Beijing Bianyifang Roast Duck Restaurant specializes in shuxiangya (vegetarian aroma duck). Provided to China Daily

What makes one Peking duck stand out from the next? It's all in the roasting, as Ye Jun finds out from the oldest restaurant still serving this capital city signature dish.

It is not easy preserving an age-old culinary tradition while balancing the need to cater to modern taste buds. This is especially so when the method you are talking about has been around for nearly 600 years.

Beijing Bianyifang Roast Duck Restaurant was founded in 1416, more than 400 years before Quanjude, arguably the city's most recognized name for roast duck. Quanjude was established in 1864.

Bianyifang is known for guarding its traditional closed-oven roasting technique, which Quanjude had abandoned in favor for open-oven roasting - to cook the ducks faster and to make it easier for the chefs. Since the 1970s, Quanjude had expanded as an epicurean phenomenon, and the open-oven technique became more prevalent in Beijing.

Bianyifang was relegated to the sidelines.

So, when Beijing chef Sun Lixin joined Beijing Bianyifang Roast Duck Group 10 years ago, he found some major problems with its closed-oven roast duck.

"The duck tasted greasy. When it turned cold, there was an unpleasant smell," he says. "Its nutritional value wasn't so balanced, because there weren't many vegetables in the dish. The green onion served with the duck left a bad taste in the mouth."

Sun, deputy general manager and executive chef of Bianyifang, says there were other reasons why Bianyifang was left by the wayside as Quanjude enjoyed its glory days.

"In the 1970s, Peking roast duck became part of China's foreign diplomacy, along with table-tennis," Sun says.

"At the time, Qianmen Quanjude was a big restaurant on the main street, while Bianyifang was a small eatery inside a hutong. So the government chose Quanjude as the place to host foreign guests, giving it a lot of publicity and support."

Quanjude is managed by the Beijing municipal government, while Bianyifang is managed by the Dongcheng district government - which may also have influenced their respective development.

But, over the years, Sun and his colleagues worked hard to overcome the disadvantages, giving the closed-oven roast duck a makeover and a healthy image.

In 2005, Sun invented shuxiangya (vegetable aroma duck), which later received a patent. "Before we roast the duck, we soak it in vegetable juices for five to six hours, and we pair the roasted duck with vegetables when we serve it," he says.

Preparing a Peking roast duck takes at least four steps: preparing the duck, pumping air beneath the skin, drying and roasting.

Sun added a step before roasting - soaking the 3-kg duck in pure juice extracted from 10 types of vegetables.

The vegetable juice, being alkaline, eliminates the pungency of the duck but also reduces the duck fat beneath the skin.

At the same time, the skin retains the fragrance and tempting luster of traditional roast duck.

Sun has kept to traditional closed-oven roasting where the brick oven is preheated for five hours before 10-20 ducks are put inside and roasted for 45 minutes at about 200 C.

There is no direct contact between the fire and the duck, which reduces the risks of carcinogens from carbon, Sun says.

The ducks are also sliced differently. At Bianyifang, they are slivered in the shape of an "elephant eye", with the skin and meat together so diners can enjoy both the tender meat and fragrant, crisp skin.

Bianyifang's duck is served with two kinds of pancakes - red and green. The red one is colored with carrot juice while the green has celery juice added. Side dishes include turnip sprouts, toon sprouts, lettuce and mint leaves, without the traditional shredded green onions.

Sun says that when he joined Bianyifang, the restaurant group was at its lowest point. "Traditional dishes were not passed down nor protected sufficiently. Dishes became out of date. The service and environment fell behind the times.

Traditional dishes no longer tasted good," Sun says.