A black egg, also known as a century-old egg, is a Chinese food item made by preserving duck, chicken or quail eggs with ash, clay, salt, quicklime and rice hulls for up to a few months.

As a result, the egg's yolk turns dark green or gray with a creamy texture, while the egg white become semi-transparent and jelly-like.

Crab soup is a common starter dish found in many Vietnamese restaurants, made with shredded crab, bone broth and shitake mushrooms, as well as tapioca starch which thickens the soup.

Pair it with black eggs and you get a popular afternoon street snack loved by many in HCM City for its affordability.

Crab soup with black eggs is a popular street food in HCM City for its taste and affordability. — VNS Photo Việt Dũng

For three years, Nguyễn Thị Bích Phượng has been running a small restaurant specialising in crab soup with black eggs, named Súp Cua Pích, in District 3. She typically adds pig brain to her soup, which makes it creamier.

"I helped out at my sister's restaurant in District 4 for more than 10 years. She taught me the necessary skills, so I opened a restaurant myself. I enjoy cooking and feel that our soup is of high quality, so I wanted to open up my place, too," Phượng told Việt Nam News.

The rich, flavourful and slightly salty black eggs pair very well with the thick, savoury soup, with a light hint of sweetness from the crab. An optional spoonful of chili paste can stimulate the tongue and enhance the flavour even more.

" An important factor is how we stew the pork for the right amount of time so that the soup can smell and taste great," Phượng said.

Some customers find black duck eggs to be too fatty, so she found a supplier of black quail eggs, which many customers have liked.

Her restaurant sells mostly to office workers and students in the afternoon, said Phượng as she prepared soup for waiting food delivery workers.  

Office workers sometimes eat crab soup with black eggs in the afternoon as a quick boost of energy. — VNS Photo Việt Dũng

​Another popular place for eating the soup is at a small street vendor on an alley near the Notre Dame Cathedral in District 1.

"For nearly 30 years I have been helping out at this stall run by my friend. Our stall is popular since our price is cheap despite being in District 1, and customers like our seasonings," Trần Thị Hồng Mai said.

Huỳnh Văn Lộc, a customer, said that office workers who want a light lunch tend to be hungry in the afternoon, so the dish is a great boost of energy.

A visitor to Mai's stall, Helen Nguyễn, who was on her way to catch a flight back to Hà Nội, said she wanted to make time for a quick bowl of crab soup with black eggs.

"There are no dishes like this in Hà Nội where I'm from. This soup is a Saigon specialty and because it is affordable, everyone can enjoy it. Every time I visit Saigon for work, I always eat this soup."

While not everyone may enjoy black eggs, she noted that the egg is the unique characteristic of the soup. "If you visit Saigon, you have to try crab soup with black eggs!" — VNS