Natto, sometimes described as a kind of “vegetable cheese ,” is a traditional Japanese dish made with cultured soy beans . And on July 10, Japan celebrated a day devoted to the food , with many Twitter users uploading photos using the hashtag #NattoDay  (#納豆の日).
＼(・ ω・)／ﾅｯﾄｩ pic.twitter.com/wcBBhZcbHq 
— IBK44 (@IBK44) July 9, 2017 
Image caption: July 10 is Natto Day!
Tweet: It's Natto Day!
＼(・ ω・)／ “Natto!”
Natto is a popular yet polarizing part of Japan's culinary culture. Many people love natto for its “umami ” flavor and health benefits, while others are put off by the fermented food's strong odor and stickiness .
The food is commonly sold in styrofoam packets, and is mixed with hot mustard and a rice vinegar-based sauce. Many Japanese have their own locally produced brands of natto, such as this packet of natto, sold in the city of Morioka, in the northeastern prefecture of Iwate:
7月10日は『納豆の日』だな。盛岡市は都道府県庁所在地ランキングで、納豆の消費金額・消費量ともに毎年上位さなるぐれぇ納豆好きの人が多いんだなっす。 pic.twitter.com/SYIJWD4Sbe 
— わらしちゃん (@warashichan_pnk) July 10, 2017 
So, July 10 is Natto Day. Apparently when compared to other cities across Japan, in terms of money spent and sheer sales volume every year the city of Morioka climbs of the rankings. We certainly love natto here.
The fermented beans are quickly mixed with chopsticks before eating. A key feature of natto are sticky strands that are sometimes difficult to deal with:
— べんぴねこ (@benpineko) July 10, 2017 
#PanPakaPantsu  (a cute anime with an underwear theme)
Natto can be eaten in a variety of ways, with a variety of toppings. A fishing cooperative in Kasumigaura, a seaside town in Ibaraki, just north of Tokyo, has some suggestions about what to eat with natto on Natto Day.
明日7月10日は #納豆の日  霞ヶ浦北浦の湖の幸からつくられる佃煮や煮干しは納豆との相性バツグンです。納豆パワーに小魚カルシウムを加えて暑さに負けない元気を(^_^)/ #シラウオ佃煮  #シラウオ煮干し  #アミ佃煮  #アミ煮干し  #霞ヶ浦  #北浦  #茨城県  pic.twitter.com/32T3HLl1KU 
— 霞ケ浦北浦水産事務所 (@kasumigaura000) July 9, 2017 
July 10 is #NattoDay. This dried and stewed baitfish goes extraordinarily well with natto. Combining the power of natto with the calcium of fish and beat the summer heat, and keep going in the months ahead. (^_^)/
As for why July 10 has been declared Natto Day, Hana Kotoba, a website devoted to the symbolism of Japanese words, explains:
「必ず来る幸せ」 pic.twitter.com/h9j4op9KuH 
— はな言葉 (@hanacotoba_jp) July 9, 2017 
Today, July 10, is Natto Day:
It come from the combination of 7 (sometimes pronounced as ‘nanatsu’, or ‘na’), for July, the seventh month, and 10 (sometimes pronounced as “toh”).
The saying associated with ‘daizu’ (大豆, the beans used to make natto) is “luck will always come.”
This article has been updated to reflect that natto is made from cultured soy beans, and is not fermented.