Yuzu: Citrus ichangensis x Citrus reticulata

(yuzu: citrus ichangensis [ichang papeda] + citrus reticulata [mandarin])
october, 2009
carrboro, north carolina

One of the newest leaves on the yuzu tree.

Though it may take years, I'm eager to see if my yuzu will bear fruit. The yuzu is a very obscure citrus fruit in much of the world, though it has a rather rarefied history in Japan and Korea - yuzu have been cultivated in both countries for 2000 years, where sweet and sour variants have been developed, and a wide range of culinary uses are on display.

Many parts of both countries are known for cold winters, and the yuzu is one of few citrus with a reputation for cold tolerance. The fruit looks a bit like a large, yellow tangerine, and has a sour, but very complex flavor akin to a mixture of grapefruit and key lime; an ancient, sweet-tasting cultivar was thought to be extinct before a 1980s re-discovery of a feral grove within a forest in southern Japan. In Japan, yuzu juice is mostly used in savory concoctions; in Korea there are uses for the sweetened juice, including the honey marmalade yuja-cha, which is made from yuzu juice and zest which is combined with pectin and honey. Elsewhere in the world, yuzu is best known as an occasional fragrance, and as a primary ingredient (alongside sudachi juice, soy sauce and saki vinegar) in ponzu sauce.

Yuzu is a wild hybrid, a cross between a mandarin and an ichang papeda. The papedas are a large sub-group of citrus plants which are only rarely cultivated. They all have a number of common characteristics which set them apart from other citrus: winged petioles (giving the leaves an hourglass shape), leaves that are intensely fragrant when rubbed or crushed, and a somewhat more rugged physique than other citrus. Most papeda fruit tend to be either very bitter, or very sour, and are oft-described in botanical literature as "unpleasant tasting." However, they are of some interest, as many of them are more disease-resistant than other citrus, and a few of them are cold-tolerant to a far greater degree than is generally typical of citrus plants. When papedas hybridize with other citrus, the resulting fruit tends to have a very sour, but complex flavor: shangjuan (papeda x pummelo), yuzu (papeda x mandarin), sudachi (papeda x orange?), kaffir lime (papeda x key lime?) are four papeda hybrids that have acquired varying degrees of gourmet interest.

The yuzu is distinctive - rubbing the leaves between one's fingers produces a unique scent: a sweet, spicy, complex, and strong fragrance akin to a mixture of grapefruit and lime, with floral overtones. As the yuzu is especially close to kaffir lime in its' ancestry, I tasted one of the leaves, and though they do have a powerful fragrance, the flavor is a bit less interesting, very reminiscent of lemongrass. The tree itself is rather muscular in structure, even at a height of only 2 feet, with a more rugged and less shrubby stature than other citrus, and a number of rather prominent thorns.

We will see if this tree will bear fruit. The fruit is reportedly the most intensely fragrant of citrus fruits, and in countries where yuzu is cultivated, the fruit is also sometimes kept for its' air-freshening qualities.