Edible bird's nests have become a massive export growth industry in recent years. For more than a century, these curious items were imported into Hong Kong as an exotic by-product of other Southeast Asian trade, mainly the timber trade from North Borneo (the nests were gathered there and merchants in Sandakan and other places included consignments of nests in their shipments), and then re-exported to the mainland and elsewhere. These days, most of the world's commercial bird's nests are marketed and sold onwards through shops in Hong Kong's Western district.

Two distinct types of bird, the black-nest swiftlet (Aerodramus maximus) and the white-nest swiftlet (Aerodramus fuciphagus), create edible bird's nests. The male bird spins a small, bowl-like nest from saliva, which quickly solidifies. Feathers, twigs and other items then form the rest of the nest. After the chick has flown, the nest is gathered, soaked in water, picked clean of droppings and other detritus, re-dried and then passed along the supply chain to Hong Kong.

Like shark fin and sea cucumber, edible bird's nest has little inherent flavour. To give it some taste, it is usually prepared as a sweet broth with rock sugar, dried longans, red dates, lotus seeds and other ingredients. None of these additions, however, can disguise the fact that the primary ingredient's "mouth-feel" reflects more or less what it is: a larger-than-average gobbet of slightly gritty phlegm.

Victorian traveller Isabella Bird recorded her impression of edible nests in her late-19th century book The Golden Chersonese and the Way Thither. "I had some of the gelatinous 'bird's-nest' soup, without knowing what it was," she wrote. "It is excellent; but as these nests are brought from Sumatra and are very costly, it is only a luxury of the rich."

Historically, edible bird's nests were collected from limestone karst caves in southern Thailand, northern Sumatra, the Malay peninsula and in coastal regions of Borneo. But while they remain a luxury, mass harvesting has made them more affordable. Demand for nests is such that they are now farmed across Malaysia and Indonesia. Abandoned buildings are partially sealed up, with small openings left for the birds to come and go. Tape recordings of swiftlet nesting sounds are played on a continuous loop to attract new arrivals, and food is put out to ensure that the birds don't venture too far from home.

In areas where limestone karst formations are common, such as Ipoh and the Kinta valley districts north of Kuala Lumpur, concrete blockhouses that resemble limestone caves are built to encourage nesting. As a result, there is no longer any need to go into remote areas and find birds nesting in the wild, although wild nests - like salmon - attract a higher price than the farmed variety, as they are believed to be more nutritious.

Counterfeiting of nests has become a major trade problem for Malaysia. Meanwhile, two factors contribute to Hong Kong's pre-eminence in the business: no local sales tax or customs duties on these items mean they are much cheaper than on the mainland. And Hong Kong's vastly superior consumer-protection legislation ensures the quality of nests is reasonably well guar-anteed, while proven counter-feits and adulterations can be satisfactorily dealt with through the courts.


Clarification: The observation that appeared in last week's Then & now blue bubble concerning Richard Hughes was not that of the column's author.