Almost any little spud can and will call itself a "new potato" these days. But they're just pretending. A truly new potato is something special, and one of the great treats of spring.
To understand new potatoes, you need to know something about old potatoes. About 99% of all the potatoes you'll ever eat have been grown to maturity, dug from the ground and then "cured" – stored for a period of 10 days to 2 weeks in a climate-controlled environment. This toughens up the peel and reduces the amount of moisture in the potato to help it last longer without spoiling.
Truly new potatoes are sold right after harvest, without any curing. They're higher in moisture so have a little bit different texture, and their flavor has, to my taste, a slight bitterness that complements the earthy flavor.
Oddly enough, though "new potato" is usually used to describe small potatoes, truly new potatoes can be any size, ranging from marbles to bakers.
Because these true new potatoes are such a special ingredient, treat them simply, at least the first time you serve them. One of my favorite things is just to steam them until tender, then toss them into softened butter you've whipped with fresh herbs and shallots. Stir just until the potatoes are evenly coated, sprinkle with coarse salt and serve.
How to choose: The best way to tell truly new potatoes is to rub the skin with your thumb -- it should be delicate enough to scrape clean.
How to store: New potatoes can be stored at room temperature, but because they have not been cured, they won't last as long as regular potatoes -- several days instead of several weeks. When refrigerated, the starch will begin to convert to sugar, so if they're chilled for very long they'll taste sweet.