1. How Microwaves Cook Food

Microwave ovens emit non-ionizing electromagnetic waves that cause water, fat, and sugar molecules in food to vibrate rapidly. This friction generates internal heat, which spreads outward via conduction and convection. Although many people believe microwaves cook food from the inside out, they actually only penetrate the outer layer (about 1–1.5 cm); the inner parts cook as heat travels inward.

2. Power Levels and Wattage

Microwaves don’t cook at “low heat” like stovetops. Instead, they pulse on and off to reach lower power settings. For example, a 50% setting means the magnetron cycles on half the time. Lower power settings are ideal for defrosting or cooking delicate foods evenly. Wattage affects speed—microwaves with higher wattage (e.g., 1000–1200 W) cook faster but may increase the risk of uneven heating if not used properly.

3. Uneven Heating and Cold Spots

Microwaves can cause cold spots, especially in thick or dense foods. These spots may allow harmful bacteria to survive. To reduce risk:

• Rotate and stir food halfway through heating.
• Cover food loosely to trap steam for more even heating.
• Use a food thermometer to check multiple parts of the food.

4. Importance of Standing Time

“Standing time” is the period after cooking when food remains outside the microwave but continues to cook due to retained heat. This step is crucial—it helps even out temperature and ensures bacteria are destroyed. Standing time of 2–3 minutes is typically sufficient.

5. Internal Temperature Guidelines

To ensure food is safe, use a thermometer to confirm it has reached the appropriate internal temperature. Poultry, leftovers, and casseroles should be at least 165°F (74°C). Stirring and checking in several areas is key because surface appearance may not reflect safety.

6. Avoid Partial Cooking

Microwaving food only partially (e.g., just to “preheat” or “soften” meat) is not safe. Bacteria may not be killed if food is not fully cooked in one continuous session. Always finish cooking immediately after defrosting or heating.

7. Stuffed Poultry in Microwaves

It is not recommended to cook stuffed poultry in a microwave oven. The stuffing often doesn’t reach safe internal temperatures fast enough, which can allow harmful bacteria to multiply.

8. Thawing Frozen Food

Use the defrost setting or 30–50% power to thaw frozen food evenly. Always remove plastic or foam trays before microwaving. Rotate food halfway through thawing, and cook it immediately afterward—never refreeze thawed items.

9. Reheating Cooked Food

When reheating leftovers, ensure even heating by:

• Covering with a microwave-safe lid or wrap (vented).
• Stirring or rotating midway.
• Checking that food steams and reaches at least 165°F (74°C) throughout.

10. Safe Containers and Wraps

Always use microwave-safe containers such as:

• Glass or ceramic dishes.
• BPA-free plastic labeled “microwave-safe.”
• Microwave-safe plastic wrap (not touching the food), parchment paper, or wax paper.

Avoid using:

• Aluminum foil (unless specifically allowed and placed far from oven walls).
• Metal pans or utensils.
• Styrofoam trays.
• Thin plastic containers not labeled for microwave use.

To test if a container is safe: Microwave it with a cup of water for one minute. If the container stays cool and the water heats, it’s generally safe.

11. Can You Use Aluminum Foil?

Aluminum foil can reflect microwaves and cause sparks (arcing). If absolutely necessary, use only small, smooth strips to shield parts of the food (e.g., wing tips), and keep foil at least one inch away from oven walls.

12. Are Microwaves Safe for Health?

Yes. Microwaves use non-ionizing radiation, which does not make food radioactive. The ovens are designed with safety features like shielding and interlocks to prevent radiation leakage. They’re safe for use unless damaged or altered.

13. Arcing, Superheating, and Other Hazards

• Arcing occurs when metal touches the oven walls, producing sparks. Stop the microwave immediately if this happens.
• Superheating happens when liquids heat beyond their boiling point and erupt unexpectedly. Prevent this by placing a wooden stick or spoon in the liquid and avoiding excessive heating.
• Microwave burns are thermal injuries from hot containers, steam, or erupting foods. Handle heated food with care.

14. Cleaning the Microwave Oven

• Clean spills immediately with mild soap and a soft cloth.
• For tougher stains or odors, microwave a bowl of water with lemon juice for 3–5 minutes. The steam will loosen debris, making it easy to wipe clean.
• Never use abrasive cleaners or scrubbers.

Final Tips for Safe Microwave Use

• Always follow manufacturer instructions.
• Use microwave-safe containers.
• Stir and rotate food for even cooking.
• Allow standing time before serving.
• Use a thermometer to verify safe temperatures.
• Don’t rely on visual cues alone—steam and bubbling don’t guarantee safety.
• Clean regularly to prevent food buildup and odors.

Source:https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/cooking-microwave-ovens