Long term sell-by dates on some packaged foods are not justified, research has suggested.
Tests were run on packaged olives
Olives with a claimed shelf-life of up to three years can be "unacceptable" to eat long before, agricultural researchers in Greece found.
They said the move towards plastic packaging has led to some "arbitrary" sell by dates.
Food manufacturers said standards were high and firms were complying with guidelines and regulations.
About 10 million tonnes of olives are consumed worldwide each year, most of which are produced in Europe.
There is a growing trend towards using polyethylene pouches which are either vacuum-packed, filled with brine, air, or packed in a combination of gases.
Suggested shelf-life for olives
Packed in air - nine months
Packed in a "modified atmosphere" - 15 months
Vacuum-packed - 23 months
The study, published in the Journal of the Science of Food and Agriculture, suggested only vacuum pouches could justify a claim to a shelf-life of almost two years, while olives packed in air were only good for nine months.
Olives in Greece were tested over a six-month period for micro-organisms, acidity, colour and firmness.
A ten-member panel then rated the product on smell, taste, and general acceptability.
No harmful bacteria were found in any of the olives but the overall quality was found to be "unacceptable" in the air-packed olives and those in a "modified atmosphere" of 40% carbon dioxide, 30% nitrogen and 30% oxygen.
Those in brine were found to be of "medium acceptability".
Dr Efstathios Panagou, of the National Agricultural Research Foundation in Athens, led the research.
He said: "The shelf-life of these products is not yet clearly defined, although the majority of Greek industries state a shelf-life of two to three years on the labels based on the fact that olives are a fermented product of high quality.
"However, this period is quite arbitrary and is not supported by relevant studies."
The National Food Processors Association (NFPA) in the US said it was the manufacturer's responsibility to determine the shelf life of their product.
Whether the researchers' findings agreed with the claims of the manufacturers "would depend on the storage conditions they used," said Allen Matthys, vice-president for federal and state regulations at the NFPA.
Regulators would be keeping a check on the shelf-life claimed by the manufacturers and would intervene if they were not correct, Mr Matthys added.
A spokeswoman for the Food and Drink Federation in the UK said it had information on short-term chilled foods which were vacuum packed (VP) or modified atmosphere products (MAP), but not on those with a long shelf-life.
However, she added: "In general, for a longer shelf-life, products will need to meet specific controlling factors or manufacturers will need to undertake a risk assessment to determine the maximum safe shelf-life.
"The food and drink manufacturing industry has maintained an excellent safety record in respect of VP and MAP chilled foods and is satisfied with the current industry code of practice."
The UK's Food Standards Agency said a "use by" or "best before" date was a legal requirement but shops and manufacturers could decide whether to add a "sell by" or "display until" date.
A spokeswoman added: "The sell by date is more for quality, it is the use by date that is more important as it refers to the safety of the food."