The quince is the hard, knobbly, intensely fragrant golden pome of Cydonia oblonga, the lone species of its genus and a close cousin of the apple and pear in the rose family. Almost inedible raw — astringent, sour and rock-hard — it is a fruit made by cooking, which turns its pale flesh rosy and sweetly perfumed and sets it, thanks to abundant pectin, into the firm ruby paste known as membrillo or quince cheese.