Asked by: Tony Ferrer, High Wycombe
Not much. Numerous studies have shown that some bacteria is transferred to food as soon as it touches the floor. Bacteria don’t sense food dropped nearby and then home in on it – they get glued on by moisture and grease when the food falls on top of them.
A 2014 undergraduate study at Aston University found that the amount of bacteria was higher on food left on the floor for 30 seconds, compared with food that was picked up quickly. But this research wasn’t published in a peer-reviewed journal, so it isn’t clear how significant these results are. Another unpublished study at Manchester Metropolitan University found that very sweet foods like jam are actually less likely to get contaminated, because bacteria can’t grow in high concentrations of sugar.
But while the exact proportion of floor bacteria that gets transferred to dropped food is interesting, it doesn’t have very much bearing on how safe the food is to eat. We swim through a soup of bacteria everywhere we go. Bacteria are on every surface and we constantly pick them up with every touch. The hand that picks up your sandwich is probably just as contaminated as the kitchen counter or the floor. We are evolved to cope with these everyday germs with powerful stomach acid and an immune system to kill them off. Undercooking your chicken will give you food poisoning. Eating a chicken nugget off the kitchen floor probably won’t.