How long does tomato sauce, mustard and mayonnaise really last?

Ketchup lasts about 3 months in the fridge . Photo / Getty Images

Most of us know when to chuck out meat, fish and fresh vegetables - but it's much harder to know when sauces are past their use-by date.

Now a new guide definitively spells out when our favourite condiments need to be thrown in the bin- as well as settling a fierce social media debate, reported the Daily Mail.

But the new guide, by Good Housekeeping, reveals that you should keep it in the fridge once it's been opened after all - but only for three months before it needs to be thrown away.

According to the guide apple and cranberry sauces have the shortest shelf life at only one month, while soy sauce keeps for a year and malt vinegar lasts indefinitely.

Those other sauces in your pantry

• Worcestershire sauce- 1 year in the cupboard
• Soy sauce- 1 year in the cupboard
• Sesame oil- 6 months in the cupboard
• Hot chilli sauce- 6 months in the fridge
• Sweet chilli sauce- 6 months in the fridge
Mint sauce - 2 months in the fridge
BBQ sauce- 6 months in the fridge

Good Housekeeping have also settled the debate once and for all about where these sauces should be stored.

Most of them should be kept in the fridge after they've been opened and the seal has been broken - including ketchup.

This corresponds to advice given to the Daily Mail by microbiologist for Initial Hygiene Dr Peter Barratt, who said that modern ketchup contains a lot less salt (which preserves the condiment) than it used to and therefore needs to be kept in the fridge after opening.

Ketchup should be kept in the fridge after opening. Photo / Getty Images

Before then the sauces can safely be kept in the cupboard.

Yet a handful of the sauces can be kept in the cupboard even after they've been opened.

These include: malt vinegar, virgin olive oil, Worcestershire sauce, soy sauce and sesame oil.

It follows a social media row earlier this year which raged for several days online about whether ketchup belongs in the fridge or the pantry before it's been opened, as well as once the seal has been broken.

Asda - one of Britain's "big four" supermarkets - started refrigerating some of its bottles while keeping others on shelves to see which one customers prefer.