We’ve all been there: you’re about to make a delicious sandwich, only to discover your loaf of bread has developed a suspicious green or blue patch.
The temptation is real—just cut off the offending bit and carry on, right? But is that really safe? And why does bread seem to go mouldy so quickly, especially when you’ve only just bought it?
Bread is a staple in most Australian households, but it’s also a magnet for mould. Why? Bread is soft, slightly moist, and packed with sugars and starches—basically, a five-star hotel for mould spores. Add to that our often warm and humid climate, and you’ve got the perfect conditions for mould to thrive.
Darin Detwiler, PhD, a food safety expert at Northeastern University, says bread’s vulnerability to mould makes proper storage essential for both freshness and safety.
Every time you open your bread bag, you’re exposing it to airborne spores that are everywhere—on your kitchen bench, in the air, even on your hands. Once these spores land on your bread, they can start to grow, often invisibly at first. Within a few days, those tiny spores can turn into the dreaded fuzzy patches we all recognise.
Some types of bread are more susceptible than others. Mass-produced supermarket loaves often contain preservatives that slow down mould growth, while fresh bakery or homemade breads—especially those without preservatives—can go mouldy in just a couple of days.
There are more than 1.5 million species of mould, but only a handful are likely to invade your loaf. The most common culprits include Rhizopus stolonifer (black bread mould), which starts as white fuzz before turning grey or black.
Penicillium often appears as blue-green patches, sometimes accompanied by a musty smell. Cladosporium mould is typically olive green to black in colour, while Aspergillus can come in a variety of colours, including white, yellow, green, brown, or black.
Here’s the hard truth: if you see mould on any part of your bread, the whole loaf needs to go. Cutting off the visible mould isn’t enough. Mould doesn’t just grow on the surface—it sends root-like structures (called hyphae) deep into the bread, so you can’t tell how far it’s spread just by looking.
Martin Bucknavage, MS, a senior food safety extension associate at Pennsylvania State University, emphasises that the moment any mould or discolouration appears on a slice of bread, it’s best to discard the entire loaf. ‘Once mould forms, just throw it out,’ he advises. ‘It’s just not worth it.’
Even if only one slice looks affected, spores can travel between slices, especially in pre-sliced loaves. Eating mouldy bread isn’t just unpleasant (think musty, earthy flavours), it can also be risky. Some moulds produce mycotoxins—nasty substances that can cause allergic reactions, respiratory issues, and, in rare cases, more serious health problems.
While a single accidental bite probably won’t do you much harm, it’s not worth the risk, especially for older adults or anyone with a weakened immune system. And don’t think you can just toast or microwave the mould away—heat might kill the spores, but it won’t destroy any toxins that have already formed.
The good news? With a few simple tricks, you can slow mould growth and keep your bread fresher for longer. Store supermarket bread in its original plastic bag at room temperature and seal it tightly—it’s made to last about a week.
For bakery or homemade bread, use a bread box or paper bag to let it breathe and avoid trapped moisture. Clean your bread box regularly, as mould spores can linger.
Freeze any extra slices if you won’t finish the loaf in a few days; just wrap them well to prevent freezer burn. Skip the fridge—it may slow mould, but it dries bread out.
Lastly, consider sourdough—its natural acids help it stay fresh a bit longer thanks to the lactic acid bacteria in the starter. If you’re a slow bread-eater, this might be a good option.
When it comes to mouldy bread, it’s always better to be safe than sorry. If you spot any fuzz, discolouration, or a musty smell, toss the whole loaf. With a few simple storage tweaks, you can keep your bread fresher for longer and reduce waste.
Have you got any tried-and-true tips for keeping bread fresh? Or maybe a favourite recipe for using up stale (but not mouldy!) bread? Share your thoughts and ideas in the comments below.
Also read: Freeze, thaw, refreeze? What’s safe when it comes to food storage?
I bake my own Sourdough bread and have done for many years, and it has never gone mouldy.
Wow, ronloby! Got any tips to share?
I disagree with this article. For instance in my experience supermarket bread goes mouldy in a couple of days if left in it’s plastic bag at room temperature 25C not a week as this article says.
The only way to keep mould of it for more than a few days is to either remove it from plastic and put it in something that can breathe or store it in the fridge.
In fact plastic bags are the worst thing you can use for storage of most foods where mould is a problem.
Thanks for sharing, David! I second chucking the bread into the fridge! Extends their shelf (fridge?) life as well.