Preparing stock with a generous portion of chicken bones, creating an Indian curry with the Chinese delicacy of fish head and braising duck instead of goose for a Teochew dish.

These are some of the things that make Singaporean cuisine unique, said the owners of Spring Court, Huat Kee and Muthu's Curry, some of the country's oldest family-run restaurants.

Singapore food typically features stronger flavours, they added.

The stories of such restaurants feature in an upcoming book called Delicious Heirlooms, a Straits Times Press publication that will be available from mid-February.

The book's writer, Ms Ow Kim Kit, a 43-year-old lawyer, highlights the owners' perseverance to keep their businesses within the family despite potential buyout offers.

A total of 10 restaurants are featured in the project supported by the National Heritage Board (NHB). The criteria Ms Ow set was that the family food businesses must be at least 50 years old by next year.

The other restaurants profiled are: Fatty Weng, Guan Hoe Soon, Islamic Restaurant, Ka-Soh (Swee Kee), Ming Chung Restaurant, Sabar Menanti and Samy's Curry.

The book not only chronicles their back stories, but also includes input from younger members of the family-run businesses on how they plan to keep the restaurants and the spirit of their forefathers alive.

Ms Ow, who spent two years interviewing and writing while juggling the demands of her day job, said that the book aims to "serve as a record of Singaporean food heritage".

NHB has co-funded a total of 11 food-heritage-related projects since 2013. Delicious Heirlooms is its 12th.

Its assistant chief executive of policy and community Alvin Tan said: "We supported the publication because it presents a slice of Singapore's food heritage that is relatively unexplored and offers insights into how restaurants with over 50 years of history are run.

"We hope that Singaporeans will continue to submit grant applications that will showcase different aspects of Singapore's unique food scene."