Just how odd? Try traditional Chinese medicine, ice, moist towelettes and even carbon dioxide.

This is despite the fact that the Islamic Religious Council of Singapore (Muis) has said some items do not need the official stamp of approval to make them acceptable for Muslims' consumption.

Ms Dewi Suratty, head of halal certification at Muis, said: 'Ice and carbon dioxide are considered halal already, but some companies do it for marketing purposes and to give assurance to their customers.'

To be considered halal, food and other products must be produced or prepared in a halal environment. This means no parts of a pig or alcohol must have been used during production. Also, meat used must come from animals slaughtered in an Islamic manner, with the windpipe and gullet severed.

The rise in popularity in halal certification will come up for discussion at a trade forum at Food and Hotel Asia, which opens today at the Singapore Expo. As an indication of the growth in this niche market, the pavilion showcasing the latest in halal products will be almost twice the size of the one in the previous show in 2006.

The number of halal-certified restaurants here has grown 10 per cent, year on year since 2000 - from 533 that year to 2,012 last year, said Muis.

Companies pay between $320 and $670 to receive or renew a halal certificate for their premises, depending on the type of business and the duration of certification.

One company which has applied for a halal certification is industrial and medical gas supplier Singapore Oxygen Air Liquide, which supplies carbon dioxide for fizzy drinks. A spokesman said the company did it at the request of a major drinks manufacturer here.

Last year, traditional Chinese medicine maker Science Arts had 19 of its products, including lingzhi and bilberry capsules, certified halal. Wet-wipes company Freshening Industries also had its line of alcohol-free moist towelettes certified last year.

It seems to be a business move that pays dividends.

Ice maker Tuck Lee, for example, has had a 5 per cent increase in sales since it had its ice products declared halal in 2000. Muslim customers now account for 20 per cent of its orders compared to 15 per cent before certification.

Globally, halal food has become a megabucks industry in recent years. This is largely because of the growth of the Middle East consumer market. Global demand for halal food products is now around $560 billion, said Muis.

In Singapore, parallel growth in affluence among Muslim consumers has contributed to the market's growth as well.

Ms Dewi said: 'There is definitely high demand from Muslims who are more adventurous and well travelled and who want more choice in dining and food products.'