You can use glass food containers with your microwave, sure. They’re almost always deemed as microwave safe versus most Styrofoam or plastic containers, which require a label indicating such, and even then, they can only be used for so long. However, like with plastic and Styrofoam, not all glass is microwave safe and some glass isn’t thick enough to take the sudden high temperatures you can achieve from microwave usage.
Further reading: Can You Microwave Styrofoam?
You also need to err on the side of caution and check if the glassware is labeled microwave safe. Here are some helpful tips and tricks in dealing with the question: Can you microwave glass?
So Can You Microwave Glass?
Yes and no. Yes, many glassware containers can be microwaved but some can’t. Some glassware can shatter if heated up too high due to its thickness. It’s best to stick to products labeled “microwave safe”, to be honest. However, unlike Styro and plastic, there is more no-label glassware you can use for reheating purposes on a microwave oven.
- Testing Out Glassware: There’s a safe way to check if the glassware is microwaveable or not even if they lack a label. You can do so even without risking cracking or shattering the glassware. Just microwave them for a minute or two. If your drinking glass or glass baked macaroni container is hot after only a minute then it’s not microwave-safe. If it is slightly cool afterwards then it is totally microwave-safe.
- Glass Concerns with Microwave Usage: Glass that isn’t microwave-safe might have air bubbles so tiny it’s not visible to the naked eye. if these bubbles inside your glassware were to expand enough from rising temperatures then this can result in shattered glass or at least the container getting a hairline crack that totally doesn’t bode well to future microwaving. For the most part, glassware made for conventional ovens tend to be microwave-safe as well.
- Metal on Glass and Colored Glassware: If your glassware has metal handles on it, it could spark and cause your container to break into a million pieces as well. Colored glass containers should have a “microwave-safe” or “microwave safe” label on it. The dyes used to make the glass colored might not be safe for food. The labels are there to make sure that you know the colored glass container won’t contaminate your food if it’s heated up.
- Using Ceramic vs. Glass: Ceramic plates, bowls and containers are microwave-safe because they’re fried and baked clay. Ceramic are likelier to be microwave-safe even if they’re not labeled as such. With glassware, it’s safer than Styrofoam and plastic but you still want to make absolutely sure it won’t literally crack from the pressure of constant reheating from your microwave oven. There are dangers you should watch out for.
- Microwave Must Nots: Glassware that’s heated in the microwave then cooled too quickly might crack or shatter. Many of them, especially the tinted ones, will have a label telling you whether they’re microwave-safe or not. If the glass contains any metal don’t use it with a microwave. Ditto when it comes to foil and metallic takeout containers. Other microwave-unsafe containers include foam-insulated cups, dairy storage containers, and brown paper bags. You should put them in ceramic containers instead.
- Labels on Plastic and Glassware: Even though some plastics are labeled microwave-safe, you shouldn’t overuse them. Many of them are one-time use only. Otherwise, if they’re cracked and torn don’t use them with your microwave oven. Ditto when it comes to any cracked glassware. If you’re using glassware that has hairline cracks because they’re still serviceable, you shouldn’t use them for reheating with a microwave oven or even a regular oven. As much as possible, check the label for any “microwave-safe” reassurance to play things safe.
How to Tell if Something is Microwave-Safe
Are you not sure that your glassware is microwave-safe? Here’s a more in-depth look into how to ensure that your bowl and plates made of glass instead of ceramic can be used safely with your microwave oven. This is especially useful if there’s no indicator or label at the bottom of the dish or plate signifying its safeness for microwave use.
- Examine the Dish: Turn the dish over and look for labels on the bottom declaring if it’s microwave-safe. Many glass containers and dishes state either “Not for Use in Microwaves” or “Microwave Safe”. If there’s no label available, you can test the dish yourself with the microwave in a safe manner.
- Turn Up the Heat: Get the highest power setting for your microwave. Turning up the heat of your microwave varies from model to model or manufacturer to manufacturer. Consult the user manual of your specific make and model of microwave oven to get the proper instructions for it. Most microwaves have a “Settings”, “Menu”, “Power Level”, or “Power” button that allows you to get the highest power setting. Thankfully, the default setting is usually the highest power setting and other modes such as “Defrost” have their own power settings.
- Add Water: Fill a glass bowl or measuring cup with a cup of water. Place it on the dish in question that you intend to heat up with your microwave. If you have a bigger container or dish, you can place the cup inside or on the dish. Don’t use the dish as your water bowl for the sake of this “microwave safeness” test. The cup of water is the key to this experiment. You should heat the cup up without heating up the container to ensure container safeness.
- Set the Time and Check the Heat: Finally, microwave the glassware dish and the microwave-safe cup for a minute. If the container or dish is warm or hot after the process, it’s not microwave-safe. If the container or dish itself is cool or normal temperature while it’s the cup of water that’s hot then the dish is microwave-safe. If you placed the cup in or on the dish, the area around the cup might be warm but if the rest of the container is cool then it’s microwave-safe.
As much as possible, look for the magic words, “microwave-safe” or “microwave safe” on any containers made of glass, ceramic, plastic, or Styrofoam before using them with your microwave. With ceramic, it’s less so a concern because usually they’re safe by default as well as many particularly thick pieces of glassware.
- Is Glassware Microwave-Safe? Yes, it’s almost always microwave-safe. Even without a label you’re usually guaranteed of something that won’t easily break or catch fire if heated. However, if it’s thin glass or has cracks on it you should err on the side of caution. It might have a heat or temperature limit. You should also let it gradually cool down after being microwaved because if it cools down too quickly it might break. There are thankfully ways to check if your piece of new glassware is microwave-safe even if it’s not marked as such.
- Is Ceramic Microwave-Safe? Yes, most ceramics if not all of them are safe for use with your microwave. You don’t usually even have to check your china set if they have “microwave-safe” labeling on them. Anything made of porcelain and stoneware are usually safe for use with your microwave. However, to err on the side of caution, don’t microwave with cracked ceramics or else you might risk making the damage worse. Additionally, don’t microwave with any ceramic containers that have metallic finishes or edges either.
- Is Plastic Microwave-Safe? Ostensibly, plastic labeled “microwave-safe” are safe for microwave use. If it doesn’t have the label, don’t use it with your microwave. Avoid disposable or single-use plastic containers because those might contaminate your food as it’s microwaved, if not outright meltdown altogether. It’s rare, but if your plastic has metal or foil included into it then don’t use it with your microwave either since the metal can cause sparks or catch fire inside your microwave as well.
- Is Styrofoam Microwave-Safe? Some Styrofoam containers are labeled as microwave-safe. Don’t microwave single-use containers from restaurants and the like. Some microwave-safe Styro can only be microwaved once as well. Don’t microwave a damaged Styro container either, even if it’s labeled as microwave-safe. The safest Styrofoam container to microwave is one that’s undamaged, haven’t been microwaved before or multiple times, and has the label that marks it as microwave-safe.
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Nowadays, convenience is the priority and leftover foodstuffs are abundant. Therefore, knowing about microwave usage and safety is the key to surviving in today’s world without going back to our food-wasting past.
You’d think they’d be as safe as ceramic plates but that isn’t the case. Some of them have tiny air bubbles inside of them that could burst if heated for too much, too hot, or too long. If there isn’t a “microwave-safe” label on your glassware, err on the side of caution for glassware that’s thin and don’t use it on the microwave. As for thicker glassware, safely check if it’s microwaveable with the 1-minute heating test. If after heating the glassware it’s hot to the touch instead of cool in some parts then it’s not microwave-safe.
- Andrea Boldt, “Is it Safe to Put Glass in the Microwave?“, Leaf.tv, Retrieved December 25, 2020
- “Guide: How to Tell if Something is Microwave Safe“, Overstock.com, November 18, 2015