The popularity of sour noodles lies in their simple preparation method and the auspicious aspirations behind their origin. It was said that Liuxiu（刘秀） (Emperor Guangwu of the Eastern Han Dynasty) was being chased by a rebellious army. When he was down and out in Luoyang, a kindhearted peasant gave him a bowl of noodles mixed with sour soymilk and vegetables. Suffering from severe hunger, Liuxiu found the noodles incredibly delicious. When he was returned to his throne, the emperor added this lower-class dish to his imperial menu.
The three elements that make Luoyang gravy soup unique are time, seasoning and water. Time is usually the most important element with regard to the quality of the gravy. The more time spent making it, the better the gravy will taste.
Gravy soup is the most common breakfast food of locals. The best companion for the gravy is dry bread. There is even an old saying expressing the love for gravy in the morning: "Hot gravy in the morning, wouldn't change it for being an immortal."