What do foods that taste sour usually contain?

* Citric Acid: Found in citrus fruits like lemons, limes, oranges, and grapefruits. It's also added to many processed foods and drinks for a tangy flavor.

* Malic Acid: Found in apples, pears, and grapes. It contributes to the tartness of these fruits.

* Tartaric Acid: Found in grapes, especially those used for winemaking. It adds a distinct, crisp sourness.

* Acetic Acid: This is the main acid in vinegar, which is made by fermenting alcohol. Vinegar is used to add sourness to dressings, marinades, and sauces.

* Lactic Acid: Produced by the fermentation of milk sugars. It's found in yogurt, sour cream, and cheese.

* Phosphoric Acid: Found in some soft drinks, giving them a tart flavor.

Note: While these acids are the primary contributors to sourness, other factors like the presence of sugars, salt, and other flavor compounds can influence the overall taste perception.