Ask Jim: Wild versus commercial yeasts
Our heartiest congratulations to Jim Chatto has recently won the Hunter Valley Winemaker of the Year Award (August 2009). Here we republish some of his earlier articles for VisitVineyards.com
Some producers of top quality wine use so called wild yeasts in the fermentation process. They claim these result in more complex, earthy characteristics in the wine and a lower percentage of alcohol. What are your thoughts on the use of wild yeasts versus commercial yeasts?
Budding winemaker, Tasmania
Wild yeast is the generic term for any yeast, involved in the fermentation, not specifically added by the winemaker. Wild yeasts occur everywhere in our environment, especially the vineyard and winery. The growth of wild yeast is encouraged by many winemakers across an array of wine styles.
Wild yeast occur in and contribute to all fermentations regardless of whether commercial yeast has been added. Typically one yeast strain becomes dominant to the peril of all others. Once a commercial yeast is added the contribution of wild yeast is generally limited to the initial stages of fermentation.
Conducting wild fermentations is a fairly common practice, often resulting in positive attributes in the wine like improved complexity and mouth feel. However, I do not believe it leads directly to lower alcohol, which is a function of yeast strain, temperature and nutrient availability among many other parameters.
The decision to encourage wild yeast fermentation should not be taken lightly as there is a greater degree of uncertainty in the end result. A diligent winemaker should thoroughly understand the vineyards and fruit they are working with and conduct comprehensive trials before diving head first into wild ferments.
Commercial yeast strains are selected by the winemaker for their known attributes such as tolerance to alcohol and temperature as well as flavour production. There is definite comfort and far less risk involved when selected commercial yeast strains are used.
That said I utilise both in my winemaking depending on style, experience and time. I relish the degree of uncertainty and discovery associated with wild yeast, though be it tempered by a winemaker's instinct for control.
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Please note, Jim will endeavour to answer as many questions as he can, however there may be delays between submission of questions and publications. Emails will not receive personal responses.
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