Don't Let Leftovers Cool Too Much

Cooked too much and want to store some of your food in the fridge for later consumption, but aren't sure whether you should cool it first? The Conversation examines the science of food storage (and food poisoning) and offers up a simple suggestion: if in any doubt, freeze it as soon as the steam stops rising. If you leave food to cool for too long, the risk of bacterial nasties increases rapidly.

Picture by rfduck

University of Newcastle nutrition professor Clare Collins explains the process:

As cooked food drops to 60°C or below, bacteria that have survived the cooking will start to multiply until the food cools down to five degrees. The longer the food is left to cool, the longer the bacteria – which causes food poisoning – has to multiply.

If you're super-paranoid, you can use a food thermometer to measure the internal temperature. But in the real world, that's a somewhat unlikely scenario, and this advice seems more useful:

If you intend to store cooked foods to eat later, you can cool it on a bench as long as the temperature doesn’t drop below 60°C. This is roughly when the steam stops rising. You can keep cooked meals safely in the fridge for a few days, but if you want to keep it for longer, put it straight into the freezer.

Time of cooling aside, it's often tempting to pop leftovers in the fridge, because that way they'll be easier to reheat (and you can potentially eat them cold). But if you want to reduce the risk of food poisoning, let your food cool just to non-steaming point, and then freeze. If you've got a microwave, getting your food back to a heated state won't be any trouble. Another useful pointer from the article: always defrost in the fridge. Defrosting on the bench also increases the risk of bacteria multiplying as the food sees its temperature rise.

Monday’s medical myth: leave leftovers to cool before refrigerating [The Conversation]


Comments

    Oh great, so the tip I read about leaving it to get to room temperature is wrong?
    However, if its something to be microwaved later, surely the microwave will kill off that bacteria anyway, as long as it's cooked well?

    I read that chicken or turkey stuffing is really bad if left for a while as it stays lukewarm for a long time and may be the last part to get cold in the fridge.
    Also don't eat leftover seafood at all.
    Barbecues can be bad for latecommers who eat leftover snags from the cooling barbie.

    Microwave kills bacteria when reheating anyway.

    Reheating or cooking to above 75 degrees kills most bacteria
    Above 60 degrees bacteria will not grow.
    Above 5 and below 60 is when they grow like crazy
    Below five is best for cold storage and they are only growing slowly
    Frozen - bacteria don't grow but chemical reactions still occur
    Below minus 25 is when chemical reactions stop, but the quality is probably effected due to it being frozen.

    SOOOOO...

    Cooling food from cooked/reheated (75 degrees) is safest when the food is cooled to below 5 degrees within 4-6 hours.

    Note: some bacteria Thermophiles can grow at higher/hot temps and Mesophiles grow at fridge/cold temps (such as Lysteria!).

    Once it stops steaming chuck it in the fridge covered.
    To cool it quicker portion into smaller containers.

    Hi. I cooked a casserole between 9pm-11pm and left it to cool down
    in the oven over night before refrigerating in the morning. I had
    some reheated the next day at lunch and a few hours later, I had
    the runs. I'm usually good at reheating food. Could it be the junk
    food I ate that day or have I created problems letting cool down
    too slowly? Many thanks.

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