Get the most out of your mangosteen! The skin of mangosteen oozes a bitter sap. When mangosteen is underripe this sap is likely to get onto the fruit when you cut it open and the fruit inside will be hard. To make sure you get the most out of your mangosteen, wait until it is dark purple (almost black) to eat. Cut open the hard shell with a knife and pull the shell apart. Eat the soft white meat on the inside. Do not eat any of the skin and avoid getting the sap from the skin on the fruit as this will add bitterness to the flavor. Enoy your mangosteen!