In breadmaking, the yeast is set working by the addition of sugar and warm liquid, and is mixed and kneaded with flour and left to prove, or rise. The dough then has to be knocked back or lightly rekneaded, and shaped to fit the tins when these are used. Dough should be kneaded on a floured board, which means folding it over on itself and pushing with a firm rocking motion until the dough becomes smooth and shiny. A dough hook on an electric mixer is an inexpensive attachment which speeds up the work, and ensures that the yeast is worked right through the dough. If bread is to be baked as rolls or freehand shapes, a slightly firmer dough is needed than for bread baked in tins.