The advantages and disadvantages of spontaneous fermentation

by | Dec 1, 2021 | Practical in the cellar, Winetech Technical

Irrespective of origin, cultivar, style or prize winners, all wines share one common factor, namely alcoholic fermentation. The sugar present in the grapes must be converted to alcohol and carbon dioxide, which requires yeast. The yeast can be received with the grapes or it can be added as pure culture yeast.

Louis Pasteur already confirmed the existence and role of yeast in alcoholic fermentation in 1863. Before his observation, yeast had already played a role and spontaneous fermentation was the primary source of fermentation. With the development of yeast technology, it became possible to determine the weak and strong points, opportunities and threats of spontaneous fermentation with a SWOT analysis. In order to do this, it is important to define natural yeast. Natural yeast originates from the grapes, cellar surfaces or atmosphere and can also be seen as wild or indigenous yeast. These yeasts will commence alcoholic fermentation spontaneously, which is usually applied without sulphur dioxide additions.

The microflora of yeasts is very area bound and also differs between vintages. Uncertainty exists concerning the vintage influence, but the region, cultivar, vineyard age, viticultural practices, environment and climate all have an influence on the microflora. Species of Hanseniaspora, Candida, Pichia, Kloeckera, Metschnikowia, Brettanomyces and Saccharomyces, with the ability of alcoholic fermentation have been isolated from vineyards. The spontaneous fermentation of grape juice therefore consists of different populations of different yeast flora. Different species will thus play a decisive role at the different stages of alcoholic fermentation. The temperature and alcohol concentration will especially influence it. The fermentation will also not necessarily be executed by the yeasts occurring on the grapes, but can rather be executed by the Saccharomyces population of the cellar. The accepted pattern of a spontaneous fermentation is often that the non-Saccharomyces species initiate the fermentation, but Saccharomyces yeasts complete it. It is however not necessarily the Saccharomyces cerevisiae species, used by the cellar for other fermentations.

An inoculated fermentation is using a wet culture or dried yeast to initiate and complete the alcoholic fermentation. In most cases it is a yeast strain of the known alcohol resistant, Saccharomyces cerevisiae. It is generally known as wine yeast. As a result of its sunlight sensitivity, it does not occur much on grapes, but usually has big populations in cellars.

The strong points of spontaneous fermentation are the complexity and structure, which it can impart to wine. It is also more terroir driven, because it can cause more unique environmental characteristics. It is also much cheaper than inoculated fermentations. Different genera have different volatile components resulting in a more complex flavour profile. Its structure advantages are mainly as result of the higher glycerol concentrations that are formed, and these characteristics are also incorporated in the development of commercial strains. Seeing that it is known that the yeast flora differs between vineyards, it can exhibit more pronounced differences between wines. The potential weak points of spontaneous fermentations are the following: the longer lag phase before fermentation commences, a lower yeast kinetics, especially at the end of fermentation, potential microbial spoilage, oxidation, stuck fermentation, unpredictability, differences between vintages and, longer tank engagement. It is consequently essential that only sound grapes, with a low micro-population are considered for spontaneous fermentation. Grapes with a high sugar concentration must rather also be avoided, because it is one of the reasons for sluggish or stuck fermentations. As a result of the proven fermentation characteristics, the resistance against lower temperatures and sulphur dioxide and the limited potential of off-flavours with Saccharomyces cerevisiae, the use of spontaneous fermentation is considerably riskier.

Spontaneous fermentation can however offer marketing opportunities to wine. Yeast, which is native to vineyards, creates a home to it, which can be used to promote the distinctive characteristics of wine of specific vineyards. Consumers are increasingly interested to know more about the origin of purchased products, as well as which additives are used during production. This is actually the reason for the interest in and growth of the “natural” wine movement. As a result of the unique characteristics of spontaneous fermented wines, winemakers have more blending possibilities. Spontaneous fermentations can be used together with Saccharomyces inoculations where the fermentations are initiated by the wild yeasts followed by Saccharomyces inoculations to ensure that the fermentation is fluent and will be completed. A new concept is where species of so-called wild yeasts are commercially available to be used as co-inoculants together with Saccharomyces cerevisiae strains. It is especially strains of Saccharomyces uvarum, Hanseniaspora uvarum, Torulaspora delbrueckii and Kluyveromyces thermotolerans that are used. It is however doubtful whether it can be interpreted as spontaneous fermentation, although it may have similar results with a limited risk.

The main threat of spontaneous fermentation is that the style of the resulting wine is not according to expectations, does not comply with personal advantages or can even be spoiled. This implies that the grapes were not utilised correctly and can also have financial consequences. A wrong perception is that spontaneous fermentations need not be managed. As with inoculated fermentations, it must be monitored and controlled. Winemakers have the same aids like pump overs, temperature adjustments and wood maturation to make the necessary adjustments (Wright, 2021).

 

Inoculated yeast ensures a sound fermentation.

 

Reference

Wright, C., 2021. A SWOT analysis of going wild. Wine Business Monthly, June 2021: 32 – 36.

 

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