When you cook food at home, you know you have two hours — arguably four if you really want to push it — to get your food out of the room-temperature air and into your belly. Any longer, and that plate of chicken salad is a bacterial brouhaha. But if you're picnicking in 30C+ weather, food goes bad faster — a lot faster.
In the sweltering heat, you only have one hour to work with. That means your fruit salad should stay in the cooler until dinnertime, and your just-cooked barbecue shouldn't sit out on the picnic table forever, either.
Food safety expert Ben Chapman ran the numbers on the one-hour rule, expecting it to be overly cautious. But it turns out that Salmonella bacteria easily multiply tenfold in a little over an hour at 32C. Another common food poisoning germ, Staphylococcus aureus, takes a bit longer — one and a half to two hours.
Either way, if you were using the same two-hour rule that applies indoors, you'd have a chance of making yourself sick.
Got into Combase to look at some growth predictions for food held out at a cookout on a hot day thanks to @bugcounter. Here’s what Salmonella looks like at 90F/32C. 1 Log growth in a little over an hour (w/ no lag, assuming it’s something like potato salad starting at room temp) pic.twitter.com/Mlk11T9upX
— Ben Chapman (@benjaminchapman) May 23, 2018
How to Avoid Hot-Weather Food Poisoning
First, know which foods are the ones prone to going bad in the heat. Spoiler: it's most of them. That includes cooked vegetables, cooked grain dishes (like rice), and meats. Low-acid fruits, like cantaloupe, also need to stay chilled if they will be on the table a while.
Foods that are usually safe include things that are dry-ish, like bread, and condiments like salsa or relish that are very acidic. As soon as you put them on a non-acidic food, though — like vinegar dressing on pasta salad — all bets are off. The vinegar might slow down bacterial growth a little, but not enough to be worth taking chances.
Here's what Chapman recommends for picnicking without making yourself and others sick:
- Keep food out of direct sunlight. It warms up even faster that way. (Bacteria grow fastest around 35C degrees or so — about the same as our internal body temperature.)
- Plan ahead. If the meat comes off the grill but people aren't ready to eat, take it inside (if you're in the backyard) or pop it into the esky. Keep an eye on the time.
- Wash your damn hands. (My wording, not his.) A lot of the bacteria that cause food poisoning are ones we carry around on our hands. They either live on us naturally (like Staph. aureus) or can be carried from other foods (like E. coli, which may come free with your mince).
This might disrupt your usual cookout routine, but it's all very doable with a little planning ahead. If you're barbecuing away from home, book a picnic pavilion near the toilets and pack an esky and a bunch of ice to transport your goodies and to take home leftovers. You'll be glad you did, when you're heading home sans food poisoning.