Buzz
Do you need to boil water for a beverage or a dish? A microwave is a handy tool for heating small amounts of water without needing a stove or electric kettle. However, boiling water in a microwave comes with its own challenges. For instance, though rare, there is a risk of water overheating, suddenly erupting, and potentially causing burns. While the risk is low, it’s wise to take precautions to ensure safety when heating water.
- Preparation Time: 1 minute
- Cooking Time: 1-3 minutes
- Total Time: 2-4 minutes
Steps
Choose a Microwave-Safe Container
Bước đầu tiên để đun nước an toàn trong lò vi sóng là dùng vật đựng thích hợp. Bảng thông tin rõ ràng sau đây sẽ giúp bạn xác định vật đựng thích hợp cho việc này.
| Vật liệu | Có an toàn hay không? | Ghi chú |
|---|---|---|
| Thủy tinh | Có | |
| Gốm sứ | Có | |
| Đĩa giấy | Có | |
| Giấy nến/giấy sáp | Có | |
| Hầu hết kim loại (bao gồm giấy bạc và bộ đồ ăn bằng bạc) | Không | Kim loại đun trong lò vi sóng sẽ bắn tia lửa có thể làm hỏng lò vi sóng, thậm chí gây cháy. |
| Túi giấy nâu | Không | Có thể phát cháy hoặc giải phóng các khí độc trong lò vi sóng. |
| Vật bọc kín/đậy kín | Không | Có thể nổ do hơi nước nóng. |
| Các vật đựng có thiết kế dùng một lần (cốc sữa chua, cốc bơ thực vật, v.v…) | Không | Có thể chảy, cháy hoặc tỏa khí độc. |
| Nhựa (màng bọc thực phẩm, hộp đựng thực phẩm Tupperware-esque v.v...) | Thường là không | Các hóa chất độc hại trong nhựa có thể ngấm vào thức ăn. Tuy nhiên, các vật đựng bằng nhựa có đóng dấu chứng thực của FDA "microwave safe" (an toàn trong lò vi sóng) có thể dùng được. |
| Hộp xốp | Thường là không | Xem phần chất liệu nhựa; một số hộp xốp được đóng dấu "microwave safe" có thể dùng được. |
Safely Boil Water
Pour water into a microwave-safe cup or bowl. Boiling water in a microwave is straightforward. Start by pouring water into a container made of materials safe for microwave use, as listed in the table above.
- Remember not to seal the container tightly. Hot steam can cause it to explode.
Place a clean, microwave-safe object into the water. After pouring water into the cup, place a non-metallic object like a wooden spoon, chopstick, or popsicle stick into the water. This helps prevent the dangerous phenomenon called "superheating" by providing nucleation points for bubbles to form.
- Superheating occurs when water in a microwave heats beyond its boiling point without bubbling due to the lack of nucleation sites (rough spots needed for bubbles to form). When disturbed or introduced to a nucleation site, superheated water rapidly produces steam, causing a small explosion in the boiling water.
- If no suitable object is available, you can use a scratched or chipped container. These imperfections act as nucleation sites to help bubbles form.
Place the water in the microwave. Heat the water in short intervals (no more than 1.5 minutes at a time), stirring occasionally until steam rises. Even with the precautions above, bubbles may not form as visibly as when boiling water on a stove. The most accurate way to check if the water is boiling is by using a thermometer. At sea level, water boils at 100°C. This temperature decreases at higher altitudes.
- If using a heat-retaining container (like glass or ceramic), be cautious when removing it to stir. Use a towel or oven mitt to prevent burns.
To sterilize water, continue boiling. If you want purified water, heat it in the microwave long enough to kill microorganisms. The U.S. Centers for Disease Control and Prevention recommends boiling water for at least 1 minute or 3 minutes if you are above 2,000 meters in elevation.
Avoiding the Hazards of Superheating (Additional Tips)
Avoid heating water for too long in one go. After reading the tips above, you might worry about accidents caused by superheated water. Don’t fret! There are several ways to stay safe. Perhaps the most important step to avoid superheating is not to heat water for extended periods at once. Water won’t superheat if it doesn’t exceed its boiling point.
- The exact time limit for each heating interval may vary depending on your microwave’s power. To be safe, start with a 1-minute limit for the first interval. Based on the water’s temperature after the first round, adjust subsequent intervals accordingly.
Avoid using overly smooth containers. For the same reason you should add a non-metallic object or use a scratched container, avoid using overly smooth containers like new glass cups or ceramic bowls; many materials can be too smooth and cause issues.
- Instead, opt for older, worn containers or those with visible scratches at the bottom; these imperfections act as nucleation sites for bubbles to form.
Carefully tap the side of the container after heating. When you think the water has been heated enough, check if it’s superheated by tapping the side of the container before removing it from the microwave. It’s best to use a long utensil to protect your hands.
- If the water is truly superheated, tapping the container may cause it to suddenly "explode" on the surface. This can cause water to spill inside the microwave, but you’ll avoid burns since you haven’t removed it yet.
Use a long utensil to stir the water while it’s still in the microwave. Still unsure if the water is superheated? Use a long stick to stir it gently. Stirring or adding an object creates nucleation sites for bubbles to form; if the water is superheated, it will quickly "explode" or boil over. If not, congratulations! The water has been safely boiled.
Keep heated water away from your face until you’re sure it’s safe. It almost goes without saying, but you should never bring your face close to water that might be superheated, even slightly. Most injuries from superheated water occur when people remove it from the microwave and look inside; the sudden eruption of superheated water can cause severe facial burns and, in the worst cases, permanent vision damage.
Warnings
- A cup of water with nothing inside (such as a chopstick) has a higher risk of superheating because bubbles have no place to form. Adding an object to the water is a small but crucial step.
- Do not microwave water in a sealed container. Expanding steam can cause the container to burst, creating a huge mess!
