Supermarkets are misleading customers by providing mixed messages over how long food can be kept once opened, according to the Women's Institute.
Research by the organisation found supermarket's "once-opened" instructions were contradictory and did not make clear whether they were recommendations around food safety, or food quality.
This is leaving consumers confused as to how long they have to use a product at home, potentially encouraging them to "needlessly" throw edible produce in the bin.
In one case, Sainsbury’s own brand sweetcorn required consumers to eat it within one day of opening, whilst a seemingly identical tin of sweetcorn from Waitrose gave consumers two days to finish the tin.
Separate research undertaken by the Daily Telegraph found a range of products including meat and soup with different "once opened" instructions in different supermarkets.
Waitrose chicken breasts are labelled "eat within two days of opening" while Sainsbury's tells consumers to eat it within 24 hours of opening. Tesco advises customers to consume the entire pack immediately after opening.
Sainsbury's canned tomato soup claims it must be eaten within 24 hours, however Waitrose and Tesco's versions of the same product say they can be left for 2 days before eating. Estimates by waste charity Wrap show extending the life of a product by just one day could result in 250,000 tonnes of food waste being avoided each year.
Last year politicians on the Environment, Food and Rural Affairs (EFRA) Committee condemned supermarkets for "pushing food people don't need" to maximize profits, as they launched an inquiry into food waste.
The Government found £16bn worth of food equivalent to £700 per household is wasted every year as a result of consumers buying it and throwing it in the bin. Since then a number of major retailers have launched camaigns to reduce food waste, although the problem of misleading "once opened" labels has been largely overlooked.
Over 5,000 WI members took part in two surveys looking at supermarket practices across the board, and found that they are potentially contributing to food waste in the home by leading customers to buy more food than they need.
Just 45pc of WI members surveyed understood that best before dates were an indicator of food quality, and 26pc did not understand that use-by dates were a marker of food safety.
Emma Holland Lindsay, head of public affairs at the Women's Institute, said: "This practice is encouraging people to needlessly say food away and is very confusing.
"We want supermarkets to extend the amount of time that consumers have to use a product in their homes by making all of their ‘once-opened’ instructions on product packaging consistent and reflective of the true full open-life of the product. All once-opened instructions should be completely removed on products where food safety is not an issue."