Doyo no Ushi no Hi (The Ox Day During Doyo) (土用の丑の日)
Doyo no ushi no hi' is the Ox day (based on the twelve signs of the Chinese zodiac) during the "doyo" (the period of about 18 days at each end of four seasons).
It is customary for Japanese to eat an eel on the Ox day during doyo of summer, in order to take nourishment and overcome the heat.
Occasionally, the Ox day comes around twice during each doyo, and the second Ox day is called 'ni no ushi.'
Generally speaking, the Ox day during the doyo indicates the summer one, but as the doyo comes around four times in a year, the day also comes around several times in a year.
Recently, a campaign to eat eel on doyo in winter has been run in mainly Okaya City, Nagano Prefecture, which ranks high in per-capita eel consumption.
The Ox day during the summer doyo, 2004 to 2011
- July 21, August 2
- July 28
- July 23, August 4
- July 30
- July 24, August 5
- July 19, July 31
- July 26
- July 21, August 2
Ni no Ushi
As mentioned above, the day often comes around twice. With 'Heiki-ho' (the method of placing the 24 traditional seasonal divisions of a year by making equal time intervals), the doyo days of summer are calculated as the 18 days before 'risshu' (the first day of autumn), and with the recently popular 'Teiki-ho' (the method of placing the 24 traditional seasonal divisions of a year by equally dividing the ecliptic into 24 parts, calculating the date when the sun passes each of those parts and setting the seasonal divisions into the date), the doyo days of summer fall on the dates the sun passes the obliquity of 117°to 135°, and they are calculated as approximately 18 days around risshu. Provided that the doyo has 18 days, the Ox day comes around twice when the first Ox day comes within 6 days from the first day of the doyo, in other words, when the first day of the doyo falls on the day of the Monkey, Cock, Dog, Boar, Rat or Ox (based on the twelve signs of the Chinese zodiac). This second Ox day is ni no ushi, and it comes around almost every other year.
Origin of the custom of eating eel on the Ox day during the summer doyo
There are various theories regarding the origin of the custom of eating eel on the Ox day during the summer doyo, but the best known of them is that the idea was devised by Gennai HIRAGA, who came from Sanuki Province. This story is included in "Meiwa-shi" (a book about food customs in the time around the Meiwa era), which was written by Hakuho AOYAMA in 1822.
It states as follows:
The owner of an eel restaurant, having few customers, went to Gennai's home to consult about how to sell eel during summer, the sluggish season for his business. Getting a hint from the folklore that "one could overcome the summer heat by eating something that had the Japanese syllable of 'u' at the head of its name, such as an eel (in Japanese, 'unagi') on the Ox day," Gennai recommended that the owner attach a poster to the shop door stating, "Today is the Ox day." So the owner followed Gennai's advice, and greatly prospered, because people came to eat trusting Gennai, who was well known for being knowledgeable. And so, other eel restaurants followed suit, and the custom took root.
If the folklore is the rationale for the custom, the food to eat on the Ox day during the doyo could be 'udon' (Japanese wheat noodle) or 'udo' (Aralia cordata), since every food other than eel is possible when it has the Japanese syllable "u" at the head of its name.
The custom became popular, but it has no certain history or origin and could be called the product of what we now call commercialism; like chocolate on St. Valentine's Day, or 'eho-maki' (rolled sushi that is said to bring luck when eaten in 'eho' [the lucky direction]) on 'Setsubun' (February 3).
Eel, however, is rich in Vitamin B, so one can prevent summer fatigue and loss of appetite by eating it. Considering this, the old custom of eating eel in summer can be said to make sense.
The Zenbei HARUKIYA origin theory: According to "Edo kaimono hitori annai" (the shopping guide of Edo) compiled in the same Bunsei era (1818-1829) as the above, Zenbei HARUKIYA, an eel restaurant owner received a large order for 'kabayaki' (eel split, grilled and basted with a sweet sauce) during the doyo, so he grilled eel on the day of the Rat, Ox and Tiger consecutively and kept it in earthenware pots;
of these eels, only the ones grilled on the Ox day retained their good flavor, so this gave rise to the custom, the guide states.
The Shokusanjin origin theory: According to "Tenpo kawa (Good Stories in the Tenpo era)," compiled by Daihenho RYUKAISAN a bit later in 1839, Nanbo OTA (also known as Shokusanjin) was consulted also by an eel restaurant owner, Nanbo devised a tag line in the style of kyoka (a comic tanka [Japanese poem]) saying that "eating eel on the Ox day was good for one's health."
An ox = two eels theory: The Japanese syllabary characters meaning an ox ("うし"), which were written on something with a brush and India ink, looked like two eels, so they became the origin of the custom, this theory states.
There has been an advertising campaign to promote the consumption of eel on the Ox days other than the summer one, which has been carried out mainly by eel mariculturists. Similar campaigns have been carried out by supermarkets and convenience stores. Doyo is at the change of seasons, so to some extent it's reasonable to eat eel, which has high nutritional value and benefits one's strength.
In 2007, eel sales fell sharply in Japan because consumers were concerned about the safety of eel imported from China.
Please refer to the article on 'the safety of Chinese foods'