Yuzu is a variety of citrus fruit that is cultivated in Asia. The trees produce distinctive sour fruits which are used in Chinese, Korean, and Japanese cuisine; Western cooks have recently adapted the flavor of the fruit for their own purposes. In some regions, the plant is also grown ornamentally, in which case it may produce inferior fruit. Cooking ingredients such as whole yuzu, rind, and juice are sometimes available in Asian markets; for people in the right climates, this tree can also be grown at home.
One of the more remarkable traits of the yuzu tree is that it is very frost hardy. It can withstand cooler temperatures than many other citrus fruits, thriving in USDA zones nine to 11 and sometimes even further north, under the right conditions. The trees also tend to be relatively small, but they produce a high volume of the aromatic fruit when they are well cared for.
This citrus cultivar is more formally known as Citrus junos. It is believed to be a cross between sour mandarins and the ichang papeda, a type of lemon. The fruits appear to have arisen in China, where they were cultivated for some time before being introduced to Japan and Korea. In all of these nations, it is possible to find wild trees, as well as yuzu plantations, and the Japanese have developed a specifically ornamental cultivar that produces beautiful and aromatic flowers.
There are a number of uses for yuzu in Asian cuisine. The sour juice is often used in sauces, such as the Japanese dipping sauce ponzu. The juice is also used in cakes and desserts, along with the rind, which may sometimes be candied. The Koreans sometimes make a version of marmalade with yuzu, and a variety of other jams, jellies, preserves, and spreads are made from the tart, extremely aromatic fruit. The fruit is also treated to extract its essential oil, which is mixed in with bath products and scented candles.
The color of a yuzu can vary from yellow to green when ripe, and the fruits typically are around tangerine sized, with very irregular, knobbly surfaces. A special variety known as lion yuzu has especially knobbly skin. If you are in a region where fresh fruit is available, look for specimens without soft spots, but do not be too concerned about discoloration and uneven skin, as these traits are normal. In an area where it is not available fresh, you may be able to purchase juice or powdered forms; if nothing is available, go for a sour grapefruit, which is probably the closest common flavor approximation.