Three chefs and a registered nutritionist have given the same verdict on where to store mayonnaise after opening: it must go in the fridge. The consensus was shared exclusively with us, following a similar agreement on ketchup storage.
Chefs' unanimous verdict
Chefs Mike Reid, Jeremy Pang, and Nima Safaei, along with Lily Keeling, Registered Nutritionist and Recipe Development Manager at Green Chef, all agreed that opened mayonnaise should be refrigerated. Jeremy explained: "Mayo - a definitely no go outside of the fridge! My kids call it 'egg sauce' and you wouldn't just leave 1/2 cracked raw eggs lying around in a cupboard."
Mike echoed this, saying: "Mayo - the one everyone panics about for entirely the wrong reasons. Shop-bought and unopened? Cupboard, genuinely - it's sold off a shelf, not a chiller. Once opened, fridge. Homemade, with raw yolks, is the only one to be strict about, fridge, and eat within a couple of days. And that classic 'the mayo turned at the picnic' line is a myth - it's far too acidic for bugs to enjoy." He added: "Nine times out of ten it's the chicken cooking in the sun next to it that gets you, not the mayo."
Food safety and quality
Nima stated that mayonnaise "should always be refrigerated after opening, regardless of whether it's homemade or shop-bought". He explained that because it is egg-based, it's best to keep it "consistently cold for both quality and food safety". He also warned against leaving it out during gatherings: "One mistake people make is leaving the jar out on the table throughout a barbecue or family meal. If mayonnaise sits at room temperature for too long, particularly on a hot day, it's best to discard any leftovers rather than return them to the fridge."
Lily Keeling said: "Mayo is one I'd always keep in the fridge once it's been opened. When unopened, it's fine in a cupboard, but I always keep it in the fridge. It's made with mostly eggs and oil, and can lose its freshness if it's left out at room temperature for too long."
Brand guidance
Hellmann's, widely recognised as the world's most prominent mayonnaise brand, also recommends refrigerating after opening. Its guidance says: before opening, keep unopened jars in a cool, dark place like a pantry or cupboard, away from sunlight and heat. Once opened, refrigerate immediately, ideally in the door to avoid freezing. Avoid freezing altogether, as it breaks the emulsion. Don't leave it out for more than four hours, and always use clean utensils to prevent introducing bacteria.
Heinz also told us: "Our mayonnaise is the same storage as the ketchup, once opened this has to be kept in the fridge. This is printed on both our ketchup and mayonnaise bottles."
