Fermentation is the moment when grape must stops being juice and begins its transformation into wine. It’s a technical phase - but also a fascinating one - because this is when much of the wine’s aromatic character is created. The aromas you smell in your glass - fruit, flowers, spices, herbs - are born partly in the vineyard and partly during this very process.
Understanding how fermentation works helps us look at wine differently - not just as a beverage, but as the result of a living, evolving transformation.
The Role of Yeasts
Fermentation begins thanks to yeasts - microorganisms that convert the grape’s sugars into alcohol and carbon dioxide. This reaction generates heat and releases hundreds of aromatic compounds.
There are two possible approaches:
- Indigenous yeasts, naturally present on the grape skins and in the winery, which carry a unique, terroir-driven identity but require more careful control.
- Selected yeasts, chosen by the winemaker for safer, more predictable fermentations and specific aromatic profiles.
In both cases, yeasts don’t just produce alcohol—they also create esters, higher alcohols, and other compounds that build the wine’s aromatic bouquet.
Temperature and Timing: A Delicate Balance
The heat produced during fermentation must be managed. If the temperature is too high, delicate aromas can be lost; if too low, the process may slow or even stop.
- White and rosé wines are often fermented at lower temperatures (12–18°C) to preserve fresh, fruity aromas.
- Red wines are fermented at higher temperatures (22–28°C) to extract color, tannins, and more complex aromas.
The duration can vary from just a few days to more than two weeks, depending on the grape variety and desired wine style.
Alcoholic and Malolactic Fermentation
Alcoholic fermentation is the primary stage, but many red wines - and some whites - also undergo malolactic fermentation. Technically, this is not a fermentation but a conversion process, where lactic acid bacteria transform malic acid (sharper and tarter) into lactic acid (softer and creamier).
This stage reduces perceived acidity and introduces creamy, buttery aromas, giving the wine more roundness and approachability.
How Aromas Are Created
During fermentation, aromatic compounds form and combine in complex ways. Some aromas come directly from the grape (primary aromas), others are born during fermentation (secondary aromas), and still more develop later during aging (tertiary aromas).
A Primitivo fermented at a controlled temperature, for example, will develop rich notes of ripe red fruit. A Fiano fermented at low temperatures may reveal citrus and white flower notes with striking clarity.
The winemaker’s hand is crucial: every technical choice - macertation length, container type, fermentation temperature - shapes the final aromatic profile.
In summary, fermentation is a pivotal moment where chemistry meets craftsmanship. It’s when the wine begins to take shape, absorbing the nuances we’ll later find in the glass - months or even years down the line.
Each sip carries the invisible imprint of that process: the silent work of yeasts, the choices of the winemaker, the rhythm of transformation. And it’s right here that the magic begins - long before the cork is pulled.