Ducks swim in the water at a breeding base in Gaoyou, China.
CNN  — 

“Would you like salted duck egg with that?” asked the cook.

I was on a trip to Yangzhou in China’s Jiangsu province and had popped into a small eatery for a bite of breakfast, ordering congee and a side of pickled vegetables.

Before I could respond, the cook disappeared into the kitchen, then reemerged holding a grayish-green egg balanced on a plate.

“Sure,” I nodded.

Plain congee, after all, pairs best with sour or pungent condiments that pack a lot of punch. And in my experience, the sharp flavor of salted duck eggs – cured in brine to produce salty whites and rich, creamy yolks – could be even more stimulating than a cup of joe.

When the meal arrived, I sliced the egg open, ready to spoon out the fatty yolk.

But as the two halves of the egg teetered on the plate, I instinctively did a double take. Not one, but two oozy, bright-orange yolks rested in their egg-white cradles.

Amazed, I waved the cook over to show him this rarity.

He chuckled, then explained that most of the salted duck eggs in their kitchen contained two yolks. They’d been brought over from a county situated within Yangzhou, called Gaoyou. There, something most places would consider a rare and random anomaly is in abundant supply.

Salted duck eggs: A gastronomic specialty

The phenomenon of double yolks occurs in up to 10% of the eggs laid by Gaoyou ducks.

“When we talk about double-yolk eggs, we think of Gaoyou,” says David Yan, a Jiangsu native and WildChina travel guide. “This county is especially renowned for these eggs, and has got a reputation.”

It turns out that Gaoyou’s geographic position makes it ripe for the production of salted duck eggs.

The county is situated in a region with plentiful waterways, such as Gaoyou Lake (the province’s third largest freshwater lake), which for centuries has enabled the local waterfowl industry to thrive.

But that’s not the only way in which the natural environment practically predestined Gaoyou’s eventual claim to fame. Salt, which is necessary for curing the duck eggs, is bountiful in the area.

Northern Jiangsu province’s salt marshes, which are now part of a biosphere reserve where visitors can go birdwatching and hiking, were once primarily known for being a major source of China’s salt.

“That was the epicenter of the salt industry,” explains Miranda Brown, a professor of Chinese studies at the University of Michigan. “You have the lake for the duck, and then you have the salt industry literally next door.”

A worker at Jiangsu Gaoyou Duck Co. Ltd uses a light to search for double-yolk eggs.

In the city of Yancheng (literally meaning “Salt City”) not far from Gaoyou, a vast network of crisscrossing waterways connects the coastal salt marshes to the Grand Canal, a huge manmade river that allowed salt producers to make a handsome profit selling to the rest of the country.

“Salt merchants were rich and had very fine tastes,” says Brown. “They threw lavish banquets that would last all day and pull together the most exquisite foods.”

What wealthy people ate was often considered a benchmark for what constituted fine dining, and writers and poets who rubbed shoulders with the affluent merchants would pen treatises about the food.

In the late 18th century, the Qing-Dynasty scholar and gastronome Yuan Mei wrote in “Recipes from the Garden of Contentment” (translated in 2017 by Sean J.S. Chen): “Salted eggs from Gaoyou are very good, with deep reddish yolks loaded with oil.”

Such references helped cement salted duck eggs as a gastronomic specialty of Gaoyou, entwined with the area’s very identity.

That association continues to run deep today; according to the Chinese search engine Baidu, choirs in Gaoyou regularly perform a folk song called “数鸭蛋” (Shǔ Yā Dàn, which literally translates as “Counting Duck Eggs”) that celebrates the local specialty.

This sort of culinary regionalism was and still is common throughout China, with different areas becoming associated with particular food products.

According to Brown, the tendency for these correlations stems largely from the country’s vast size and diverse topography, which “leads to different culinary possibilities. That becomes a way that people start to identify places and regions and even people – by the foods that are best grown in those areas.”

For example, pu-erh tea from the mountains of southwest China’s Yunnan province is revered across China, while Inner Mongolia Autonomous Region’s vast pastures, ideal for sheep herding, produce much of the country’s mutton.

Gaoyou's waterways are a popular tourist attraction.

In similar fashion, Gaoyou became recognized for environmental conditions that favored salted duck eggs.