Yuzu (fruit and zest)

A citrus eaten for its fragrance

Yuzu, Citrus junos, looks like a bumpy yellow clementine. The fruit is usually 5.5 to 7.5 centimetres across, can reach about 10, and is yellow when fully ripe and green earlier in the season. The skin is uneven and very aromatic, and the tree is an upright shrub or small tree armed with many large thorns and leaf-like petioles. It is a fruit eaten for its smell more than its pulp: the juice is sour and the fruit holds seeds, while the peel carries a potent, distinctive perfume, and it is called a peel-eatable fruit because the peel goes into food as readily as the juice.

In Japanese the fruit is yuzu (柚子) and in Korean yuja (유자). A recipe that asks for lemon or lime in its place gets a sour fruit with a different aroma, because the scent of yuzu is its own. That aroma is carried by the peel oil, which is why zest and juice are separate ingredients, with different uses and different rules for the cook.

In the fermented kitchen yuzu supplies sourness to ponzu and an aromatic top note to seasonings such as yuzu kosho, a paste of citrus peel, chilli and salt.

From the mountains of China to Japan and Korea

Yuzu is believed to have originated in central China, where it grew wild in Tibet and in the provinces of Sichuan, Hubei and Yunnan. It is thought to be a first-generation hybrid of a mandarin, the mangshanyeju type, and the ichang papeda, a hardy wild citrus. A DNA study of Japanese citrus collections supports the papeda link: yuzu clusters close to Citrus ichangensis, in agreement with Swingle’s earlier proposal that it is a chance seedling of that species. The same analysis groups yuzu with ichanchii, hanayu, Kourai Tachibana, rokugatsumikan, lemon and limonia as varieties with more than 80 percent of their markers from the population that represents citron, Citrus medica; the markers of citron and ichanchii lie close together, so the result fits a papeda parent without separating it cleanly from the citron lineage.

From China the fruit went to Korea and Japan, introduced to both during the Tang dynasty, in a period that one account puts at the fourth to eighth centuries. Japan’s citrus is a mosaic of arrivals: the country lies at the eastern edge of the natural range of citrus, has two endemic species, tachibana and shiikuwasha, and received many others, yuzu among them, through prehistoric and historical introductions and natural hybridisation. These have been grown mainly along the coast of south-western Japan. Yuzu has also been grown in California since 1888, although the US Department of Agriculture bans the import of fresh yuzu.

The fruit became part of the calendar. In Japan a bath with yuzu floating in it is traditional at the winter solstice, and in Korea yuja turns up in sugar preserves, tea and a fruit punch. Yuja has been used for food and medicine in China and Korea, and it is mostly prepared as sugar pickles, tea, dressing and vinegar.

Kochi, ponzu and a regional fruit

Kochi Prefecture on Shikoku produces more yuzu than any other part of Japan. The eastern Chugei district gets heavy rain, which suits a tree that needs moisture, and Kochi fruit is known for its size and rich aroma. The harvest falls around November. In traditional Tosa cooking the fruit was paired with foods by season, with autumn yuzu going to moray eel. National production was about 27,000 tonnes in 2016.

Kochi’s modern yuzu story is told through ponzu. Around 1965, as the forestry industry declined, most households already had a yuzu tree in the yard, and people tried to build a business on it. Fresh fruit of good quality was hard to sell from a thinly spread, ageing population with other jobs, so they sold the juice as ponzu instead, and about 1986 yuzu ponzu for home use began to be sold in earnest and became known across Japan. Ponzu in its older sense is yuzu juice mixed with vinegar; ponzu soy sauce adds a kombu and bonito broth, soy sauce and mirin. A rarer ponzu is made from seed-grown trees, which are hard to manage. In 2020 Monobe yuzu from Kami City was registered under Japan’s geographical indication system as a regional ponzu, and ponzu made from other citrus is also sold in Kochi.

Yuzu juice as a vinegar

In the five towns and villages of eastern Kochi’s Chugei area, Nahari, Tano, Yasuda, Kitagawa and Maji, yuzu is a whole food culture, recognised in Japan’s Traditional 100-Year Food list and as part of the Japan Heritage story titled “From a forest railway to Japan’s top yuzu road”. Some of the trees are said to be over 300 years old, and a tradition holds that Nakaoka Shintaro, a samurai activist who served as a village headman in the late Edo period, encouraged farmers to plant yuzu as a sideline.

The local word for the juice is yunosu, and it was used in place of vinegar because it is so acid. It is said to have preserving and appetite-stimulating effects and is sold in large bottles. Yuzu sushi is made with rice seasoned with yunosu, and the local dishes that use the fruit include vinegared dishes, sashimi, nuta with garlic leaves, yuzu miso, yuzu kosho, tsukudani, pickles and yuzu sake. The acid does the job of the vinegar, and the peel and juice add the fragrance.

Peel oil and juice

The two parts of the fruit that reach the kitchen are different materials. The peel is the aromatic one. Cold-pressed yuzu oil, squeezed from the oil sacs in the coloured outer peel, and steam-distilled oil differ in composition. Reconstructions of the two oils, built from their analysis, put limonene at about 53 percent of both, γ-terpinene at 27 percent in the cold-pressed oil and 14.5 percent in the steam-distilled one, and p-cymene at 2.5 percent against 11.5 percent, with myrcene, α-pinene, linalool and β-pinene in smaller amounts and terpinen-4-ol appearing only in the steam-distilled oil. Fresh zest brings the cold-pressed profile to a dish.

The peel is also richer in vitamin C and phenolics than the flesh, and the fruit is called peel-eatable because the rind goes into food as readily as the juice. The peel and seed contain citric acid, and the juice is the acid of ponzu and of the local vinegar substitute yunosu. Green peel holds more of the flavonoids naringin and hesperidin than yellow peel, which is one more reason the colour of the fruit matters when it is bought for a seasoning.

Ponzu at the table, preserves in the jar

Ponzu is served as a dressing or dipping sauce for salads, boiled vegetables, cold tofu, grilled meat or fish, sashimi, potstickers and hot-pot dishes such as shabu shabu. It also works in heated dishes, as a marinade for roasts and as a stir-fry seasoning, and it pairs especially well with grated daikon.

Korea takes the fruit in a sweeter direction. Yuja is prepared as sugar pickles, tea, dressing and vinegar. Yuja-cheong is a marmalade-like preserve of fruit and sugar, yuja tea is made from it, and yuja-hwachae is a fruit punch. Japan has its own yuzu tea and liquors, and the juice and peel go into yuzu miso, tsukudani and pickles in Kochi. The sweet preserves are the older cousins of the sour seasonings: both put the peel to work, one with sugar and the other with salt and chilli.

Zest, salt and time: yuzu in preserved seasonings

Yuzu kosho is the clearest case of yuzu working in a preserved seasoning. In Kyushu, where the name comes from, kosho means chilli pepper, not black or white pepper. The Fukuoka recipe published by the Ministry of Agriculture, Forestry and Fisheries uses green chilli and the peel of green yuzu with salt. It calls for the peel to be pared with a knife, chopped and blended with the chilli and salt. The fruit used is the green yuzu of around September, because the fruit turns yellow as it ripens in autumn and winter, and green chilli is in season from July to September, so the two overlap. Batches are often frozen in portions for the rest of the year.

Salt sets the balance. The recipe notes that more salt extends shelf life and keeps the green colour stable but dulls the yuzu aroma, while less salt lets the chilli fade faster; stored refrigerated, the paste keeps its green colour until the next season. Red chilli is sometimes used instead and is more aromatic. Recipes vary by region and household, and several places claim the origin, one candidate being the Hikosan area of Fukuoka, where mountain ascetics reportedly used local yuzu as medicine.

The acid in yuzu juice does not cure or preserve a seasoning on its own. In ponzu, citrus juice, soy sauce and vinegar are the basic ingredients: the citrus and vinegar give sourness, the soy sauce saltiness, and soy sauce and dashi ingredients such as kombu, bonito and shiitake add umami. Yuzu is the best known citrus for it, but sudachi, kabosu, shikuwasa and lemon are also used, alone or in blends such as yuzu with lemon. Strictly, a lighter citrus seasoning is ponzu and the soy-blended version ponzu soy sauce, although everyday speech calls both ponzu. It is the soy sauce and mirin in ponzu soy sauce that have fermentation histories of their own. Because it contains fruit juice, commercial ponzu spoils more easily than other sauces, and the advice is to refrigerate it after opening and use it within two to four months, following the label.

The tree and the season

Yuzu is relatively frost-hardy and can be grown where winter temperatures fall to about minus 7 degrees Celsius. The plant is an upright shrub or small tree with many large thorns. The Kochi producers say their fruit is grown without pesticides, a producer claim and not a standard.

The season has two halves. Green fruit comes first, with the best yuzu for kosho picked from around September, and the fruit turns yellow as it ripens through autumn and winter, with the main harvest in Kochi around November. A cook who wants the green aroma and colour for kosho buys early; one who wants yellow fruit buys later.

Choosing and handling

Fruit sold in autumn can be green or yellow, and the colour tells which job it suits: green for kosho and for sharp aroma, yellow for juice and for the bath. The Fukuoka recipe asks for the peel to be carefully pared with a knife before it is chopped. Batches of kosho are often frozen in portions so they can be used through the year.

How yuzu is used

In Japan the zest and juice go into ponzu, yuzu kosho, yuzu tea and liquors. Ponzu is served with hot pots, vinegared dishes, grilled fish, sashimi, chilled tofu and salad dressings, and a simple dressing mixes three tablespoons of yuzu ponzu with a tablespoon of ground sesame, a teaspoon of sugar, half a teaspoon of soy sauce and a tablespoon of sesame oil. Yuzu kosho goes with hot pot, udon and somen noodles and sashimi, and sits in many dishes as an accent. Because the juice is so sour and the zest so fragrant, a little goes a long way, and recipes use yuzu as a seasoning, in drops and gratings, far more than as a fruit to be eaten whole. In Korea the common uses are yuja-cheong, a marmalade-like preserve, yuja tea and the fruit punch yuja-hwachae. The wood of the tree is used for the body of the taepyeongso, a Korean oboe.

Notes

Recipes for yuzu kosho vary with the region and the household, and the salt level is a matter of taste and keeping quality.