[4][1][5] It is prepared by boiling the bones in water for up to eighteen hours, at which point the soup becomes cloudy in appearance.

[4] The dish is traditionally topped with chāshū (sliced pork belly), and additional ingredients can include kombu, kikurage, shōyu, chili bean paste, and sesame seeds.

[2] Some ramen shops allow customers to select the level of firmness, including futsu for regular or standard, harigane for very hard, barikata for al dente, and yawamen for soft.

[2] Some restaurants also provide a second order of noodles if requested by the customer, in a system referred to as kaedama.

[2] Tonkotsu ramen was invented in 1937 by Tokio Miyamoto, a yatai food vendor, in Kurume, Fukuoka Prefecture, in northern Kyushu.