The No. 1 rule at picnics?

Only eat food that is the temperature it’s intended to be. In other words, if either the potato salad or the chili is lukewarm, it’s best to scoop up something else.

Beth Grossman is a registered dietician and for the past 10 years has worked as the contract food safety inspector for Natick. She also does inspections in Maynard, Hudson and Wayland.

She said outdoor food season can be fun and safe, but there are some definite rules to live by if you want to avoid an apocalyptic post-picnic situation.

“What we’re trying to avoid is keeping food in the danger zone for pathogen growth,” Grossman said, explaining that when food reaches any temperature between 40 degrees and 140 degrees, it creates a prime environment for the rapid growth of bacteria, viruses and even spores.

But prevention begins well before the food makes it to the picnic table.

“It starts when you’re purchasing food,” Grossman said. “Buy refrigerated and frozen foods last.” In addition, she recommended keeping meat wrapped in a plastic bag and stored on the lowest shelf of the refrigerator in order to avoid possible drips contaminating other food in the fridge.

Proper pre-prep storage is just the beginning. Grossman offered the following tips for preparation through serving.

Preparing the food

• “Hand washing before you prepare food is crucial.”
• Wash all produce, especially melons like honeydew and cantaloupe. Melons are unlike other fruits and veggies in that they do provide an environment for pathogen growth.
• Rinse starches like pasta and potatoes in very cold water. “It isn’t the mayonnaise really [in potato or pasta salad]. It’s the cooked starches really that need to be kept cold.”
• Cook meat to the appropriate temperature: 165 degrees for chicken and 155-160 degrees for burgers.
• Prepare hot, dense foods like chili on the day of the picnic and “serve it piping hot.” 
• If you must prepare hot foods ahead of time, cool them in a sink of ice water before storing them in the fridge. Hot foods in the refrigerator can heat up the fridge and create an unsafe environment for other foods.

Serving the food

• If headed outside on a hot day, serve foods a little bit at a time and keep additional portions refrigerated or on the heat (depending on the food).
• “If it’s 90 degrees outside, I wouldn’t keep it out for longer than an hour.” 
• Consider serving cold foods from tabletop food coolers that rest under and around service dishes and are full of ice.

Perhaps the best rule of thumb is, “If in doubt, throw it out,” but if you need an additional reminder, check out “Who Left the Food Out,” a catchy tune from the UCDavis FoodSafe site.