Choosing the right container for microwave cooking is about more than convenience. The wrong container can warp, melt, leach harmful chemicals into your food, or cause dangerous situations like fires or burns. This comprehensive guide explains which materials are safe, how to identify microwave-safe products, and what to avoid.
Understanding Microwave-Safe Symbols
The most reliable way to determine if a container is microwave-safe is to look for the microwave-safe symbol: typically three wavy lines stacked above each other, sometimes inside a microwave icon or dish outline. This symbol indicates the manufacturer has tested the product and confirmed it won't melt, warp, or release harmful substances when microwaved.
In Australia, products meeting food contact standards should be clearly labelled. However, the absence of a symbol doesn't necessarily mean a container is unsafe; it may simply indicate the manufacturer hasn't tested or certified it for microwave use. When in doubt, test the container yourself or choose an alternative you're confident about.
Fill the container with water and microwave on high for one minute. If the container remains cool while the water heats, it's likely microwave-safe. If the container becomes hot, it's absorbing microwave energy and shouldn't be used in the microwave.
Safe Materials for Microwave Use
Glass
Most glass containers are naturally microwave-safe. Glass doesn't absorb microwave energy, so it won't heat up independently of the food inside. However, avoid glass with metallic decorations, paint, or trim, as these can cause sparking. Also avoid using glass that has chips, cracks, or is designed for cold use only (some decorative glass items).
Tempered glass, such as Pyrex or Corelle, is particularly well-suited for microwave use. These products are designed to withstand rapid temperature changes without cracking. Standard glass may crack if moved directly from refrigerator to microwave, so allow refrigerated glass containers to reach room temperature first.
Ceramic and Stoneware
Plain ceramic and stoneware dishes are generally microwave-safe. However, ceramics with metallic glazes, gold or silver decorations, or metallic paint can cause sparking and should be avoided. Some handmade or imported ceramics may contain lead in their glazes, which can leach into food when heated. Stick to ceramics specifically marketed for food use from reputable manufacturers.
To test ceramic items, use the water test described above. Some ceramics absorb microwave energy and become extremely hot, potentially causing burns. If a ceramic dish gets hot while empty or with cold food, avoid using it in the microwave.
Microwave-Safe Plastics
Not all plastics are created equal when it comes to microwave safety. Look for the microwave-safe symbol and check the recycling code on the bottom of the container. Generally safer plastics include:
- HDPE (Code 2): High-density polyethylene is generally considered safe for microwave use.
- LDPE (Code 4): Low-density polyethylene is usually safe but may warp at high temperatures.
- PP (Code 5): Polypropylene is the most microwave-safe plastic and is commonly used in microwave-safe containers.
Never microwave containers marked with recycling codes 3 (PVC), 6 (polystyrene/styrofoam), or 7 (other/mixed plastics that may contain BPA). These can release harmful chemicals when heated. Also avoid single-use containers like margarine tubs or takeaway containers not marked microwave-safe.
Paper Products
Plain paper plates, paper towels, and wax paper are generally safe for short microwave use. They work well for covering food to prevent splatters or reheating items briefly. However, avoid paper with printing, as some inks can transfer to food. Never use paper bags unless specifically designed for microwave use, as some contain adhesives or metal components that can cause fires.
Parchment paper is excellent for microwave cooking, particularly for fish or vegetables steamed in packets. It's designed to withstand heat and won't transfer chemicals to food.
🎯 Quick Reference: Safe Materials
- Glass: Most types, avoid metallic decorations
- Ceramic: Plain, food-grade pieces without metallic glazes
- Plastic: Codes 2, 4, 5 with microwave-safe symbol
- Paper: Plain, unprinted plates and towels for short use
- Silicone: Food-grade silicone marked as microwave-safe
Materials to Avoid
Metal
Metal containers, aluminium foil, and utensils should not be used in most microwaves. Metal reflects microwaves, which can cause sparking (arcing), damage the microwave, and potentially start fires. This includes metal twist ties, foil takeaway containers, and dishes with metallic trim or decoration.
Some microwaves are designed to accommodate specific metal accessories, and small amounts of foil can sometimes be used for shielding. Always consult your microwave's manual before using any metal products.
Styrofoam
Standard styrofoam (polystyrene, recycling code 6) should never be microwaved. It can melt, warp, and release potentially harmful chemicals into your food. Some food manufacturers use microwave-safe polystyrene, but unless explicitly marked as microwave-safe, assume styrofoam containers are not suitable for microwave heating.
Certain Plastics
Beyond the recycling codes mentioned earlier, avoid any plastic that has become scratched, stained, or warped from previous use. These signs of degradation indicate the plastic is breaking down and may more readily release chemicals when heated. Old plastic containers, even if originally microwave-safe, should be replaced regularly.
Never microwave plastic wrap directly on food unless it's specifically labelled microwave-safe. When using plastic wrap, leave a corner open for venting and ensure it doesn't touch the food surface.
Special Considerations
Takeaway Containers
Most takeaway containers are not microwave-safe, even if they appear to be sturdy plastic. Chinese food containers with metal handles are obviously unsuitable. Clear plastic clamshell containers, black plastic trays, and foam containers should all be avoided unless marked with the microwave-safe symbol.
Transfer takeaway food to a proper microwave-safe dish before reheating. This takes only a moment and eliminates any risk of container problems.
Food Storage Containers
High-quality food storage systems like Sistema, Décor, and Lock & Lock typically offer microwave-safe options clearly labelled as such. When purchasing food storage containers, look for those specifically designed for microwave use if you plan to reheat food in them.
Note that "microwave-safe" lids may still need to be vented or removed during heating. Check product instructions for specific guidance on lid use during microwaving.
Cookware for Microwave Cooking
Dedicated microwave cookware is designed for specific cooking tasks. Microwave-safe steamers, bacon cookers, rice cookers, and egg poachers can expand your microwave's capabilities. When choosing these products, select items from reputable brands with clear microwave-safe labelling and usage instructions.
Health Considerations
The primary health concern with microwaving containers is chemical leaching. When certain plastics are heated, particularly those containing BPA (bisphenol A) or phthalates, these chemicals can migrate into food. This is particularly true for fatty or oily foods, which absorb these compounds more readily.
Australia banned BPA in baby bottles in 2010, but it remains present in some other plastic products. To minimise exposure, use glass or ceramic containers when possible, especially for fatty foods. When using plastic, ensure it's marked microwave-safe and relatively new.
Choose containers free from BPA and phthalates when possible. Many manufacturers now specifically label their products as free from these compounds. When in doubt, glass and ceramic remain the safest options for microwave cooking.
By understanding which containers are safe and why, you can confidently use your microwave without worrying about safety or health concerns. When uncertain about any container, the safest approach is to transfer food to a dish you know is microwave-safe.