The situation is quite different when grapes are grown in warm regions like the interior valleys of California. Here, the acid content of ripe grapes often falls between 0.4 and 0.8 percent. Grapes grown in such warm climates often have too little acidity, and wine produced from grapes low in acidity is often bland and flat tasting. Besides producing bland wines, fermenting grapes low in acidity often results in other problems, and adding acid to grapes grown in warm regions is a standard winemaking practice. Large acid additions are best made before fermentation is started.
French winemakers use a different convention.
They express titratable acid as if all the acids present were sulfuric acid. These different customs result in different numbers, and sometimes novice winemakers are confused by the different conventions. Grape acids differ considerably in strength. Tartaric acid is stronger than malic acid, and malic acid is stronger than citric acid. High acid grapes have a low pH, and low acid grapes have a high pH because of the upside down scale.