How long does the fermentation of a wine take?

Fermentation is undoubtedly one of the most important stages in winemaking. It's the turning point where the sweet must is transformed into a complex and vibrant beverage. To novices, it may seem like a simple biological process, but for the winemaker, it's a delicate and precise task.

Hence the big question many ask when they begin to explore the world of wine: how long does wine fermentation take? The answer isn't simple, as the time varies drastically from a few days to several months, depending on the grape, the desired style, and the winemaker's decisions.

In this article, we'll not only discuss exact figures, but also explore the main phases of the aging process and discover how this duration directly affects the flavor, aroma, and final characteristics you'll enjoy in every glass. Keep reading!

What is wine fermentation and what is it used for?

Fermentation is a natural biochemical transformation process that occurs in grape must. Simply put, it's the moment when the sugars present in grape juice are converted into ethyl alcohol and carbon dioxide (CO2) through the action of yeast.

It is a vital process: without fermentation, we would not have wine, but only grape juice.

What is the purpose of fermentation?

The main function of this process is twofold:

1. It converts the natural sugar of the grape into alcohol, which defines the alcoholic strength of the final wine.
2. As the yeasts work, they release a wide range of secondary compounds responsible for the wine's characteristic aromas and flavors. Controlling the duration and temperature at this stage allows the winemaker to shape the wine into the desired style, maximizing color and tannin extraction in reds and preserving freshness in whites.

The 2 key phases in fermentation

When we talk about wine fermentation, we generally refer to two distinct biochemical processes that can occur sequentially. Both are fundamental to the structure and sensory profile of the wine.

Alcoholic fermentation

Alcoholic fermentation is the main and mandatory phase, where the magic really happens. It consists of the action of yeasts (essential microorganisms, natural or selected) that metabolize the sugars present in the grape must (glucose and fructose).

The result is the production of ethyl alcohol, carbon dioxide (CO2) and, as a byproduct, a wide variety of compounds that define the primary aromas of wine.

The duration of the FA depends on the temperature controlled by the winemaker:

• In red wines, high temperatures (25ºC to 30ºC) are sought for rapid extraction, lasting between 5 and 14 days.
• In white and rosé wines , a slow process at low temperature (14ºC to 20ºC) is preferred to preserve freshness and delicate aromas, which extends the process to 15 or even 30 days.

Malolactic fermentation

Maltodextrin (MLF) is a secondary fermentation process that is almost always pursued in red wines, but is optional in white wines (except for specific styles). Unlike alcoholic fermentation, this phase is driven by lactic acid bacteria, not yeasts. Its function is to convert malic acid (hard, similar to that of a green apple) into lactic acid (smooth and creamy, similar to that of milk). This change reduces the overall acidity of the wine and adds aromatic complexity, often contributing buttery or dairy notes. MLF is much slower and more difficult to predict than alcoholic fermentation, and can last from three weeks to three months or more, depending on the winery conditions and temperature.

Factors that influence the duration of fermentation

The duration of alcoholic fermentation (AF) and malolactic fermentation (MLF) is never fixed. It depends on a series of technical decisions made by the winemaker and the natural conditions of the grapes. The three most determining factors are:

• Temperature : This is the most crucial factor. Yeasts (and lactic acid bacteria) are very sensitive to temperature. If the temperature is high, the process accelerates dramatically, often completing in less than a week. If the temperature is low, the activity of the microorganisms slows down, resulting in controlled fermentations that can last three or four weeks. The key is control: if the temperature gets too high, the yeasts can die, causing the fermentation to stop.
• Type of wine :
  • Red wines : They generally ferment faster (FA) due to the high temperatures required to extract color and tannins from the grape skins. Furthermore, they almost always undergo malolactic fermentation (MLF), lengthening the total time in the winery.
  • Fresh white and rosé wines : These are cold-fermented to preserve varietal aromas and acidity, which means slower fermentation processes. Malolactic fermentation (MLF) is often avoided to maintain that fresh, vibrant mouthfeel.
  • Sweet wines : To make sweet wines, fermentation is intentionally stopped, leaving a residual amount of sugar. This involves complete control over the process and the use of techniques to "kill" the yeasts before they finish their work.
• Sugar concentration : A high initial sugar concentration in the wort (which will result in a potentially high alcohol content) can slow down fermentation. As the alcohol level rises, it becomes toxic to the yeast, hindering its work.
• Yeast used : The choice of yeast is vital. Some selected yeasts are very potent and fast, while wild yeasts (indigenous, native to the vineyard) tend to be slower and contribute to greater aromatic complexity, but carry a risk of a more erratic process.

Frequently Asked Questions

How does the duration of fermentation affect the final flavor?

The duration of fermentation is fundamental to the sensory profile of wine. A slow fermentation at low temperatures (typical of many quality white wines) allows the yeasts to work at a leisurely pace, generating esters that enhance fruity, floral, and delicate aromas. On the other hand, a faster and warmer process (typical of red wines) favors greater extraction of color, tannins, and structure from the grape skins, resulting in more powerful and longer-lasting wines. Controlled time is, therefore, the winemaker's tool for shaping the desired aromatic style.

How long does Malolactic Fermentation (MLF) last?

Malolactic fermentation (MLF) is notoriously slower and more unpredictable than alcoholic fermentation. While it can last as little as three weeks under ideal temperature conditions (around 20°C), it commonly extends over several months, especially in cellars with cooler ambient temperatures. Lactic acid bacteria are sensitive and often require rigorous temperature control to ensure the process is completed successfully and without the risk of aromatic deviations.

What happens if the fermentation is not done correctly?

A poorly executed fermentation can ruin a batch of wine. The most common problem is arrested fermentation, where the yeast dies (often due to excessive temperature or lack of nutrients) before it has consumed all the sugar. This leaves an unstable wine with unwanted residual sugar, which can be prone to contamination. Other risks include loss of aromas or volatile wines.