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The occurrence of succinic acid in wines

Charl Theron
In recent pressing seasons succinic acid has been puzzling South African winemakers. Usually the fixed acid content of wines decreases during and after fermentation concomitant with a decrease in the two most important fixed acids in grapes and wine, namely tartaric acid, as a result of tartrate precipitation, and malic acid, due to malolactic fermentation. However, winemakers occasionally saw the fixed acid content increase during and after fermentation, which complicates the calculation with regard to acid corrections. It looks as though the formation of succinic acid may be responsible for the problem. Comprehensive research into this matter has been done in Australia, the findings of which are summarised in this article.
The increase in the total acid content analysis of wines is sometimes ascribed to analytical problems. For example, it may occur as a result of inefficient sampling or defective laboratory equipment.
Succinic acid is encountered in wine grapes in minute quantities only. It is a normal byproduct of alcoholic fermentation and the most important non-volatile acid that is formed during alcoholic fermentation. Occasionally malic acid is formed at the same time, but succinic acid is formed in higher concentrations. A watery solution of succinic acid has a salty, bitter taste that is also noticeable on the aftertaste.
From 1991 to 2003 the succinic acid content of 93 Australian red wines and 45 Australian white wines was determined by the Australian Wine Research Institute and the results may be summarised as follows:

The content in red wines ranged from not noticeable to 2,6 g/l with an average content of 1,2 g/l. Qualities of up to 3,0 g/l did occur in red wines, however.
The content in white wines ranged from 0,1 to 1,6 g/l with an average content of 0,6 g/l.
The average content of red wines is twice that of white wines.
A high percentage (63%) of the red wine content ranged from 0,8 to 1,6 g/l. If one takes into account that 1 g/l succinic acid is the equivalent of 1,3 g/l tartaric acid, the latter quantities mean that 1,0 to 2,1 g/l of the total titratable acid is tartaric acid.

Succinic acid may be formed by yeasts from sugar or amino acids. The formation thereof will be determined by the growth conditions and the available sources of nitrogen to which the yeasts are exposed. The formation thereof is influenced by various factors:

Yeast strains differ considerably as regards the concentrations of succinic acid that have been formed.
It looks as though higher fermentation temperatures of up to 30 degrees C might benefit the formation of succinic acid by mesophyl yeast strains, while cryotolerant yeast strains form the most succinic acid at 18 to 20 degrees C.
High pH-values benefit the formation of succinic acid.
Aeration promotes the formation of succinic acid.
Increased formation of succinic acid will occur with increasing nitrogen, glutamate and aspartate content.
Increased levels of the vitamins thiamin, biotine and pantothenate may result in increased formation of succinic acid.
Musts with a high sugar content may result in increased formation of succinic acid.
Lower percentages of solid matter in musts will result in decreased formation of succinic acid.
Apparently different red wine cultivars (Shiraz, Cabernet Sauvignon, Merlot, Sangiovese, Petit Verdot, Ruby Cabernet and Grenache) do not have an influence on the succinic acid content of wine, but in the case of white wines (Chardonnay, Riesling, Sémillon, Marsanne, Trebbiano and Verdelho) the different cultivars do play a role. It looks as though the highest succinic acid content occurs in Chardonnay. This could on the other hand be ascribed to vinification practices, in view of the fact that wood fermented Chardonnay wines contain more solids and are usually more exposed to air.
Differences from one vintage to the next may occur seeing that conditions causing high nitrogen content or low potassium content in grapes may result in higher succinic acid content in wines.

Under certain conditions it may be beneficial if succinic acid is formed during fermentation so as to cause an increase in the total acid content of wines. This is especially so in cases where the pH- and K-quality of wines are high, while the tartaric acid content of the wine is low.
The potential formation of succinic acid can therefore be used to good effect by winemakers if managed correctly.
Reference:
Coulter, A D, Godden, P W & Pretorius, I S, 2004. Succinic acid. Wine Industry Journal 19(6): 16 - 25.

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