The exotic secrets of Cow Street

He still goes to the kitchen every day to cook for his customers. "If you don't do it for a day you notice, if you don't do it for two days, your family notices, and if you don't do it for three days, your customers notice."

Cooking is the final step in preparing the dish, Feng says, but first you need to learn how to choose, wash and cut the tripe, and that requires one or two years' practice.

Feng is glad to see his old customers from 30 years ago now bring their sons and grandsons to eat his dishes.

"Each of these traditional snacks are irreplaceable, and I feel it's my responsibility to safeguard the flavor and pass it on."

Ma Guoqi, 76, also insists on continuing his family tradition of making spiced beef and mutton, even though he now only has a booth in a company canteen.

Ma is the sixth descendant of his family business, Yueshengzhai Ma, which was established in 1775, meaning it is a year older than the United States.

"From coal to gas tank, and now to electric cooker, we have updated the equipment we use to cook the meat, but the flavor is the same as it was generations ago," Ma says.

He now lets his son and daughter do the cooking, but has still not divulged the secret recipe of the spices yet.

"We don't have a written recipe, so it's all in my head. My father gave it to me just before he died, and he asked me to do the same.

"'We treat the meat the same way we treat our customers,' my father always told me."

Just as Ma's father impressed on him the importance of being honest in business, so it would last down the years, Ma impresses on his son the importance of being consistent with flavor.