Your child may start thinking about lunch during math class. But you should think about it when it's packed, said a University of Georgia scientist.

"Food safety for a packed lunch depends on how it's packed and what is packed," saidÿ Connie Crawley, an Extension Service nutrition and health specialist with the UGA College of Family and Consumer Sciences. "It's not hard to keep packed lunches safe. But it takes some thought and preparation."

Crawley said the first step to packing safe lunches is choosing a well-insulated bag or box. The most important thing in food safety, she said, is keeping cold foods cold and hot foods hot, no matter what the meal.

Keep cold foods at or below 40 degrees Fahrenheit and hot foods at or above 140. The danger zone is between those two temperatures, she said. If food stays at room temperature for two hours, it's very risky to eat it.

The temperatures at which we're comfortable in our homes and offices are also perfect for bacteria that can cause. Common food-borne illnesses are caused by Staphylococci, Salmonella, Campylobacter and other bacteria.

Many children prefer their foods cold, so keeping food chilled is often more of a concern than keeping it hot. Hot food also raises concerns for the child's ability to open the container and serve himself safely.

Cleanliness during lunch preparation is important, too, Crawley said. "It's almost more important to be careful while you pack a lunch, since the potential is greater for the growth of bacteria before the lunch is eaten," she said. "Of course, the bacteria have to be present to grow. But there's no point in taking chances.

"Bacteria can be introduced while you pack the lunch," she said. "Don't leave food out at room temperature too long before you pack it. Keep the cold foods to be packed in the lunch box refrigerated until the child is ready to leave for school."

Choosing the food for lunch is another important step. Some foods are more perishable than others, Crawley said, and should be treated as such. Pack more perishable foods close to a cold source in the bag or box.

"Blue ice" packs or frozen juice bags or boxes provide a good cold source that can keep perishable foods safe until lunchtime. Frozen juice drinks will usually thaw in time to go with lunch, so they won't take up extra space in the bag, Crawley said.

A good rule of thumb about safely packing lunches is to pack it however you bought it. "If it was refrigerated, keep it cold," Crawley said. "Shelf- stable items may taste better cold but won't spoil if they sit at room temperature."

Talk with your child about what foods she likes for lunch. Then pack meals she prefers.

Peanut-butter-and-jelly is a standard that doesn't need to stay cold, unless that's how she wants it. Cut-up veggies and fresh fruit are favorites that aren't perishable short-term. They provide nutrition kids need in a way they like.

But choose new lunch foods carefully. "Practice lunch at home, especially if you start packing cans of shelf-stable pudding or cut-up fruit," Crawley said. "Then you'll know if your child can safely and easily open the container."