Can you put Glass in the microwave? (Risks Revealed)

The microwave is such an easy and quick way to get your food cooked or reheated. However, the container used for reheating or cooking your food determines the outcome … a great deal.

Microwave safety begins with getting it right when it comes to the containers your food is placed in for reheating or cooking. Should you get it wrong, you would have either exposed your food to harmful toxins or you would be dealing with a fire hazard.

NEVER assume that all containers are microwave safe. A prime example of that faulty assumption is glassware in the microwave.

While it is common to use glass bowls, and glass dishes in the microwaves, the microwave safety of these glass containers is often overlooked by users.

In this article, we look into the safety of glassware in the microwave? What happens when glassware is used in the microwave? And what sort of glass can be used in the microwave?

Can glass be used in the microwave?

Yes, some glass containers can be used in the microwave. Because glass containers are commonly used to store food or freeze food, it is often assumed that it is ALWAYS microwave-safe but this is not entirely true.

If you are unsure whether the glass container in your hand is fit for microwave use, the best (and safest) thing to do is to turn the container over and check the bottom for a microwave-safe label.

Broken glass on gray background. Black and white photo.

If the microwave-safe label is not on the glass dish, but you really want to know how safe it is for your microwave, you can conduct a mini-test with it in the microwave.

  1. Fill the glass container with some water and place it in the microwave.
  2. Turn microwave heat on high and leave the glass container in for 1 minute.
  3. If the water becomes hot and the glass container remains cold, this means the glassware is high-heat resistant. This means that it is microwave safe.
  4. However, if the water remains cold and the glass container heats up, then abort usage because this means the container is not microwave-safe.
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The danger of using a non-microwave-safe glass container in the microwave is that the glass will crack and break (often explosively) because of the pressure from the heat in the microwave.

Why does glass break in the microwave?

There are a number of reasons why glass breaks in the microwave. One reason is the presence of air bubbles.

The glass that has air bubbles should not be used in the microwave. This is because these air bubbles heat up while the glass is being heated in the microwave. The effect of the air bubbles heating up causes the glass to expand.

And the expansion of the glass is what causes the glass to crack or shatter in the microwave.

Bear in mind that non-microwave-safe glasswares contain air bubbles.

Furthermore, if the glassware to be used has a crack, the glassware can break while in the microwave. That also applies to microwave-safe glassware.

Should a microwave-safe glass bowl or dish have a crack, it is not advisable to use it in a microwave. The reason is that under high temperatures, the crack can lengthen, causing the glassware to break.

Temperature also plays a role when glass breaks in the microwave. Regular glass containers begin to break from 302 degrees Fahrenheit to 392 degrees Fahrenheit (150 degrees Celsius- 200 degrees Celsius).

Another reason why glass breaks in the microwave is ‘arcing.’

What glass is Microwave Safe?

When we see the microwave-safe label at the bottom of a glass container, we can be confident that the container or bowl can be used in the microwave.

But there are other things that let us know when a glass container is safe for microwave use and when it isn’t.

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Glassware that does not have gold or silver trims (metals) can be used in the microwave. When gold or silver is exposed to a heated environment, like the microwave, a process referred to as arcing takes place.

Arcing in a microwave is when sparks break out inside the microwave. The sparks are a result of the clash between the gold, silver, or metallic decorations on the glassware and the heat in the microwave.

Heatproof glassware is safe for microwave use. And iff you are wondering how to determine if the glassware is heatproof, there is the brand, Pyrex.

The Pyrex brand is known for making glass and glassware that is resistant to heat, chemicals, and, even electricity. Manufacturers put the product through rigorous heat tests to ensure its durability and strength.

Pyrex glass is safe in the microwave because it can withstand high temperatures. However, though the Pyrex glass manufacturers have vouched for the microwave safety of their products; their guidelines inform users of the vulnerability of Pyrex glass when exposed to drastic temperature changes.

This sudden change in temperature is referred to as ‘thermal shock’.

If Pyrex glassware is exposed to extreme temperature or comes into direct contact with heat, it will cause the glass to break. Also if a cold Pyrex glass is put into a microwave it will experience thermal shock, which will cause it to break in reaction to the sudden change in temperature.

Do not put cold Pyrex glass in the microwave.

Whether you are baking or cooking, Pyrex glass can withstand temperatures up to 450 degrees Fahrenheit (232 Celsius). Any temperature beyond this will be its breaking point (literally).

If you are baking or cooking anything that requires a higher temperature it is recommended that you use tempered bakeware.

Pyrex comes in a variety of shapes, sizes, and grades. With the Pyrex brand, you are not limited in choice. There is the Pyrex glass cooking pot, bakeware, cooking sheet, dish tray, glass pan, and many others.

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If you are using a Pyrex dish, manufacturers advise that it shouldn’t be used in a dishwasher because that can weaken the strength of the glassware.

How long can you microwave glassware?

Standard glass containers can only be heated in the microwave for 3 minutes. Anything beyond this and the glass will certainly break.

These glass containers begin to break from 302 degrees Fahrenheit to 392 degrees Fahrenheit (150 degrees Celsius- 200 degrees Celsius). A stark difference with Pyrex glass which can withstand temperatures up to 450 degrees Fahrenheit (232 degrees Celsius).

With Pyrex glass and other microwave-safe containers, the length of time depends on the food being cooked or reheated and the manufacturer’s instructions.

Remember, when using a microwave-safe dish it is important to keep an eye on your food. Have regular checks on your food to determine its readiness. This will prevent food from burning, or drying out. It will also ensure glassware is not left in the microwave beyond the time it can withstand

Microwave-safe glassware has its breaking point, so when in use keep to the user guidelines provided by the manufacturer to ensure optimum use and safety.

Things to know when microwaving Glass:

Glassware is a common kitchen utensil in homes. It is used to store food, serve food, and can even be used to cook and reheat food.

But not all glassware is safe for the microwave. The fastest way to confirm if your glassware is microwave-safe or not is by checking the bottom of the container for the microwave-safe label.

However, if there is no microwave-safe label and you want to get to the bottom of the microwave safety of that glassware, you can run a quick 1-minute test with it in the microwave.

Simply put some water in the glass dish and microwave for 1 minute on high heat.

If the water stays cold but the glass container heats up, do not use it in your microwave for cooking or heating food because it is not microwave-safe.

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Should the water heat up but the glassware remains cool, then that is an all-clear on its microwave safety. You can go ahead and use it in your microwave.

Some other things to bear in mind are:

  1. Glasswares with gold, silver, or metallic trims/ decorations are not microwave-safe. These decorative elements react negatively to the heat in the microwave resulting in sparks in the microwave.
  2. Do not use cracked glassware in the microwave, this also applies to microwave-safe glassware. When in contact with heat, the crack can lengthen making it shatter in the microwave.
  3. Pyrex glass is considered to be one of the best glassware dishes to use in the microwave. This is because it is specifically made to be resistant to extreme heat conditions.
  4. Read up on the manufacturer’s instructions and guidelines when using glassware in the microwave.

Wrapping up:

Not all glassware is safe for the microwave. Therefore, ensure you thoroughly verify and confirm its safety before popping it into a microwave.

FAQ

How can I safely heat up a glass cup in the microwave?

To safely heat up a glass cup in the microwave, it’s important to use a glass microwave safe container. Place the cold glass on a room temperature surface and then put it into the microwave. Heat it at slightly warm temperatures for short intervals of time, avoiding using the highest power setting.

Why do some glass dishes shatter when heated in the microwave?

Some glass dishes may shatter when heated in the microwave due to tiny air bubbles that are present within most glass dishes. These bubbles expand rapidly when exposed to high temperatures, causing cracks or even breakage of both the cup and dish.

Can I put any type of glass measuring cup in the microwave?

Not all types of glasses are suitable for heating up in microwaves. It is recommended to use only those measuring cups that are labeled as “microwave-safe” or made from tempered or borosilicate glasses which can withstand sudden changes in temperature without breaking.

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Is it safe to put cold glasses directly into a hot oven or vice versa?

No, putting cold glasses directly into an oven preheated at high temperatures can cause them to crack due to thermal shock caused by rapid expansion and contraction of materials with different coefficients of thermal expansion.

What should I do if my microwaved cold glass becomes too hot after heating?

If your microwaved cold glass becomes too hot after heating, remove it immediately from inside and place it on top of a room-temperature surface like wood or cloth instead of metal surfaces which could further increase its temperature through conduction.

What is the difference between tempered glass and ordinary glass when it comes to microwaving?

Tempered glass is microwave safe, while ordinary glass may shatter due to thermal shock caused by microwaving.

Can I microwave all types of glass cookware?

No, not all glass cookware is safe for microwaving. Only use borosilicate or tempered glass that has a microwave-safe symbol on it.

Is it safe to put foil-lined containers in the microwave?

No, foil-lined containers should never be used in the microwave as they can cause sparks and fires.

What happens if I use the wrong dish or container in the microwave?

Using non-microwave safe containers can lead to explosions, fires, and damage to your appliance.

How do I know if a dish or container is safe for microwaving?

Look for a microwave-safe symbol on the dish or container. If there isn’t one, make sure it’s made from borosilicate or tempered glass – these are both considered microwave-safe materials.

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