The term “haricot beans” can refer to a number of small, white dried beans in the Phaseolus genus, all of which cook easily and can be substituted for one another in recipes. The best haricot beans have a consistent color, texture, and size. They lack wrinkles or discoloration, have an oval or kidney shape, and are white to cream in color, rather than light brown. Fresh haricots may be sold in their shells, which are brown and relatively dry at harvest time, but should never be moldy.
Haricot beans come in three main types: large, kidney-shaped beans also called cannellini or fagioli beans; medium-sized oval specimens known as great northern beans; and small, pea-sized roundish beans called navy beans, Boston beans, or pearl haricots. All these beans are quick cooking and take only about an hour to soften. They also all have light-colored and tender skins, tend to keep their shape after cooking, and produce a mild, nutty-tasting dish. Haricots tend to take on the flavors of other foods with which they are cooked. You can substitute any one of these three types for another in soups, baked beans, or salads, as well as traditional European dishes like pasta e fagioli or ragouts.
When choosing dried haricot beans, look for specimens that all have the same general size and shape, as very large beans will cook more slowly than small ones in the same pot, potentially producing a crunchy dish. Avoid broken or deformed beans, which are also unlikely to cook well. Good haricot beans should have unwrinkled off-white to cream-colored skin without any dark or chalky spots, a consistent size and shape, and should contain few to no rocks or pieces of dirt. Darker or wrinkled beans may be old and can take a very long time to cook, even if presoaked before boiling.
You may encounter fresh haricot beans in the farmer's market or in specialty grocery stores. They may be sold loose or still in their pods, which should be papery and tan to light brown. Avoid beans in pods with dark mildew speckles on them or on which fuzzy mold is growing, since the mold on the outside can affect the quality of the seeds inside. The beans themselves should look a lot like their dried cousins, but will be larger and with more translucent skins. Fresh beans cook more quickly than the dried variety, but can be used in the same kinds of recipes.