Food safety: Can you really trust the five-second rule and the sniff test?

By The Conversation|

You might be putting too much trust in these time-honoured food safety tests

You might be putting too much trust in these time-honoured food safety tests, writes CSIRO food microbiologist Cathy Moir for The Conversation.

There are many rules in food safety lore, some that have a basis in fact, and some that are purely grounded in convenience. But it’s important to look at the evidence to see which category common rules fall under.

1. The sniff test

Often when a food has spoiled, it will smell bad. This leads many to believe “no stench = OK to eat”. But this isn’t always the case. The microorganisms (bacteria, yeasts and moulds) that spoil food by making it smelly, slimy or mouldy might not give you food poisoning.

But pathogenic (disease-causing) bacteria, such as salmonella, campylobacter, E.coli and listeria, which do make people sick, don’t always cause obvious changes in food when they grow. Sometimes simply being present at low numbers and then consumed is enough to result in illness.

RELATED: Why you can't trust the sniff test for spotting unsafe food

Having said that, this isn’t an invitation to consume obviously spoiled food. Spoilage is a good indicator food has been left too long and “bad” microorganisms, including pathogens, may also have grown.

In order to steer clear of nasty bugs in food, observe “use by” dates, refrigerate foods that need to be kept cold (this slows down the microbes), cook foods properly (this kills the microbes) and prevent contact and cross contamination between ready-to-eat foods such as salads, with raw food such as meat that still needs to be cooked.

2. The five-second rule

Whether it’s one, three, five seconds or some other number, we’ve all heard some version of this call when someone has dropped food on the floor. But is it true harmful bacteria need a few seconds to hitch a ride on your dropped slice of pizza?


  • time is not necessarily of the essence as microorganisms from one surface can instantaneously contaminate another. But it’s true the longer contact time the more contamination can occur.


  • the weakest microbial transfer occurred when food was dropped on to carpet compared to stainless steel, and tile in particular. The authors hypothesised bacteria attaches better to carpet as it’s more absorbent, meaning it’s less likely to transfer to the food.


