Learn About Sulphur Dioxide in Dried Food


With Chinese New Year fast approaching, people often go shopping for traditional festive foodstuffs, including dried food items, like dried shrimps, mushrooms, scallops, tremella fuciformis (snow fungus), red dates and seeds for preparation of festive dishes.


Dried food refers to food which is processed by drying and its appearance, flavour and texture become quite different from those of fresh ones. As the process tends to dull the colour of food, making it less appealing and bringing negative impacts on sales, some food manufacturers will add a small amount of “sulphites” to food, which are a type of food additives used as bleaching agent, preservatives, preventing food from unpleasant browning and spoilage by pests. Yet, the sulphites will transform into “sulphur dioxide” during processing and traces of it remain in food as residues. Since these traces can be metabolized by the human body and discharged by way of urine, the health impacts of their residual presence in food are likely to be insignificant. Nevertheless, intake of excessive sulphur dioxide may result in dyspnoea, vomiting and diarrhoea, especially in the case of asthmatic or allergic individuals. It will accumulate in the body over time and put a heavy detoxification burden on the liver. Hence, the public should avoid, as far as practicable, excessive intake of sulphur dioxide to reduce associated health hazards.


With sulphur dioxide being water-soluble, immersing dried food in warm water can remove most of its residual presence in the food. Firstly, rinse and wash the dried food with clean water to remove the dust and impurities on its surface before immersing it in warm water (40oC to 50oC) for 20 to 30 minutes. After the food softens and swells, wash it again before cooking. The immersion method can preserve the flavour of dried food and remove residual additives in it. But do not reuse the water for immersion since it contains soluble substances which are hazardous to health.


The immersion method is not effective on reducing health hazards posed by all kinds of dried food, as in the case of sliced red dates, red seeds, candied sliced winter melon and candied kumquat, which are common treats served in the traditional candy box during Chinese New Year. These festive dried sweetmeats which are intended for direct consumption, though symbolic of auspice, may as well contain traces of sulphur dioxide in them. The public should read the table of ingredients on the label of pre-packaged dried food and candied food upon purchase to choose the ones containing the least amount of food additives. Do not buy any dried food whose colour is too bright or with a pungent smell. The best way is avoid as much processed food as possible to reduce excessive intake of sulphur dioxide and other additives.


Advice to the public:

  • Immerse dried food products in warm water thoroughly and do not reuse the water used for immersion.
  • Avoid buying dried food whose colour is too bright or unnatural, having an objectionable smell, already spoiled or mouldy.
  • Check on the variety of food additives indicated on the table of ingredients to reduce their intake.
  • Children, as well as individuals allergic to sulphur dioxide, should reduce consumption of dried food and candied food. Anyone who feels unwell after eating these food products should seek medical attention immediately.


Advice to the trade:

  • Pay attention to food safety information and food alerts issued by the Department of Food Safety. Upon knowing any recall of food products on sale on the premises, contact the Department of Food Safety and stop selling the questionable products immediately to ensure food safety and safeguard public health.