After the grapes are harvested, when they arrive at the winery, they are put on conveyor belts, where workers pick out unripe grapes and other undesirable foreign particles. To get the juice out of the grapes, they must first be crushed, and then pressed. Usually a machine called a crusher/destemmer will remove the stems and crush the grapes just enough to puncture the skins. Some juice will run off the grapes (called "free run juice") and be collected. A limited number of wines are made from free run juice only. From there, the grapes will enter a press. The most modern and frequently used press today is a horizontal press, that has an inflatable plastic bladder inside it. The outside of the press has slots in it, so as the bladder gradually expands, the juice runs out of the slots. This pressing process happens slowly, so as to avoid crushing the pips which would release their bitter flavor.