To press means to exert pressure on grapes to extract their juices. A press is a device used to do that. There are many kinds; one of the simplest and oldest is the hand-operated wooden basket press. A more modern press—the bladder press—is essentially a horizontal tank with an inflatable membrane running through its middle. As the membrane swells, it gently squeezes the grapes against the side of the revolving tank. Grape bunches can be put whole into a press, but more often, they are crushed and the stems are removed first.