mash
Crush cooked food to a coarse or smooth paste with a fork, masher, or ricer. A splash of the hot cooking liquid loosens it, and a few lumps are usually fine. Mashing some of a stew's cooked potato and stirring it back in is a classic way to give it body without flour. Don't use a blender or food processor on potatoes -- over-worked potato starch turns gluey.
How to do it
Cook the food until it's completely tender -- a fork or knife should go in with no resistance -- and drain anything watery thoroughly. For potatoes specifically, let the excess steam escape after draining so the mash doesn't turn watery, then mash while it's still warm. Add butter, cream, milk, cooking liquid, or another liquid gradually rather than all at once, since it's much easier to loosen a mash further than to take liquid back out of one. In a soup or stew, mashing only part of the cooked potato or beans and stirring it back in is a reliable way to add body without needing flour.
Common pitfalls
- Undercooked food -- it leaves stubborn, hard lumps behind.
- Over-processing potatoes -- the texture turns sticky and glue-like.
- Adding too much liquid right away -- it's easy to loosen a mash further, much harder to fix one that's already too wet.
- Using cold dairy in large amounts -- it cools the whole mash down fast.
Why it works
Cooking softens cell walls, and in starchy food it lets starch granules absorb water and gelatinize. With potatoes, the goal is separating the individual cooked cells while releasing only a controlled amount of starch -- an aggressive blade in a food processor or blender ruptures far more cells than necessary and releases a large amount of gelatinized starch, which forms a sticky network and produces the gluey texture of an overworked mash. Other food, like beans or squash, is much more forgiving and can often be blended on purpose without the same risk.
Equipment
Different tools give different textures: a fork for a rustic, chunky mash; a potato masher for something moderately smooth with a little texture left; a ricer for very fine, fluffy potatoes with minimal working; a food mill for smooth results at larger volumes; a blender or food processor for many vegetables and legumes, though generally not for standard mashed potatoes. A ricer is one of the most reliable tools for getting consistently smooth potatoes.