Wine tastes like fruit juice

Alcoholic fermentation - 10 terms how juice becomes wine

September is the main month of the grape harvest. This also means that the cellars are currently fermenting vigorously. Alcoholic fermentation is a miraculous process in which a sweet tasting juice is turned into a dry, aromatically complex and animating drink called wine.

Of course, this “basic wine” experiences a refinement and refinement during further expansion. There are also processes such as maturation in wooden barrels, fining or filtration. Nonetheless, alcoholic fermentation is the foundation of a wine. A lot can go well or wrong, which we will discuss below.

The 10 most important terms for alcoholic fermentation

During alcoholic fermentation, the sugar contained in the grape must is converted into alcohol and carbon dioxide. The carbon dioxide comes to the surface in the form of bubbles and escapes as fermentation gas. During this process, there can be a lot of bubbling. That is why alcoholic fermentation is sometimes referred to as stormy fermentation.

Normally, the must fermentation takes until almost all of the sugar has fermented. A dry-tasting wine is then made from a sweet juice. How, with what and in what such fermentation takes place, here are the ten most important terms.

1. Yeast strains

Yeast is essential for alcoholic fermentation to take place. The job of the yeast is to convert the sugar contained in the grape juice into alcohol and CO2.

There are innumerable strains of yeast; both desirable and undesirable for winemaking. Yeasts occur naturally in the vineyard as well as in the wine cellar. Nowadays they are also artificially propagated and produced in laboratories and used for alcoholic fermentation. More on this in points 2 and 3.

2. Spontaneous fermentation

With spontaneous fermentation, the must is fermented using natural types of yeast found on the berry skins and in the cellar. In this context, one also speaks of wild yeast, which converts sugar into alcohol.

Healthy grapes that are as natural as possible are essential for spontaneous fermentation. If, for example, grapes are sprayed a lot - which is still excessive in conventional viticulture - then hardly any yeast can form on the berry skins. A lack of (wild) yeast, in turn, means that fermentation will not start.

That is why it is often organic or biodynamic producers who rely on spontaneous fermentation.

Wooden barrels or clay amphorae can also prove to be advantageous, but not mandatory. In these containers, natural yeasts usually develop and maintain themselves better than in the more sterile stainless steel tanks.

With spontaneous fermentation, the winemaker gives up control to a certain extent. Because natural (wild) yeasts are always a mixture of different types of yeast. Which yeast strains will gain the upper hand in the fermentation process and how the wine will develop in terms of taste cannot be clearly foreseen.

3. Fermentation with pure yeasts

To avoid this uncertainty, most wineries rely on alcoholic fermentation with pure yeast. These are yeasts that have been artificially propagated in a laboratory.

The word “pure” already indicates that there is only one strain of yeast in the product and that it is free from bacteria and molds that may occur in natural yeasts.

Pure cultured yeasts are produced both as a dry powder and as a liquid. The powder is mixed with water and the pulpy substance is then added to the must. Fermentation begins immediately and takes place in a controlled manner, because the cultivated laboratory yeasts kill the wild yeasts.

If pure yeasts with a neutral flavor are used here, I personally don't see any problem.

On the other hand, I find the use of so-called aromatic yeasts, which support a desired aroma, questionable. Vintners can choose, for example, whether the later wine should taste milder or more piquant, rather like peach, banana or cassis. If you want to “pour pure wine” for consumers, you should stay away from aromatic yeasts.

4. Mash fermentation

Red wines are fermented on what is known as the mash. After the harvest, the red grapes are removed from the stems in the destemmer. The remaining mixture of berry peels, seeds and pulp is called mash.

The red pigments and the noble tannin are in the berry pods. The must draws the red color and tannin from the skins during the must fermentation. If the must of red grapes were fermented without a mash, you would get a white wine (keyword: Blanc de Noir). Because even with red grapes, the juice is light.

Mash fermentation usually takes place in open containers so that the carbon dioxide that is produced can escape.

Light red wines only ferment on the mash for three to four days. Heavy red wines, on the other hand, can stand on the mash for up to 30 days.

After the mash fermentation, the red wine is drawn from the mash into another container. What remains are the remains of the peel and pulp.

5. Alcoholic fermentation in white and rosé wines

In contrast to red wines, white wines are not fermented on the mash, i.e. without the skins. As soon as the grapes are harvested and reach the winery, they are pressed whole. The juice that runs off is pumped into fermentation tanks and cleared of dirt. After that, alcoholic fermentation can begin.

Like white wines, rosé wines are also fermented without skins. So that they can pull the reddish color and tannins out of the berry skins, rosés are left on the mash for two to twelve hours before fermentation. Then the must is pressed and fermented like a white wine.

For the sake of completeness, there are also the so-called orange wines. They are obtained from white grapes, but fermented on the mash like a red wine (see point 4). During the fermentation process, the must extracts the corresponding color from the white skins. The must gets its orange appearance.

6. Carbonic fermentation

This fermentation process is also known as carbonic acid maceration, intracellular fermentation or whole grape fermentation. The latter term shows what is meant: The fermentation tank is filled with whole, not destemmed grapes. The container is then closed and kept completely free of oxygen with the addition of CO2 protective gas.

Fermentation starts inside the berries without the action of yeast. In this way, the berries contain up to 2% alcohol by volume. Often times the berries burst open on their own and normal fermentation begins. Or the grapes are pressed after a few days and fermented further as juice.

What is the goal of this method? Carbonic acid or whole grape fermentation is used for red wines. Compared to classic mash fermentation (see point 4), it results in more fruity and less tannin-rich wines, which can usually be consumed more quickly. Since young, fruity red wines are currently in vogue, the process is being used more and more.

7. Temperature control

Whichever fermentation method a winemaker chooses, it is important that fermentation takes place at controlled temperatures.

If the fermentation is rampant, the temperature can rise to 37 degrees. What represents a healthy body temperature for us humans is rather incompatible with wine, because the must loses its aroma and taste in the process.

Nowadays fermentation tanks are mostly artificially cooled and the wine is fermented between 14 and 22 degrees. The cooler the temperature, the slower the fermentation yeasts multiply and the slower the must ferment. And the slower a must ferments, the more fragrances and aromas are retained.

8. Cold maceration

Cold maceration is not fermentation per se, but a method that precedes fermentation and is used by some wine producers.

Before the harvested grapes are processed further, the boxes are placed in a cooling chamber that is around four degrees cold for one to four days.

Since fermentation yeasts only start to work at a temperature of around 10 degrees, the grapes do not ferment in the cooling chamber. Instead, colors, flavors and tannins dissolve from the peel and go into the berry juice.

The aim of such a cold maceration is to intensify the fruit taste or the primary aroma of a wine. Red wines can also gain color intensity.

9. Fermentation flavors

The wine language differentiates between primary, secondary and tertiary aromas.

Primary aromas are those aromas that result from the grape. Mostly they are fruity and flowery. White wines from the Moscatel variety, for example, like to exude a tropical pineapple scent paired with white flowers.

Secondary aromas are those that result from alcoholic fermentation. These are often earthy, mineral, vegetable and / or pasty aromas that make a wine more complex.

Tertiary aromas arise during the aging process of a wine. This includes, for example, the expansion in barrique barrels and a long bottle storage. Flavors of vanilla, chocolate, dried fruit or even petroleum fall into this category.

Conclusion: The alcoholic fermentation brings with it so-called secondary aromas. So it is not just a juice that is converted into wine or sugar into alcohol. Rather, fermentation influences and shapes the aromas of the wine.

10. Stop fermentation

If everything goes as planned, the must will ferment automatically until almost all of the sugar is used up. Fully fermented wines contain less than one gram of residual sugar per liter. The wine then tastes bone dry. Not all wine lovers like that, after all, we live in a world full of sugar junkies.

Since many consumers like some residual sugar, many winemakers do not ferment their dry wines fully. After all, a wine is still considered dry, even with 9 grams of residual sugar, provided its total acid content is at least 7 g / l (or 8 grams of residual sugar with at least 6 g / l acid, etc.).

In order to obtain the desired level of residual sugar, the fermentation must of course be stopped. After all, the yeast will not stop converting the sugar into alcohol on its own.

There are various options for stopping fermentation:

a) The wine is pumped from the fermentation tank into another tank, separated from the yeasts and cooled down to five degrees in the new tank. If there is no yeast and if it is cold, fermentation will of course stop. At point 8 we already learned that yeasts only start to work at around 10 degrees.

b) Ferment the wine in closed tanks. If the carbon dioxide produced during alcoholic fermentation can no longer escape, fermentation is suppressed.

c) Fortified liqueur wines such as sherry are a special form: To stop fermentation, the wine is fortified with alcohol. From around 16 percent by volume, the yeasts die and fermentation stops.

Alcoholic fermentation - what can go wrong

Problems can arise especially with spontaneous fermentation (point 2), which is carried out by wild natural yeasts. Because sometimes the natural yeasts are not enough to get fermentation going or to keep it going. For example, if fermentation stops due to a lack of yeast, the wine will remain sweet.

With spontaneous fermentation it can also happen that the “good” yeasts die, the “bad” ones survive and the wine ends up smelling and tasting bad, for example like rotten eggs, sauerkraut or nail polish. From my own experience - I drink a lot of spontaneously fermented wines - I can say that such off-notes are extremely rare. And a little "spontaneous stinker" can even be stimulating.

If you ferment your wines spontaneously, you are still exposing yourself to a certain risk. Perhaps the winemaker will be rewarded for this by the miracle of alcoholic fermentation with exciting, extraordinary aromas. Conversely, pure yeasts that minimize risk contribute to the uniformity of wines and the taste of the wine.

And then there is the malolactic fermentation

Malolactic fermentation has nothing to do with alcoholic fermentation. Since we talk about fermentation all the time, it may still make sense to go into it briefly in conclusion.

Malolactic fermentation is also called malolactic fermentation (BSA). Long after the wine has fermented, malolactic fermentation begins naturally in spring.

In order for malolactic fermentation to start, the wine temperature must be over 20 degrees. Then bacteria present in the wine eat up the hard malic acid in the wine and produce soft lactic acid.

This process is particularly desirable for red wines because it makes the wine softer and more supple. In the case of white wines, on the other hand, malolactic fermentation is suppressed more often, for example in order to maintain the tangy and crunchy quality of white wine.


PS: We have forgotten one thing: that is Bottle fermentation in the production of sparkling wines. We have already explained how this works in an earlier article about the Spanish Cavas. Gladly for you to read or read on on our blog.