The grapefruit is a sweet/sour citrus with orange skin and red, acidic flesh. It was accidentally created by combining sweet orange and pomelo. The fruit clusters together on the tree (like grapes). Other varieties can have pink, orange, yellow, or white flesh.
A good grapefruit feels heavy for its size and has thin, smooth, firm skin. No discoloration. They last a week at room temperature and three weeks in the refrigerator.
Grapefruit is a popular diet breakfast. Cut one in half horizontally, pour some sugar on it, and dig in with a spoon. You can also sprinkle them with brown sugar and cinnamon, then broil for a fancy, healthy dessert.