Wine Fermentation: What Is It and What Types Are There?

Simply put, we can say that alcoholic fermentation is the part of the winemaking process that turns the natural sugars in the grapes into ethyl alcohol. Our fermentation process always starts with destemming the grapes (red and white) to get rid of any leaves and stems.

Then they are pressed, for white grapes, and immediately filtered to separate the must from the skins and seeds so they won’t affect the colour of the finished wine. After that, alcoholic fermentation takes place when the sugar in the must is transformed into alcohol in stainless-steel tanks at a controlled temperature (14 °C-16 °C).

For red wines, the process is similar but the grape skins are left in the must while it ferments in the stainless-steel tanks to extract all the colour compounds, which give these wines their characteristic hue.

The big mystery is rosé wine, which is somewhere between a red and a white. Meaning we use 100% red grapes but, during fermentation, the skins are only left in the must long enough to give it that pink tone.

This process of turning sugar into ethyl alcohol is done by yeast, either the yeast naturally present on the grapes or selected yeast, which is grown in a lab. Yeast turns the natural sugars from the grapes into ethanol and carbon dioxide. In this case, fermentation doesn’t only create alcohol, it also contributes new aromas and flavours to the wine.

Selected yeast is a component added by oenologists during wine fermentation and there are many types. For example, the natural yeast on the grape skins and yeasts grown in a lab.

Sugar is another essential component for wine fermentation. The more sugar, the more alcohol the yeast will produce. However, too much sugar is also bad because it is harder for the yeast to turn it into ethanol and can halt the fermentation, affecting the aromas and flavours of the wine.

Fermentation temperature is another factor that has to be carefully monitored. Depending on this temperature, you get different nuances. Normally, red wine is fermented at a higher temperature than white wine.

Most wines, whether white, rosé or red, are fermented in large stainless-steel tanks, which offer the best hygiene and temperature conditions. However, there are more and more whites and reds that have been fermented in oak barrels. These barrels make the wine buttery and impart the aromas and flavours of the wood.

Many wines undergo more than one fermentation. While the primary fermentation creates alcohol and other compounds that improve the taste, some wines also need a secondary fermentation.

Alcoholic fermentation

As we said earlier, in alcoholic fermentation, yeast on the grapes turns sugars into alcohol naturally. The yeast that carries out the fermentation process is a micro-organism that break down any organic material.

(h3)Malolactic fermentation

Malolactic fermentation is the process in which malic acid, naturally present in grape must, is converted to lactic acid. In red wines, this normally takes place after alcoholic fermentation. This malic acid is what gives some wines their acidity and freshness, like white wines for example.

Bottle fermentation

Sparkling wines have another fermentation process after they are bottled. The oenologists add a combination of sugar and yeast to the wine, which generates carbon dioxide and the characteristic bubbles found in this type of wine.

Carbonic maceration

Also known as whole-bunch fermentation, in this process the grapes are fermented whole. This process is typically used in La Rioja to make young wines.

Destemmed fermentation

In this case, the stems are removed before fermentation. This process tends to be used to avoid any defects in the wine, like grassy notes.