Sell-by date “arbitrary” on some food packaging

New research on untreated green olives has found that products with a stated shelf-life of 2-3 years can be ‘unacceptable’ long before their sell-by date. The study, published in the Journal of the Science of Food and Agriculture, looked at the growing trend towards using polyethylene pouches which are vacuum-packed, filled with brine or packed in ‘modified atmospheres’. Only the vacuum pouches gave promising results, producing a shelf-life of nearly two years, while those packed in ordinary air had a true shelf-life of only 9 months.

How ‘shelf-life’ can be worked out

The author of the study, Dr Efstathios Panagou, points out that the stated shelf-life on new packaging: “is not clearly defined…. quite arbitrary and is not supported by relevant studies”.

About a million tonnes of olives are eaten each year worldwide, and most are produced in the EU. Untreated green olives are valued for their superior flavour, but very little research has been done on the way their quality declines after packing.

Dr Panagou’s research looked at different packing methods over a six-month period, testing the olives for micro-organisms, acidity, colour and firmness. A ten-member expert panel then rated the product on smell, taste, and general acceptability.

Best results

The study looked at olives in different kinds of brine, in air, in a vacuum and in a modified atmosphere of 40% carbon dioxide, 30% nitrogen and 30% oxygen.

No harmful bacteria was found in any of the olives after six months storage at room temperature, but the overall quality of taste, smell, colour and firmness was found to be “unacceptable” in the air-packed olives and those packed in a modified atmosphere, and only “medium acceptability” in brine.

· Air: suggested shelf-life 9 months
· Modified atmosphere: suggested shelf-life 15 months
· Vacuum: suggested shelf-life 23 months.