Quick Answer: No, Mason jars are not meant to be put in the microwave. Many people assume that it's perfectly safe to heat Mason jars in the conventional or microwave oven, but there's a very good reason you shouldn't. It's not a design flaw—it's just the way Mason jars are constructed.
Let's dive in to learn more...
What Is a Mason Jar?
In recent years, Mason jars have become hugely popular as coffee mug replacements. They're cheap, able to travel and cool-looking.
The Mason jars was invented in 1858 by John Landis Mason as a canning jar, which is how it's still used today (in addition to its travel mug capacity). It's also used for storage of food, beverages, office supplies or any loose household items.
Mason jars are made of glass, though in your standard Mason jar, it's not tempered glass. This means that it's not capable of withstanding high heat (though it's fine for freezing). In other words, Mason jars are not built to be cooked with, baked with or placed in the oven. It stands to reason, then, that you probably shouldn't microwave them, either.
Using tempered glass for high-heat applications is also crucial for your safety. The process tempered glass undergoes alters the structural tension dynamics so that if it breaks, it'll break into little pieces that are less likely to injure you than big, jagged-edged glass bits.
This doesn't mean you have to worry that Mason jars are ultra fragile, because they're generally pretty sturdy. You just don't want to put them under that kind of heat stress that could cause them to shatter.
For more on microwave cooking, see Our Best Microwave Toaster Oven Combo Picks.
Different Types of Mason Jars
There are many big-name brands in Mason jars, but the most recognizable is probably Ball. You'll see Ball Mason jars at places like Walmart, Target and Home Depot.
Other common brands you might find are Kerr and Bormioli Rocco. If you like, you can contact different manufacturers to find out if any use tempered glass, as it's always possible that you could luck out. However, it's standard practice for companies to use non-tempered glass.
Mason jars do come with different types of screw-top metal lids. You can get a wide-mouth design or a narrower neck. One isn't better than the other— it's all about personal preference.
How Do You Know If a Glass Jar Is Microwave Safe or Not?
In general, the way to tell if a glass jar or other glass item is microwavable is to look for a label on the bottom that says "microwave safe." If you were to find this on a Mason jar, then it would imply that the glass is made to handle high temperatures.
Otherwise, the rule of thumb for glass cookware and thicker glass bowls is to test them out for a minute or two in the microwave (not containing any food or beverages).
In the case of a thin Mason jar, we wouldn't recommend doing the microwave test. You don't want to risk having it shatter inside your microwave.
So unless you see the safety label, it's best not do any kind of microwave cooking or reheating in Mason jars.
Labels on Glass to Be Aware Of
In addition to the "microwave safe" label, you could also see a label that indicates the opposite—that a Mason jar is not microwavable. However, this isn't necessarily something you'll find on most of them.
In fact, it's likely that you won't see any labels on these jars at all. If that's the case, just use them for storage and canning.
Bonus Safety Tips
Love Mason jars? Here are some safety precautions you can take when handling them in extreme temperature situations.
- When canning, don't transfer Mason jars from hot water to a cold or wet counter. Place them on a towel or a heat-proof pad to cool before transferring to the fridge.
- If you want to use a Mason jar as your new coffee or tea thermos, get a cozy for it as the glass will be just about as hot as your beverage.
- Even though they're freezable, Mason jars can get slightly more susceptible to breakage at frigid temperatures. Place some fabric around or between them so that they're protected from clinking against other things in the freezer.