The microwave: how to reheat evenly, what you can cook and what you mustn't

How a microwave works

Microwave myths

• "Food becomes radioactive" — no. Microwaves are non-ionising radiation, like radio waves. They heat the food and vanish as soon as the oven switches off.
• "Microwaving destroys vitamins" — the opposite. Short times and little water preserve vitamins better than long boiling in a pan, where they leach into the water.
• "Food cooks from the inside out" — no. The outer 1–3 cm heats, and the centre warms from that.
• "Microwaves change proteins in a special way" — no. Heat changes proteins the same way whatever you heat them with.

How to reheat evenly

• Arrange food in a ring around the edge of the plate, leaving the centre empty: the microwave field is weaker in the middle.
• Thick, dense pieces to the outside, thin and soft ones to the centre.
• Cover with a vented microwave lid or a damp paper towel: the steam heats the food evenly and stops it drying out.
• Stir or turn halfway through.
• Use medium power (50–70%) for dense dishes — stews, bakes, meat. The centre has time to heat before the edges dry out.
• Let it stand for 1–2 minutes afterwards: the heat spreads through.

Which containers are safe

• Safe: heatproof glass, ceramic and china without metal rims, plastic marked "microwave safe", silicone, paper towels and baking paper.
• Not safe: metal dishes and foil — they reflect microwaves, can spark and damage the oven.
• Not safe: dishes with gold or silver rims — they spark.
• Not safe: unmarked takeaway containers and bags, polystyrene — they warp when heated, and some substances from the plastic can migrate into food, especially fatty food.
• Not safe: tightly sealed jars and containers — steam pressure can blow the lid off.

What not to do

• Cook eggs in their shells: steam inside bursts the egg, often just as you cut or pick it up. Even a peeled boiled egg can explode — halve it before reheating.
• Heat water for a long time in a smooth mug: it can superheat above 100 °C without bubbling and erupt when you move it or drop in a tea bag. Put a wooden stirrer in the mug and don't overdo the time.
• Heat foods with skins unpierced — sausages, potatoes, tomatoes, yolks: prick them with a fork.
• Run the oven empty — it can damage the magnetron.
• Heat baby food and formula: hot spots form that can scald a baby. If you do, stir thoroughly and test the temperature on your wrist.

Reheating safely

What the microwave does well

• Steamed vegetables: broccoli, green beans, carrots, corn — in a covered bowl with 2 tbsp water, 3–5 minutes on full. They keep their colour and crunch.
• Jacket potatoes: prick with a fork, wrap in a paper towel, 5–8 minutes on full (turn halfway), then stand for 2 minutes.
• Mug eggs: whisk 2 eggs, 2 tbsp milk, salt and cheese in a mug; 1 minute, stir, then 30–45 seconds more.
• Porridge: 50 g oats and 150 ml milk or water in a large bowl, 2 minutes, stir, 30 seconds more.
• Melting chocolate and butter: short 20–30 second bursts, stirring.
• Softening butter for baking: 5–10 seconds, no more.
• Toasting nuts or breadcrumbs: in a thin layer, 1 minute at a time, stirring.

A 2-minute mug cake

Care and cleaning