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How does wine fermentation work?

Views: 16     Author: Site Editor     Publish Time: 2024-03-07      Origin: Site

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Post summary

wine fermentation process

 1.1 Timing of harvest

 1.2Harvesting methods

  1.2.1Manual harvesting  1.2.2mechanical harvesting

2.Grape sorting



 3.2Crushing Methods

  3.2.1Mechanical Crushers

  3.2.2Pneumatic Presses

 3.3Skin Contact (Maceration)

 3.4Cold Soaking (optional)

 3.5Sulfur Dioxide Addition (opional)

 3.6Juice Collection

4.Wine fermentation

 4.1Yeast Selection

  4.1.1Natural Fermentation

  4.1.2Inoculated Fermentation

 4.2Fermentation Vesse Selction

  4.2.1 Stainless Steel Tanks

  4.2.2 Oak Barrels

  4.2.3 Concrete Tanks

 4.3Temperature Control

  4.3.1 Cool Fermentation (for white wines)

  4.3.2Warm Fermentation (for red wines)

 4.4Fermentation Phases

  4.4.1Lag Phase

  4.4.2Exponential Growth Phase

  4.4.3Stationary Phase

  4.4.4Decline Phase

 4.5Monitoring and Adjustments

  4.5.1Sugar Levels


  4.5.3pH and Acidity

 4.6Cap Management (for red wines)

  4.6.1Punching Down

  4.6.2Pumping Over

4.7Completion of Alcoholic Fermentation

  4.7.1Testing for Dryness

  4.7.2Sensory Evaluation

4.8Malolactic Fermentation (optional)

5.Racking and Aging

6.Clarification and Filtration


Wine fermentation is a natural and complex process that transforms grape juice into wine. The key player in this transformation is yeast, specifically Saccharomyces cerevisiae, although there are other wild yeast strains that can contribute as well. Here's a more detailed breakdown of the wine fermentation process:


Grapes are harvested when they are fully ripened. The timing of the harvest is crucial because it affects the sugar content, acidity, and overall flavor profile of the grapes.


1.1 Timing of harvest: 

Grapes are monitored throughout the growing season until appropriate harvest conditions are met. Depending on which hemisphere you're in, this time frame flips completely. Many wineries rely more on actual grape conditions than any season. Different styles of wine have different levels of acidity and sugar content requirements for grapes, and wineries must pay close attention and only pick the grapes when they meet the required conditions.

Grapes are harvested when fully ripe. Harvest time is critical as it affects the sugar content, acidity and overall flavor of the grapes.

1.2Harvesting methods: 

mainly divided into manual harvesting and mechanical harvesting

 1.2.1Manual harvesting

The traditional way of picking grapes, by hand, produces the highest quality grapes. The staff is trained to specifically select grapes to create the desired style of wine. This method is much slower than mechanical harvesting but produces the best grapes in terms of taste and condition.

 1.2.2mechanical harvesting

Mechanical harvesting is the more popular harvesting option, using advanced machinery to collect the grapes. Large trucks ride over the grape trellises and use vibrations to remove the bunches. The grapes then fall onto a collection plate and then onto a conveyor belt or collection bin.

This method is much more efficient than hand picking, but often damages or bruises the grapes.

2.Grape sorting

Once the desired grapes have been collected, a quality control process must be completed to select the good grapes from those that may be unripe, damaged, or otherwise unsuitable for the desired wine style.

Similar to harvesting, both mechanical and manual options are available, but most advanced wineries use a mixture of the two and rely heavily on machinery.

Grape sorting


Crushing is a crucial step in winemaking that involves breaking open the grape berries to release the juice, which will eventually ferment into wine. This process allows the winemaker to extract flavors, colors, and tannins from the grape skins, seeds, and pulp. Here are more details about the crushing process:



Before crushing, the harvested grapes often undergo destemming. This step removes the stems from the grape clusters, as the stems can contribute bitter flavors to the wine. Destemming can be done mechanically or by hand, depending on the winery's equipment and preferences.

3.2Crushing Methods:

 3.2.1Mechanical Crushers: 

Many wineries use mechanical crushers to efficiently break open the grape berries. These machines can vary in design but generally involve a rotating cylinder or rollers that exert pressure on the grapes, causing them to burst and release their juice.

 3.2.2Pneumatic Presses: 

In some cases, especially for white wines or delicate grape varieties, winemakers use pneumatic presses instead of crushers. These presses gently press the grapes to extract juice without macerating the skins excessively, preserving the desired qualities.

3.3Skin Contact (Maceration):

After crushing, the grape skins, seeds, and pulp are in contact with the juice in a process called maceration. This contact allows compounds such as phenols, tannins, and pigments to leach into the juice, influencing the wine's flavor, color, and structure.

3.4Cold Soaking (optional):

Some winemakers choose to implement a cold soak before fermentation. This involves chilling the crushed grapes to extract additional color and flavor from the skins before fermentation begins. Cold soaking can enhance the complexity of the resulting wine.

3.5Sulfur Dioxide Addition (optional): 

Some winemakers add sulfur dioxide to the crushed grapes to prevent oxidation and inhibit the growth of undesirable microorganisms. Sulfur dioxide also helps preserve the freshness and color of the grape juice.

3.6Juice Collection:

The collected juice is then transferred to fermentation vessels, such as stainless steel tanks or oak barrels, where the fermentation process will take place.

4.Wine fermentation

Wine fermentation is a complex biochemical process that involves the conversion of sugars in grape juice into alcohol and carbon dioxide by yeast. Here are more details about the wine fermentation process:

Wine fermentation

4.1Yeast Selection:

 4.1.1Natural Fermentation: 

Wild yeast strains present on grape skins or in the winery environment can initiate fermentation. However, this method can be unpredictable and may result in variations in flavor and fermentation speed.

 4.1.2Inoculated Fermentation: 

Many winemakers prefer to use selected yeast strains, often Saccharomyces cerevisiae, to ensure a controlled and consistent fermentation. Commercial yeast strains are chosen for their ability to produce specific flavors and aromas.

4.2Fermentation Vesse Selction:

 4.2.1 Stainless Steel Tanks: 

Commonly used for their non-reactive properties and ease of cleaning.

 4.2.2 Oak Barrels: 

Used for certain styles of wine, as they can impart unique flavors and aromas to the wine.

 4.2.3 Concrete Tanks, Wooden Vats, or Amphorae: 

Some winemakers opt for these vessels to influence the fermentation process.

4.3Temperature Control:

 4.3.1 Cool Fermentation (for white wines): 

Temperatures around 45-60°F (7-15°C) are often used to preserve the delicate aromas and flavors of white wines.

 4.3.2Warm Fermentation (for red wines): 

Temperatures around 70-85°F (21-29°C) are common for red wines to extract color and tannins.

4.4Fermentation Phases:

 4.4.1Lag Phase: 

Yeast acclimates to its environment.

 4.4.2Exponential Growth Phase: 

Yeast cells multiply rapidly.

 4.4.3Stationary Phase: 

Yeast growth slows as nutrients are depleted.

 4.4.4Decline Phase: 

Some yeast cells die off, and fermentation slows down.

4.5Monitoring and Adjustments:

 4.5.1Sugar Levels: 

Winemakers monitor sugar levels using tools like a hydrometer or refractometer to track the progression of fermentation.


Control is crucial to maintain the desired fermentation rate.

 4.5.3pH and Acidity:

Monitoring acidity levels ensures a balanced wine.

4.6Cap Management (for red wines):

 4.6.1Punching Down: 

Submerging the grape skins into the fermenting liquid to extract color, tannins, and flavor.

 4.6.2Pumping Over: 

Circulating the fermenting liquid over the grape cap to achieve similar extraction.

4.7Completion of Alcoholic Fermentation:

 4.7.1Testing for Dryness: 

Winemakers may test the wine for dryness by checking if all sugars have been converted into alcohol. This is done through sugar analysis or tasting.

 4.7.2Sensory Evaluation: 

Winemakers assess the wine's sensory characteristics to determine if it meets their desired profile.

4.8Malolactic Fermentation (optional):

Bacterial Conversion: Malic acid is converted into lactic acid by lactic acid bacteria, providing a smoother taste.

Conditions: Winemakers may choose to induce or prevent malolactic fermentation based on the wine style.

5. Racking and Aging: 

Once fermentation is complete, the wine may be separated from the solids through a process called racking. The wine is then transferred to barrels or tanks for aging, allowing it to develop its flavors and aromas.

6.Clarification and Filtration: 

To remove any remaining particles and sediment, the wine may undergo clarification and filtration processes.


Finally, the wine is bottled for distribution and consumption. Some wines continue to evolve in the bottle over time, and aging can play a significant role in the final flavor profile.

It's important to note that winemaking is a complex and nuanced process, and variations in techniques, grape varieties, and regional practices contribute to the diverse world of wines.

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