What’s the difference between “use by”, “best before”, “expiry date”?
“Use by” dates are stricter than other date markings as they can refer to the safety of the food, particularly for infant formula, or fresh produce like meat, fish and poultry, a Singapore Institute of Technology associate professor said.
“These items should, as much as possible, be consumed by the dates indicated as they tend to turn bad, spoil or (become) rancid at a quicker rate than other types of food,” said Dr Siti Noorbaiyah Abdul Malek, an expert in food safety and quality.
“Best before” dates, on the other hand, indicate how long food will last before it starts to lose its quality.
“For instance, a packet of biscuits may be found soft instead of crisp after the indicated ‘best before’ date, but they can still (be) edible,” Dr Siti said.
But this is provided that the food was stored properly, under the right temperature and environment, she added.
The Singapore Food Manufacturers’ Association said a “best before” date is akin to a recommendation based on the manufacturer’s experience. After the date, the food could still be edible but might have lost its texture or flavour.
“Expire by” and “use by” date marks can be taken as “hard deadlines”, after which a product might be contaminated, said the association’s IT director Ang Khim Whee, who also sits in Enterprise Singapore’s Food Standards Committee and the National Codex Committee.
How do manufacturers determine such dates?
Through lab tests, experts said. According to Mr Ang, the lab will test five different parameters, including total plate count and escherichia coli (E. coli) bacteria.
Total plate count measures the bacteria count of the product over time, said Mr Ang. A small sample of the product is diluted, then placed in a petri dish and tested.
Dr Siti said manufacturers may also conduct shelf-life studies on products through a real-time or accelerated approach. For real-time testing, manufacturers keep food at storage conditions specified on their label and evaluate the food intermittently to see how it has deteriorated throughout the study.
“When the extent of deterioration has compromised the quality of the food … they can then indicate the shelf life of the food,” she said.
In the accelerated approach, manufacturers keep food at elevated temperatures to speed up deterioration.
“Similarly, once they determine that the quality of the food has been compromised, they can extrapolate the shelf life based on certain mathematical models that can be used to predict results.”
Food manufacturers usually choose “best before” dates conservatively well before the time food would spoil and become inedible, Dr Siti said.