How to Tell if Wine is Fermenting

Last Updated on August 1st, 2023

Reader Disclosure Disclosure: We may earn commissions for purchases made through links on our site. Learn more on our about us page.

Natural fermentation occurs when a piece of fruit or sugar has time to be converted into alcohol molecules. The fermentation is usually taken on by a microorganism, which releases carbon dioxide molecules as a by-product along with probiotics.


What are the signs of fermentation?

When observing the wine ferment, it begins with little patches of fine bubbles on the surface of the liquid. After those bubbles appear, it leads to a thick layer of bubbles that covers the surface of the aging wine. 

Carbon dioxide will be released naturally but must be let out of the airlock to allow fresh oxygen to the yeast. Here is a quick list to tell if your wine is fermenting:


  • Bubbles
  • Escaping carbon dioxide
  • Swirling particles inside the wine
  • Krausen forms a light layer of bubbles on the surface


How to tell if my wine is still fermenting or just degassing?

Degassing, for those that do not know, is the process of removing suspended carbon dioxide left over from fermentation, according to the winemaker’s academy. 

The process is not always required, but when carbon dioxide has blanketed the liquid, simple aeration of the mixture will jumpstart the fermentation process. 

On another note, degassing will take place for only three to four months during the natural fermentation process.


How does the fermentation process work?

In the case of winemaking, this takes place during the aging process. Before modern fermentation, vineyards used natural fermentation techniques. None of which reacted precisely the same; no two vintages are alike when made this way.

In the 17th and 19th centuries, microbiologists found the catalyst to the whole fermentation process was a live organism, yeast. 

Another discovery by Louis Pasteur was “respiration without air,” this was different from the natural method because lactic acid and bacteria take the place of yeast.

In the 1950s, “commercial” or “cultured” yeast first began to appear and took off as the favorite method of fermenting alcohol. Saccharomyces Cerevisiae is the specific species of yeast used for this process, but also in bread.


Can you open the lid to check on the fermentation process?

Though not recommended, opening the airlock on a barrel will allow oxygen and other compounds in the air to mix into the vintage. Though, when degassing is required, one must open the lid.

Or use what is called “the whip.” This tool is perfectly shaped for agitating and releasing carbon dioxide without oxidizing or splashing the wine.


How can you tell if fermentation is done?

According to multiple winemakers, the natural processes of fermentation and the winemaking process, in general, were carried out by guy and heart’s instinct. There are two stages of fermentation.

Primary fermentation is where most alcohol, about seventy percent, is created within three to five days. Since we’ve covered the first fermentation process, let us get to secondary fermentation.

During this second stage, the final thirty percent of the alcohol production occurs. The foam will dissipate, and tiny bubbles will appear on the surface. To be clear, these two stages of fermentation are not independent of one another.


Final Thoughts

Fermentation is a natural process that converts starches and sugars into alcohol and various other by-products. This process can then be refined to make beverages like wine. To be sure that the wine is fermenting, check for bubbles.