Q: By mistake, I left meatballs in a tomato sauce overnight in the microwave. Would they still be safe to eat the next day? Absolutely not. Sorry. Two hours usually is the limit for unrefrigerated perishable food. But in the case of the meatballs in the microwave, you had even less time because they probably were heated and then left in that warm, moist environment. They probably became dangerously compromised by bacteria within an hour.
When you're trying to decide whether something is safe to eat, remember the rule "time and temperature equals bacteria growth." Like all living organisms, bacteria need the right conditions to grow, and they need time to increase their numbers to the point where there are enough bacteria to make you sick when you eat the food.
Usually, you have two hours between when the food is oven-hot or refrigerator-cold before the bacteria can multiply to the point of making you sick. In the summer, when the temperature is higher, or in a warm place such as a microwave or oven that was hot and then cooled off, the bacteria can grow even faster. So in summer, you should reduce the two-hour rule to one hour to compensate.
Charlotte Observer Food editor Kathleen Purvis answers questions about food and cooking. Send questions to firstname.lastname@example.org.