Can You Heat Food in a Mason Jar?

If you’re like most people, you’ve got plenty of glassware lying around the house. You may have purchased some of it, while others could be old relics that you’re thinking of reusing in food prep or storage. The question is: can you heat food in a mason jar?

You can heat food in a mason jar if it has a microwave-safe label. However, the glass used in most mason jars is not heat resistant and may react unexpectedly to rapid changes in temperature. Because of this, it’s best to avoid using them in cooking or heating food.

I’ll go into further detail about using mason jars in the rest of this article. I’ll also give more information on the safe use of glassware in cooking.

Knowing When To Use a Mason Jar for Cooking

If you’re planning on using or repurposing a mason jar, good for you! They’re an excellent container for preservatives, sauces, and other goodies.

The problem in using them for cooking is that they’re not all made of the same material.

As I’ll discuss further, different types of glass are for different purposes, and the glass in mason jars is often for storage only.

With that said, you can use many of the jars out there for cooking. However, it would be best to make sure that there’s a microwave-safe label.

It may look different depending on where you are, but often it takes the shape of several squiggly lines over a plate.

Different Types of Glass Respond Differently To Heat

Over the years, different jar production methods have been invented, yielding many types of glass with strengths and weaknesses.

Below are a few types of glass that are common today and their unique characteristics.

Normal Glass

This is your every day, untreated glass.

When making normal glass, the craftsman heats sand, soda ash, and limestone until they can all combine into the same liquid. That liquid is then shaped and cooled.

The benefits of everyday glass are that it’s cheap and isn’t very prone to sudden breakage when appropriately handled.

Tempered Glass

You’ve probably heard of this type of glass. It’s in everything from window panes to scuba gear. It’s also famously used in Pyrex kitchenware.

A unique heating process called tempering goes into making this glass. Once finished, it’s around four times stronger than regular glass.

Using tempered glass is common because the process that goes into making it ensures that it breaks relatively safely if it breaks at all.

However, its strength also happens to be its weakness, as it can be prone to sudden breakage if mishandled or exposed to sudden changes in heat.

Heat Resistant Glass

This is the type of glass you should use to guarantee safe food heating. The more scientific name for it is borosilicate glass.

5% of the mixture in this type of glass is boric oxide. When added to the standard components in glass, it gives it a heat-resistant property.

The benefit of this type of glass is that it’s much more robust when facing drastic temperature changes. The main drawback is that it’s more costly to produce and purchase.

Mason Jar Glass Can Be Heat-Treated

Let’s get back to those glass jars littering your shelves.

Mason jars come in all shapes and sizes, and the type of glass used varies just as much.

Mason Jars Are Made With Various Materials

John Landis Mason patented the glassware using his name in 1858. Up until that point, you would typically seal a jar with wax, so adding a lid that could be screwed on and off made things much more convenient.

The jars became so popular over the years that the term can be used to describe any rubber-sealed or screw-top jar. At first, the jars were made of regular glass, but today, various materials are used.

However, as the production of mason jars is common everywhere, it’s sometimes difficult to know whether the glass is heat-treated or not.

This is why it’s essential to make sure the one you’re planning on using has a microwave-safe label.

Understanding How Heat Interacts With Glass

It’s no secret that after cooling, glass becomes quite fragile. Drop it from a height, and you’re sure to cringe as you wait for it to break.

But glass doesn’t only break from impact. It can also break based on changes in temperature.

Thermal Expansion Coefficient Factors Into Glass Breakage

The thermal expansion coefficient is a scientific term used to describe how quickly something expands when exposed to heat.

Glass has a high thermal expansion coefficient, meaning that it expands quickly when heated. If this expansion hits a certain point, the glass can shatter.

Thermal Stress Contributes to Glass Breakage

Thermal stress is a term that describes when there’s a difference in temperature from one portion of an object to another.

As glass expands quickly, the heating process may leave behind one area of the container that hasn’t been exposed to as much of a temperature change.

The difference between the two temperatures leads to stress which can result in breakage.

Tempered vs. Borosilicate Glass

Both tempered and borosilicate glass can handle rising temperatures more efficiently than regular glass, but they have their limits.

One study found that borosilicate glass may be able to withstand a sudden temperature change of 330°F (165.55°C) compared to 100°F (37.77°C) for tempered glass.

Either way, try your best to avoid sudden dramatic changes in temperature when you’re using a glass jar to heat food.

Using Glass in Cooking

There are many ways that you might try to use a mason jar in cooking, and it’s essential to know how each method can affect the glassware.

Only Microwave Jars if They Are Appropriately Labeled

As mentioned, you should only use glass in the microwave if it’s labeled microwave safe.

This is because the microwave will quickly heat one portion of the glass that’s touching the food while the other portion will lag behind.

This creates thermal stress, leading to breakage in weaker types of glass.

Oven-Heating Is Safer for Glass

As anything put in the oven will take longer to heat than it would in a microwave, this option is generally safer.

However, the use of regular glass should still be avoided if you are using an oven to heat your food.

Some Glasses Are Safe for Stove Cooking

There’s some control over how quickly or slowly you heat food on a stovetop.

The use of tempered or borosilicate glass will likely be acceptable. Still, you should avoid adding ingredients with drastically different temperatures like cold water or milk to a heated piece of glass.

The Most Common Ways To Use Mason Jars

John Landis Mason’s invention was originally meant for the storage and preservation of food.

The tight sealing lids allowed things like pickled foods, jams, and sauces to stay edible for an extended time as it’s nearly impossible for bacteria to enter the container.

However, in recent years, people have found new and exciting ways of using these old jars as temporary vessels for salads, breakfasts, and even drinks.

These methods should all be fine, as long as they’re not used for cooking.