LIFESTYLE NEWS - A viral text circulating since 2008 claims that raw, leftover onions are “poisonous” and should never be kept for re-use, even in a fridge, because they are “a huge magnet for bacteria”.
According to science writer Joe Schwarcz, onions are in no sense a “magnet for bacteria”. In fact cut onions contain enzymes that produce sulphuric acid which inhibits the growth of germs. Sulfur compounds are why onions make you cry, why asparagus gives urine a weird odour and why garlic has its distinctive aroma.
Onions can become contaminated during handling, but there’s nothing about them that makes them intrinsically more susceptible to bacterial growth than any other raw vegetable.
“So unless you have sliced your onions on a contaminated cutting board, or handled them with dirty hands,” Schwarcz says, “you can safely put them in a plastic bag and store them and there will not be any bacterial contamination.”
After being cut, onions can be stored in the refrigerator for up to seven days. Store leftover halved onions wrapped tightly in plastic wrap, in a zipper-lock bag or airtight container.
Use the stored onions for cooking purposes only. Leftover onion is fine to cook with, but not ideal for using raw. Rather use fresh raw onion in salads and pickles.
Old wives’ tale
The idea that onions are a “bacteria magnet” may originate from an old wives’ tale dating back at least 500 years when it was believed that keeping bowls of raw onions around the home protected it from bubonic plague and other diseases because it absorbed the “miasma” or what was believed to be the cause of the infections.
This was long before germs were discovered. People believed that contagious diseases were spread by miasma, or poisonous air. The (false) assumption was that onions cleansed the air by absorbing harmful odours.
While false, this belief remained part of folk medicine through the 19th century claiming to ward off epidemics like smallpox, influenza and other “infectious fevers.”