Natural acids impart tartness or sourness in food and wine but can be important to balance other tastes.

For example, some sweeter wines like White Zinfandel and many Rieslings also have a very high acidity. You don't necessarily taste the acid, but if it wasn't there the wines would taste too sweet or cloying.

White wines are generally higher in acidity than red wines, and dry wines tend to taste more acidic because they do not have the sweetness balancing and disguising the sour taste.

If a food is strongly acidic, or sour, it will also upset this balance in a wine and make it taste very sweet in comparison. This can sometimes be a good thing, however. An acidic dish can mellow out a highly acidic wine and make it taste fruitier, for example.