I have been sent a couple of emails regarding the risk of food poisoning from using leftover onions. It "seems" that cutting open and then storing leftover onions in the fridge to be used can cause food poisoning due to onions being a magnet for bacteria. No matter how well stored they are or how short a time they are kept for- once you cut an onion either use it immediately or throw out. Does anyone else know if this is in fact correct or just another email myth? Seems such a shame to throw out - but it could explain stomach upsets for no other known reason. Be interested in any comments please.
Cheers - Sandy

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Looks to be a myth. I had a search and found plenty of information saying onions are not particularly good breeding grounds for bacteria.
Thanks Nicholas, that is the problem with internet/emails - anyone can send emails claiming research on basically anything these days - and do so. So many people stopped eating/drinking all sorts of things due to that. Always pays to double check.
Interesting ??never heard that one before not to say its a myth or anything,maybe some people are susceptible than others because we often have an cut onion in fridge and have never experienced any upsets.
Thanks for the responses, looks like another urban myth. Guess it is a timely reminder to always cover and keep cut foods safe in the fridge as I have always done. Having dinner with a dietitian friend tonight so will discuss this with her.

I have copied the contents of one of the emails that led me to ask the question in the first instance. Thanks again people for your replies.


I have used an onion which has been left in the fridge, and sometimes I don't use a whole one at one time, so save the other half for later.

Now with this info, I have changed my mind.....will buy smaller onions in the future.

I had the wonderful privilege of touring Mullins Food Products, Makers of mayonnaise. Mullins is huge, and is owned by 11 brothers and sisters in the Mullins family. My friend, Jeanne, is the CEO.

Questions about food poisoning came up, and I wanted to share what I learned from a chemist.

The guy who gave us our tour is named Ed. He's one of the brothers Ed is a chemistry expert and is involved in developing most of the sauce formula.. He's even developed sauce formula for McDonald's.

Keep in mind that Ed is a food chemistry whiz. During the tour, someone asked if we really needed to worry about mayonnaise. People are always worried that mayonnaise will spoil. Ed's answer will surprise you. Ed said that all commercially- made Mayo is completely safe.

"It doesn't even have to be refrigerated. No harm in refrigerating it, but it's not really necessary." He explained that the pH in mayonnaise is set at a point that bacteria could not survive in that environment. He then talked about the quaint essential picnic, with the bowl of potato salad
sitting on the table and how everyone blames the mayonnaise when someone gets sick.

Ed says that when food poisoning is reported, the first thing the officials look for is when the 'victim' last ate ONIONS and where those onions came from (in the potato salad?). Ed says it's not the mayonnaise (as long as it's not homemade Mayo) that spoils in the outdoors. It's probably the onions, and if not the onions, it's the POTATOES.

He explained, onions are a huge magnet for bacteria, especially uncooked onions. You should never plan to keep a portion of a sliced onion. He says it's not even safe if you put it in a zip-lock bag and put it in your refrigerator.

It's already contaminated enough just by being cut open and out for a bit, that it can be a danger to you (and doubly watch out for those onions you put in your hotdogs at the baseball park!)

Ed says if you take the leftover onion and cook it like crazy you'll probably be okay, but if you slice that leftover onion and put on your sandwich, you're asking for trouble. Both the onions and the moist potato in a potato salad, will attract and grow bacteria faster than any commercial mayonnaise will even begin to break down.

So, how's that for news? Take it for what you will. I (the author) am going to be very careful about my onions from now on. For some reason, I see a lot of credibility coming from a chemist and a company that produces millions of pounds of mayonnaise every year.'

Also, dogs should never eat onions. Their stomachs cannot metabolize onions .....

Please remember it is dangerous to cut onions and try to use it to cook the next day, it becomes highly poisonous for even a single night and creates Toxic bacteria which may cause Adverse Stomach infections because of excess Bile secretions and even Food poisoning.
I have kept onions diced in the fridge for as long as a week and never had a problem. Sometimes myths like this are started to enhance "planned obselescence", lik saying makeup over a year old can kill you, so be careful.

I've cured bacterial infections with onions
I agree Jen,i think the problem is with so many people today is they tend to live there life's been excessively over paranoid of all the bacteria's around us, so much so that they have made there living environments and food preparation areas overly sterile,these are the people that maybe are being affected by left over onions,so then the call goes out from the health authorities that everyone needs to be aware of onions when the onion's not the cause.

Jen Stotland said:
I have kept onions diced in the fridge for as long as a week and never had a problem. Sometimes myths like this are started to enhance "planned obselescence", lik saying makeup over a year old can kill you, so be careful.
I've cured bacterial infections with onions
I have enjoyed all the responses to my query - thanks all. Yes Richard - you and Jen make sound sense. The problems in the past is that people take these sort of statements as gospel and don't bother checking for themselves. With Internet availability people are slowly starting to question such research statements and who in fact pays for such research. This time next year "latest research" could be saying eat more onions! So, in the meanwhile for lunch today is a cheese, tomato and onion sandwhich. Cheers
That's true Sandy look at the tomato,the English didn't eat it for 200 years because the church told them not to for been poisonous,even though the French at the time where.
Problem is there so many wife's tales about when it comes to gardening



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