Written by: Tim Edison

Updated: November 17, 2023

How is Wine Made Alcoholic? [The Fruit to Alcohol Process]

pouring wine into glass

It's a magical process that's completely natural, but how does it happen? How does fruit or fruit juice become the alcoholic drink that we love so much?

In today's winemaking guide, we break down the process into the key steps that make fruit into wine!

From Grapes to Wine: The Process

A study in 2015, published in the Journal of Wine Economics actually found the alcohol content in many wines to be higher than stated on the label.

Their findings showed that around 60% of bottles in the study contained alcohol contents of 0.42% more than that was stated on the label.

But, where does this alcohol come from? How does wine become alcohol in the first place?


A freshly ripe organic grapefruit contains high amounts of sugar. The environmental conditions determine the amount of sugar in any fruit.

For instance, grapes grown under moderately warm weather may contain more sugar than fruits grown in cold areas.

It is also important to note that the higher the amount of sugar, the higher the levels of alcohol can be created.

The process of fermentation creates alcohol in drinks. It takes sugars and transforms them into alcohol (and carbon dioxide) with the help of yeast.

Non-alcoholic wines can be made too, but they usually go through the fermentation process (as it creates some of the amazing flavors and aromas) then have the alcohol removed.

While there exists another technique – capitalization whereby sugar is added to the grape juice during fermentation to boost the alcohol levels, natural wine is fermented with its own sugars.

This technique was borrowed from Jean Antoine who is said to have invented it. In general terms, the yeast consumes all the sugar in the juice and converts it into half carbon dioxide gas and alcohol.

For example, if you happened to have five gallons of juice that had ten pounds of sugar and you fermented all the sugars with the yeast, you will end up with five gallons of grape juice with roughly five pounds of alcohol in it (alcoholic content can be measured accurately using a device called a hydrometer).


Yeast is the fundamental component in fermentation.

Sometimes wines are mostly defined by the yeast used.

Yeast varies widely from one place to another and has a tangible contribution to the aromas of the finished product. Yeasts in certain parts of the world give the wines their character.

Compactly grown grapes have very little or no yeast at all on their skin. If the winemaker suspects there are remnants of yeast on the vines, he or she kills them with sulphur dioxide and reseeds the grapes with an individual strain of commercially processed yeast. While this is a conventional method of wine fermentation, natural wines are fermented only with the wild yeast present to its terroir.

Wines fermented with commercial yeasts have less personality and a lesser expression of their terroir. The apparent reason why they taste similar. These types of wines are also less complex, less tasty as wild yeasts present on any organic grape contributes something unique to the end product.

Artificial yeast such as (Saccharomyces cerevisiae, in liquid or dried form) is usually added to facilitate and control the process of fermentation. They typically work by consuming all the sugar present in the juice to produce alcohol and carbon dioxide along with other alcohol esters which play a significant role in the flavors and aromas of the wines.


The process of fermentation brings forth the secondary flavor and aroma of the wine. It is through this process that the alcoholic beverage is produced.

The speed of fermentation as well as the temperature and oxygen level are vital determinants of the wine. The process usually takes place in two stages the primary and the secondary level.

The biological term for primary fermentation is aerobic fermentation. In this stage, fermentation involves air. Oxygen plays a dominant task in multiplying the yeast cells. The multiplication of the cells takes place in the first few days and alcohol is also produced, but a significant amount of yeast is engaged in reproducing itself.

The secondary fermentation also known as anaerobic fermentation takes place without the presence of oxygen.

The yeast cells that were multiplying in the first stage also get useful in alcohol formation. This second part of fermentation usually takes longer than the first part depending on the amount of sugars and nutrients available. The second fermentation stage is slower because there is less activity due to lack of oxygen. 

Other General Factors


Climate change can partially be blamed for the high alcohol content in wines today. The hot climate heats up the fruits thus increasing the levels of sugars in them which is later converted to alcohol.

There's also a familiar concept by wine enthusiasts that higher alcohol content in wines is healthier than the higher acidity and other austere visions of the past generations. The added sugar also contributes to the high levels of alcohol during fermentation.


Another unique factor that contributes to the amount of alcohol in wine is temperature. This variable doesn't matter only when storing wine. It also catalyzes the process of fermentation. 

If the temperature is too low, the yeast in the primary fermentation may not multiply as it will not be invigorated enough to ferment the juice. It will only remain in the juice, dormant.

If the temperature is too high, the yeast will perform great as far as fermenting is concerned but the flavor of the wine will be affected.

The taste may suffer primarily because of low acidity and production of unwanted enzymes that influence to the growth of microorganisms. Therefore, it is quite indispensable to have the correct temperature during fermentation. 

Final Thoughts

A point to take home is that a 3% percentage increase in sugar concentration is a 3% increase in alcohol. Sugar is the prime component of wine. It's what determines the amount of alcohol in wine.

So, the bottom line: how does wine become alcoholic? Simple, through the fermentation of the sugars in the grape juice by the yeast!

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About the Author Tim Edison

Tim started Wine Turtle way back in 2015.
These days he contributes to Wine Turtle (and other renowned wine publications) while continuing his wine education.
Tim's wine of the month is the Coates & Seely Reserve Brut NV (from Hampshire, England).

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