Minecraft wiki entry for Cocoa_bean_farming, associated text: Piston harvested farms use a single line of jungle logs, planted on all 4 sides with cocoa plants. Pistons either push the trunk, causing the grown beans to be removed, or scrape the beans from the trunk. (Other designs raise and lower the trunk in rapid succession; but these utilize more complex redstone circuits and are not significantly more useful, cheap or efficient than simpler designs.) Piston designs suffer from universally low yields, somewhat expensive and complex circuit design (compared to alternatives) and general space inefficiency.