By definition, yeasting is the addition of oenological yeasts to the must to trigger and stimulate the alcoholic fermentation process. A crucial stage in the winemaking process, this technique requires a precise protocol to guarantee its success and effectiveness.

Focus on the role and benefits of yeast in wine-making

It's based on a simple fact: wine without yeast is impossible! ! But we still need to master the fermentative activity of yeast.... In fact, indigenous yeasts capable of initiating alcoholic fermentation, known as "spontaneous" fermentation, are found naturally in vines and grapes. Nevertheless, their nature, quantity and exact impact on this process remain difficult to predict. And this lack of visibility can sometimes be detrimental to wine quality. Many winemakers therefore choose to to yeast their musts in order to guide alcoholic fermentation. Exogenous yeast strains cultivated in laboratories and selected for their known oenological properties will then supplant their indigenous counterparts, as they are more numerous and more resistant. Yeasting thus facilitates and ensures the safety of this key stage in the winemaking process.

These exogenous yeasts are most often sold in dehydrated form (active dry yeast, or ADY) and belong mainly to the Saccharomyces cerevisiae family of yeasts. There are almost 300 varieties. This wide range enables us to adapt to different types of yeasting, defined by their action on the must. This process can, for example, be carried out to accelerate alcoholic fermentation, or to activate or reactivate it (known as starter yeast), or to facilitate foam formation, etc. But the benefits of exogenous yeasts don't stop there: this type of yeast also conditions the organoleptic properties of a wine (its aromas, taste, color, texture, etc.).Mastery of yeasting, and its appropriateness to the product being vinified and the winemaker's objectives, are therefore of paramount importance.

The yeasting protocol, a winemaking art in its own right

Successful yeasting requires a certain method and a number of steps to prepare the yeast and inoculate it into the must.

  • Store yeast packets properly, at less than 15°C, and check their integrity, best-before date and precautions for use.
  • Select the right yeast(s) (Saccharomyces or others), according to :
    • the type of yeast to be used,
    • les propriétés du moût must properties (white or red grape variety, temperature, alcohol content, acidity, etc.)
    • the desired organoleptic characteristics of the wine.
  • Correctly dose the yeast, with a minimum dose of 20 g/hL and a maximum dose of 40 g/hL. The yeast should be ten times more numerous than the indigenous yeast, in order to establish itself properly in the must.
  • Moderate any sulfiting of musts (addition of sulfur dioxide, or SO2) to encourage the activity of exogenous yeasts. This also helps limit the level of sulfur in the finished wine, as the latter emits SO2 during alcoholic fermentation.
  • Perfectly rehydrate the yeasts in a large volume of warm, sugary water, for an average of twenty minutes. This ensures complete restoration of their plasma membrane, the integrity of which determines their survival and fermenting power.
  • Inoculate as soon as possible after harvest, while gradually acclimatizing the yeast to the must, avoiding thermal and osmotic shocks.
    • For red wines, yeast is added during tank filling, 15 hours after sulfiting, if used.
    • For white and rosé wines, yeast is added immediately after settling.
  • Raise the must at the bottom of the tank (remontage technique) to homogenize it and oxygenate the yeasts.