Can You Microwave Glass? (4 Risks Revealed)

Given how busy life has gotten these days, a lot of people skip cooking every day and usually prefer heating up last night’s leftovers or getting takeout. 

In times like these, when we heavily rely on our microwaves to heat up our food for us, it’s important to know about microwave safety. Especially since most of us store and freeze our food in glass containers.

So can you microwave glass? Is it safe to do so? Can you microwave all kinds of glass? Here’s everything you need to know.

Can you microwave glass?

Generally, you can microwave most glassware that has a microwave-safe label. However, you should not microwave some glass materials like glassware with metallic trims, colored glassware, and glass ceramics unless it is labeled otherwise. 

To determine whether you can microwave the kind of glass you have, check the bottom. If it has a microwave-safe symbol (a microwave with three squiggly lines inside it), it is safe to microwave.

If there’s no symbol or label, you can do a quick test. Fill the glass with water and nuke it for a minute on high heat. If the water heats up but the dish remains cool to the touch, you can microwave it. But if the water stays cold and the glass heats up, then you should not put that dish in the microwave. 

Microwaving unsafe glass can explode in the microwave. Generally, decorative glass should not be microwaved, but it is safe to microwave glass without gold or silver rims.  

Is all glass safe to microwave?

Unfortunately, not all glass is microwave-safe. It is possible to use some of them to cook or reheat food but some glass containers can break when they’re subjected to extreme temperatures.

We’ve all been there; wondering whether or not it’s safe to microwave that glass jar, bottle, or dish. 

Pyrex is usually microwave-safe since it is stable and has high heat resistance. In fact, it can even handle heat up to 1000 degrees Celsius! It is also durable and acid-resistant.  

Meanwhile, it’s not very safe to microwave ordinary or toughened glass containers for a longer duration. At most, you should just microwave them for up to 3 minutes. Any longer than that, and the glass might just explode.

Similarly, the delicate glass will most likely crack when it’s exposed to high heat. Curved and crystal glass products can also burst if you use them to heat oily food, especially because these products have uneven thickness.

In particular, you should stick to Pyrex or some other similar microwave-safe glassware when heating foods rich in sugar and fat. This is because these foods heat up at a higher temperature compared to water-based foods. So make sure you’re very cautious when microwaving such food. 

What kinds of glass are not microwave-safe? 

Colored glass and glass with metal trimming are not safe to use in the microwave. But Pyrex is considered microwave-safe. 

Glass colored with dyes or other chemicals is not microwave-safe. When subjected to heat, chemicals in the glass can leach into your food and contaminate it. This won’t break the glass, but it can lead to serious diseases like cancer. In some cases, some dyes add air bubbles to the glass, eventually causing it to expand, crack, and break.

Similarly, glass cups or plates with metal trims should not be put in the microwave. This is because the metal can spark. Depending on the kind of food or drink inside the metal-trimmed glass, it can even result in fire.    

On the other hand, Pyrex is microwave-safe. It is made using soda-lime glass that can handle prolonged exposure to extreme heat and tolerate quick changes in the temperature.

Can glass break in the microwave?

Yes, some kinds of glass can break in the microwave. This is because some types have tiny air bubbles inside them that tend to expand when they’re heated. As the heat increases and the bubbles heat up, they cause the glass to stretch and eventually break. 

Heating the glass can also lead to thermal stress. This is when one part of the glass gets hotter than the other parts. If the stress is high enough, it can even break the glass.

Similarly, embellishments and decorations affect the glassware’s structural integrity. Some glass dishes and containers are even trimmed with metal so they can’t be put in the microwave. If you do microwave them, the metal will spark and shatter the glass.

Even a microwave-safe glass can break in the microwave if it is chipped or has tiny cracks. Your glassware can also break because of uneven heating. 

Make sure you thoroughly check the glassware before nuking it in the microwave. Make sure you don’t microwave glass with gold or silver rims as they may spark when subjected to electromagnetic waves. 

Can glass melt in the microwave?

It is impossible for glass to melt in the microwave. The appliance is unable to produce the heat needed to melt it. 

Glass melts at a temperature between 900 and 1600 degrees Fahrenheit. But it is impossible for microwave ovens to produce that amount of heat. So even if you microwave the glass for hours, it won’t melt. 

Glass can easily handle extreme temperatures so it won’t break if it is subjected to very hot or very cold temperatures. However, rapidly changing the temperature of the glass increases the chances of it breaking.

Should you microwave cold glass?

You should not immediately microwave cold or frozen glass. Let it thaw first and wipe the condensation from it before putting it in the microwave.

If you’re planning on putting frozen food with the cold glass container in the microwave, there are two things you should do. 

First, let the frozen food thaw to room temperature and then transfer it to the microwave. Second, when you take the container out of the freezer, you’ll see condensation on its surface. Make sure you remove it before microwaving the container.  

And of course, when you’re done microwaving, be careful while handling the hot dish. Use kitchen gloves or pot holders so that you don’t burn yourself or drop the hot dish.

If you can’t wait for the glass container to thaw and come down to room temperature, then you should heat it slowly. Nuke it at the lowest power first before gradually increasing it until you get to the desired temperature. 

Tips for microwaving glass

Some other things you should keep in mind when microwaving glass are:

  • Glassware that has a microwave-safe label is your best bet for cooking or reheating food in the microwave. And even though some glass containers don’t have the label, they are still safe to use since they don’t leach toxins into your food like plastic. The absence of the safety label just means that the glass is delicate and of poor quality but it doesn’t mean that it will explode. However, it might crack if a quick thermodynamic transition takes place. 
  • Metal sparks can destroy poor-quality and fragile glass. The glass won’t catch fire, but it can crack or shatter because of the quick energy surge. 
  • You shouldn’t microwave cheap glass since it is usually not heat-resistant and can shatter when subjected to high temperatures.  
  • Avoid heating cold glass with frozen things in the microwave. If you absolutely have to, make sure you do it on low heat and continuously stir the food to ensure heat spreads throughout the container or dish.  

The Bottom Line

You now know whether you can microwave glass or not. The important thing is to check for the microwave-safe label or symbol. And if you don’t find any of these, you can go ahead and do a quick water test. 

Remember to never microwave poor-quality, colored, or metal-trimmed glass since they will most likely break. Instead, try to stick to materials that you know are microwave-safe like Pyrex. 

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