Spontaneous Fermentation

Definition

Spontaneous fermentation (also known as wild fermentation or natural fermentation) describes the process of alcoholic fermentation without the addition of cultured yeast. Instead, naturally occurring wild yeasts that live on grape skins and in the winery take over the conversion of sugar into alcohol. This traditional method is regarded as the most original form of winemaking and is increasingly valued by producers seeking to create authentic, terroir-driven wines.

How it works

In spontaneous fermentation, the winemaker deliberately refrains from using industrially cultivated yeast strains. After harvest and pressing, the naturally present yeasts — primarily Saccharomyces cerevisiae, but also other strains such as Kloeckera, Candida, and Hanseniaspora — begin the fermentation. This process unfolds in several phases:

1. Start phase: Non-Saccharomyces yeasts dominate initially, generating more complex aromas
2. Main fermentation: Saccharomyces cerevisiae takes over and brings fermentation to completion
3. Finish: Slow tapering of yeast activity

Spontaneous fermentation often takes longer than controlled fermentation with cultured yeasts — sometimes several weeks or even months. Temperature is usually only minimally regulated so as not to disturb the natural course.

Advantages and disadvantages

Advantages:

• Complexity: Different yeast strains generate a broader aromatic spectrum than cultured yeasts
• Terroir expression: The wines more strongly reflect their origin and vintage
• Authenticity: Regarded as the most natural and traditional form of winemaking
• Individuality: Each wine becomes unique, as the yeast population varies from estate to estate

Disadvantages:

• Risk: Greater chance of off-flavours from unwanted yeasts or bacteria
• Unpredictability: Fermentation is harder to control; results vary from year to year
• Stuck fermentation: Spontaneous fermentations can stop before all the sugar has been converted
• Time commitment: Longer fermentation ties up tanks and barrels for months

Aromatic effects

Wines from spontaneous fermentation often display characteristic secondary aromas:

• Yeasty notes: Brioche, fresh bread, pastry
• Spicy components: Clove, white pepper, herbs
• Stone fruit and nuts: Almond, hazelnut, ripe peach
• Floral hints: Meadow flowers, chamomile
• Minerality: Often more pronounced than in wines made with cultured yeast

The diversity of aromas arises from the metabolic by-products of different yeast strains that are active at various stages of fermentation.

Application in modern winemaking

Spontaneous fermentation is practised today mainly by producers who:

• Work biodynamically or organically
• Follow a minimal-intervention philosophy (natural wine)
• Aim to produce terroir-driven wines
• Emphasise tradition and craftsmanship

The method is especially widespread in France (Burgundy, Rhône, Loire), Italy (Piedmont, Tuscany), and increasingly in Germany, Austria, and Switzerland. Many premium producers today combine both approaches: spontaneous fermentation for their top wines, cultured yeast for entry-level wines.

Difference from cultured yeast

In conventional winemaking, the natural yeast flora is eliminated through sulphuring or heating before specially cultivated yeast strains are added. These cultured yeasts guarantee:

• Predictable fermentation results
• Shorter fermentation times
• Reduced risk of off-flavours
• Reproducible aromatic profiles

The price of this control is a narrower aromatic spectrum and less terroir expression. Many producers view spontaneous fermentation as a return to traditional winemaking that brings the character of the vintage and the site unfiltered into the glass.

Hygiene and prerequisites

Successful spontaneous fermentation requires:

• Healthy grapes: Rot or fungal infection encourages unwanted microorganisms
• Clean cellar hygiene: No residues of disinfectants that could kill the yeasts
• Experience: The winemaker must be able to assess the progress of fermentation and its risks correctly
• Patience: Spontaneous fermentations take time and cannot be rushed

Many estates build up a stable, quality-oriented yeast population in the cellar over years, ensuring reliably successful spontaneous fermentations.

Conclusion

Spontaneous fermentation is more than a method — it is a philosophy built on trust in natural processes and the expression of terroir. While it carries greater risks, it rewards both producers and wine lovers with complex, individual wines that tell a story of history and place. In an era of interchangeable industrial wines, this approach is gaining ever greater significance.