The five basics tastes are umami, sweet, sour, bitter and salty. Sour flavors are found naturally in fermented foods like pickles and fruits like lemon, grapefruit, orange, grape and melon. To make food taste sour, simply add natural extract or juice from fruit. You can also achieve a sour flavor during the cooking, baking or food preparation process via man-made sour flavorings like artificial lactic acid or fumaric acid. Both methods introduce sour acid into the food, however artificial flavorings must be listed in the ingredients -- an important consideration for commercial food service applications.
Slice the fruit into palm-sized pieces using a knife. If you choose to use artificial flavoring, skip to step three.
Insert the fruit pieces it into a juicer or food press to coax the juices away from the fibrous components of the fruit and into a separate glass or container, usually provided with the juicer or press.
Pour the extract -- natural or artificial -- onto the food you wish to make sour. This works equally well for garnishing cooked food or mixing into food bases like cakes, dips or drinks.