Cooking in bulk is cost effective, saves time and reduces food waste, however extra care needs to be taken when handling large amounts of food.

Stomach flu is prevalent during winter but it's not just the norovirus infection that can cause a bout of gastroenteritis.

Cooking warming winter casseroles and soups in bulk can be a health hazard if not handled properly, food safety experts warn.

Rachelle Williams, chair of the Food Safety Information Council, says if large amounts of food are left to cool slowly bacteria will find a way to grow, even in cooler months, to produce dangerous toxins that can't be destroyed through further cooking.

The main thing to remember, she says, is to divide food that won't be eaten immediately into small portions.

"Do this as soon as the food has stopped steaming and refrigerate or freeze straight away," she says.

Portion size is equally important and Ms Williams recommends a takeaway size container.

"The food will cool quickest in small containers which will reduce the risk of the bacteria growing and producing toxins," she said.

Refrigerated leftovers should be used within two to three days.

When slow cooking, the temperature should be at 60 degrees Celsius or above.

"Cooking in bulk is cost effective, saves time and reduces food waste. However, we need to be extra careful handling these large amounts of food," Ms Williams said.