It’s a habit many of us fall into, despite knowing better. I’ve just taken out some sliced chicken from the fridge, intending to make sandwiches. While the chicken is still within its use-by date, doubt lingers. Someone in the household has hastily opened the packaging, and the slices have been exposed in the fridge for a few days. Curious about the chicken’s edibility, I resort to the familiar sniff test, hoping for some reassurance about its freshness.
The irony is that I should know better, being a microbiologist well aware that the harmful microbes I worry about causing illness have no discernible smell. Yet there I am, attempting to bolster my confidence with the age-old sniff test.
It’s true that certain microbes emit odors during their growth. Think of the pleasant aroma of yeast in freshly baked bread, in stark contrast to the less pleasant odors produced by microbes in the form of flatulence or bad breath.
These odors arise as microbial populations flourish and increase – their metabolic processes converting carbon and other elements into energy sources or building blocks for their cellular structures. However, the microbes primarily linked to foodborne illnesses, such as Listeria and Salmonella, are virtually impossible to detect using the sniff test.
Even if present, and fortunately, the risk is relatively low, these bacteria would likely exist in such minimal quantities in the food that any metabolic activity (and hence odor emission) would remain imperceptible to our noses.
Furthermore, any potential scent of Listeria would be indistinguishable from the subtle odors generated by more abundant microbial species commonly found on our foods – species that pose no health risks.
Sure, there’s a minute chance that Listeria might be present in the smoked salmon I bought from the coastal smokehouse last week. However, there’s absolutely no way my sense of smell can distinguish any trace of Listeria amidst the delightful aromas of dill, salt, and smoke that define the product.
Back to assembling my sandwich. The odds of detecting Salmonella on the tomato I plucked from the fridge’s produce drawer are even slimmer – even if I possessed superhuman Salmonella-sensing abilities, which I don’t. If this pathogen were ever present on the tomato, it likely entered through contaminated water during growth, residing within the tomato and therefore impossible to smell.
However, it is feasible to identify food spoilage – another outcome of microbial activity as they break down food left too long or stored incorrectly. This is precisely why the sniff test is more suitable for discerning spoiled milk, minimizing food waste rather than discarding milk that might still be safe. And for some foods – consider the microbial contribution to the finest cheeses – having an aroma is a culinary characteristic.
While my wife may disagree about the aromatic appeal of certain fermented foods, like kimchi, and has banned them from our home, such foods are far from spoiled and should not be discarded. For other items, such as fresh produce or milk, I do take note of any hints of spoilage odor, using them as a reminder to store those foods better in the future or reduce consumption if I’m not consuming them promptly.
I also acknowledge that some causes of foodborne illnesses remain unknown. While bacterial contaminants such as Campylobacter or other mentioned microbes are responsible for many cases of illness, there are as many cases where the source remains unidentified. However, progress is being made, with scientists developing more precise tools than our noses to detect foodborne pathogens.
So, when concerned about foodborne illness, it’s best to channel energy into proper storage and correct cooking temperatures rather than relying on the nose to detect pathogens. I wouldn’t even trust my nose to differentiate between a cabernet and a shiraz, let alone Campylobacter and Salmonella.