One of the most important factors influencing the overall taste of a white wine, acidity levels, are key to the wine making process. But while the language used to describe acidity in wine can appear disarmingly complex, a little knowledge of this area can be important in deepening our understanding and enjoyment of wine.
In a nutshell, acidity affects a wine’s balance. Too acidic and a white wine will taste overly tart and bitter. Not acidic enough and a wine will taste ‘flat’, lacking depth and flavour. A wine is said to be ‘well-balanced’ when the acidity is in perfect harmony with the sweetness of the wine. The development of a wine’s acidity begins with the grape itself. As the fruit matures, so its acidity changes and this will eventually impact on the balance of the wine itself. However, acidity levels can be easily altered by wine makers, to create a pleasingly well-balanced wine.
Now, pay attention, here comes the science part. There are several acids to be found in wine grapes – the most important of which are tartaric acid and malic acid. Potassium hydrogen tartrate and potassium hydrogen malate, both also present in red and white wine, are derivatives of these two key acids. The amount of tartaric and malic acids found in white grapes varies according to grape varietals and the region in which the grapes are grown. This is one factor that determines the difference in taste between wines grown from the same varietal in different regions. For example, a white wine made from Chardonnay grapes grown in California will taste very different to a Chardonnay wine made from grapes grown in the Burgundy region of France, where grapes typically have lower levels of malic acid.
Both of these acid types are classed as non-volatile – in other words, they will not evaporate when the wine is heated. They are therefore markedly distinct from the acetic acids also present in wine, which are volatile and do evaporate when the liquid is heated. These acetic acids are in effect vinegar and high levels will lead to a white wine that tastes unpleasant. It is with good reason that some very bad white wines are described as ‘vinegar’! As a general rule, the level of acetic acid in a wine should not exceed 0.06 per cent and not fall below 0.03 per cent.
Both tartaric and malic acids are produced by wine grapes as they mature. Warmer wine regions tend to produce white wine grapes that are less acidic than those of cooler regions, as much of the acidity is lost through the plant’s respiration process. The acids present in both red and white wine need to be balanced with the wine’s level of sugar. Here, the reverse of the acidity process is true – the grapes of very warm climates will be higher in sugar than those of cooler climates and the high sugar content together with low acidity creates grapes that are very different in taste to those of cool wine producing regions such as the Chablis region of France. In very cool regions, a lack of warm sunshine can result in grapes that lack the sweetness to create good wines. To avoid overly acidic white wine, it is considered acceptable for winemakers to introduce some sugar during the wine making process if it has been a particularly cool year. In warmer climates, the reverse is true – the addition of sugar is considered unacceptable, but winemakers’ associations allow the introduction of tartaric acids to balance out wines that would otherwise be overly sweet.
When it comes to adjusting the acidity of a wine, malolactic fermentation (MLF) comes into play. This is the process of converting malic acids into lactic acids and while this happens naturally with almost all red wines, winemakers may have to coax white wines into malolactic fermentation. The timing of the process is key to the successful production of a wine, particularly those of cooler wine producing regions, where acidity levels are naturally high.
In regions such as Northern France, Northern Spain, Germany and Northern Italy, winemakers will utilise this process to ensure their white wine does not become too acidic, whereas in warm climates such as that of California’s Napa Valley, the process is used to ensure wines do not become ‘flat’.
The total acidity of a wine impacts heavily upon its character. A white wine with a total acidity level of one per cent would be considered overly acidic and would have a tart sourness that would render the wine virtually undrinkable. At the other end of the scale, should the total acidity be less than 0.4 per cent, a wine would be flat and lacking in flavour and ‘bite’. The ideal total acidity for a white wine should be around 0.6 to 0.7 per cent.
