies. An example of this is a prolonged cold soak without sulfur dioxide, which may encourage wild populations early on. This can be followed by later inoculation with a cultured yeast to ensure that Saccharomyces cerevisiae completes the fermentation.

Yeasts are fundamental to the transformation of grape juice into wine, influencing both fermentation behavior and final wine style. Although Saccharomyces cerevisiae is the most dependable yeast under typical winemaking conditions, other yeast species can play a meaningful role, particularly during the early stages of spontaneous fermentations. Decisions around inoculation, sulfur dioxide use, temperature, nutrient management, and cellar hygiene all shape which yeasts become active during fermentation.

1. What distinguishes cultured yeasts from native yeasts?

Cultured yeasts are commercially selected strains added to grape juice for predictable, reliable fermentation. Native yeasts occur naturally in vineyards and wineries, driving spontaneous fermentations with more variability but potentially greater complexity.

2. Why do winemakers choose inoculated fermentation?

Inoculation is one of the wine fermentation styles that provides consistency, swifter fermentation onset, lower risk of spoilage, and more control over aromatic outcomes – benefits especially valuable for large production volumes or compromised fruit.

3. What is a pied de cuve and why is it used?

A pied de cuve is a small pre-fermented batch of grape juice using native yeasts until Saccharomyces cerevisiae becomes dominant. It is then used to seed the main ferment, lowering lag time and spoilage risks in spontaneous fermentation.

4. How can nutrient deficiencies impact fermentation?

Low nitrogen levels can lead to sluggish or stuck fermentations and higher hydrogen sulfide production, causing unpleasant aromas. In such cases, winemakers may add nitrogen supplements like DAP in their fermentation management strategy to support healthy yeast metabolism.

Want to read more? Take a look at some of our other blogs:

• • An introduction to wine yeasts: Part 1
  • Sulfites in wine: Part I
  • Vine longevity: the beauty of old vines