VinoLoverBy nature, all wines are acidic because they come from an acidic raw material, which is why it is known that a wine without acidity is a wine without life. From the point of view of preservation, smell and taste, acidity is essential.
During the ripening process, the grape contains most of the acids that take part in the vegetative cycles, as well as in other reactions carried out by the plant.
Tartaric acid and malic acid account for 90% of all the acids in the grape, which are synthesised in the leaves and in the bunches themselves
Volatile acidity is the proportion of vinegar present in the wine, a completely undesirable but unavoidable factor. Winemakers strive to keep it as low as possible, so today we will take a closer look at volatile acidity and what it represents in winemaking.
Types of acid in wine
There are 5 types of acid present in wine. Next, we will see what each type of acid contributes to the wine:
- Tartaric acid: in the winemaking process, low temperatures can cause the formation of calcium and potassium salt crystals, which are completely harmless and can be found in some bottles, indicating that the wine was not correctly stabilised. If this acid is very abundant, it presents a certain hardness when drunk.
- Malic acid: this acid is very important for the life and preservation of some wines. It disappears due to the action of lactic bacteria. Its major quantity is not concentrated in the wine but in the must.
- Citric acid: this acid is not very abundant in grapes. When fermented by bacteria, it disappears slowly.
- Succinic acid: this acid is part of one of the elements that give fermented beverages their characteristic flavour. It is produced during the fermentation process
- Lactic acid: it is derived from malic acid, but is much milder than malic acid. This acid is produced during fermentation by lactic acid bacteria (after alcoholic fermentation) in the so-called malolactic fermentation. This acid is found to a greater extent in red wines, as white wines generally do not undergo malolactic fermentation
In a fixed and constant way, these acids are part of the acidity of the wines, but there is another acid that is responsible for the volatile acidity of the wine, and that is acetic acid, which can be easily detected by smell. This acid is the natural result of fermentation and enhances malolactic fermentation slightly
What is volatile acidity?
Volatile acidity is part of the total acidity of the wine. It is made up of the primary acids that are present in the grape must (tartaric and malic) and the secondary acids that are generated during the fermentation process (malic, succinic, acetic). Acidity is also added by some gases and dissolved substances such as sulphur dioxide, carbon dioxide and sulphites, which are added as preservatives
All these acids give the wine the necessary acidity for a better preservation, but in order to obtain a balanced product, it is necessary that they have the right amount in relation to the other components.
The volatile acidity is in charge of calculating the acetic acid of a wine. It is said that a wine is pungent when its volatile acidity is above 1g/l and its aroma resembles varnish or vinegar; this can be caused by excessive ageing in oak barrels or alteration.
On the palate, the malic acid gives an acidic and fresh sensation. Due to malolactic fermentation, red wines have less acidity than white or rosé wines.
What are the ways in which acetic acid is formed?
Acetic acid is volatile, and is found in the distillate, which is why it is called volatile acidity. Now we will see how it is formed:
- In alcoholic fermentation: due to the fermentation of sugars, acetic acid is a by-product, so we can find it in all wines.
- In malolactic fermentation: it comes mainly from the fermentation of citric acid and pentoses.
- Bacterial alterations: when acetic bacteria come into contact with air, they oxidise the alcohol and turn it into acetic acid.
As long as the volatile acidity does not exceed 0.55 or 0.60 gr/litre, the taste of the wine will not be affected too much, but it must be clear that the quality of a wine is much higher when its volatile acidity is lower. Contrary to what many people think, acetic acid does not give it a better bouquet or the smell of mincemeat, which is due to ethyl acetate.
In white and rosé wines a correct check should be 0.2 and in red wines 0.3 or 0.4. On the contrary, an incorrect vinification gives a value of 0.5 and a wine starts to show a negative sensation when the value is 0.9.
Ageing does not necessarily make this value go up. Moreover, you should know that there is no treatment that can lower these values.
García Tena method to determine the volatile acid in wine
By means of a fractional distillation plus a titration with 0.02 N sodium hydroxide and a 1% phenolphthalein indicator, the Gracia Tena group can calculate the volatile acidity of wine
The procedure for the calculation is as follows
- Place 11 ml of wine without carbon dioxidein the distillation flask and connect the distillation apparatus.
- Then place the measuring cylinder with 5.1 ml in the coolant outlet and distil until full.
- Immediately replace with the 3.2 ml graduated cylinder. Collect the 3.2 ml at the end of the distillation in this second cylinder.
- Pour the 3.2 ml from the second cylinder into an erlenmeyer flask, add a few drops of phenlphthalein (1%) and titrate with 0.02 M sodium hydroxide solution.
Mark the end point when the indicator turns pink. The volume of base used is noted and the following calculation is made:
Volatile acidity (g/L)= 0,366xV
Volatile acidity is normally between 0.20 and 0.70, depending on the wine and the winemaking process.
Carbon dioxide provides acidity, so it is important to eliminate it so that it does not cause an alteration in the results. For this purpose, there are different methods, such as vacuum aspiration, which serves to degas the wine before placing it in the distillation flask.
As we have seen, volatile acidity is a by-product produced by yeasts in the alcoholic fermentation process, which should be removed from the wine after fermentation. This can be done in its free form, if its concentration is not too high, which can be achieved with good aeration. Raising the temperature of the wine also facilitates its removal.
Volatile acidity can be easily perceived from 0.8 g/L to 0.9 g/L, depending on the taster’s palate.
Precautions to be taken with volatile acidity
With the volatile acidity there are certain things to take into account in order to achieve the best quality wine, among which we can highlight
- Sulphite must be removed in time to avoid micro-organisms that produce it.
- Avoid oxidation of the skins during fermentation.
- Ensure that the musts have a good pH level.
- Watch for oxidation once the wine is already fermented and keep it in anaerobic conditions
VinoLover
Claudio Comella
