Can You Freeze Pyrex? [Glass Dishes & Tupperware]

Simon Says, “Don’t put the Pyrex directly in the freezer after cooking”. Simon also Says, “If you want to freeze Pyrex, first let the glass container fully cool”. This basic game teaches children how to effectively follow instructions. If you do something that was not specifically directed, you lose the game.

Taking a note from this lesson — while we all understand the general idea of cooking with a glass dish, have you ever actually read the instructions? With recent “claims” of Pyrex dishes exploding in the oven, it has led many people to question what they can and cannot do with this universal glass container. 

Good news Mom! Pyrex is perfectly safe to freeze if you follow the clear-cut instructions provided by the company. Let the meal planning commence! These dishes can handle hot and cold environments. However, they do NOT do well with sudden thermal fluctuations. Thus, follow what Simon Says very closely.

This can ensure that your food is stored safely! In order to do this, let your food fully cool down before storing it in the freezer and completely defrost items before cooking them. It is also imperative that you follow cooking, reheating, and cleaning instructions to guarantee the integrity of the glass. Therefore, you want to avoid direct heat sources, such as a broiler or open flame. 

What Is Pyrex? 

Pyrex is a kitchen and laboratory brand that has been around for over a century. The glassware was originally made of borosilicate glass. However, in recent years, the company sold the license to the brand. This led to the formula changing to the more common, and cheaper, soda-lime glass. 

Pyrex boasts that following this alteration, they began to temper the glass to make it more durable and capable of handling more extreme temperatures. Unfortunately, despite these efforts, the chemical make-up of the material is not quite as capable when it comes to handling drastic temperature fluctuations. 

Thus, we take an inside look at the different types of glass and what this means for the safety component of your bake and storage containers.

Soda-Lime Glass

Soda-lime glass makes up 90% of the glass products used worldwide. It is made with three main ingredients — sand, sodium carbonate, and limestone. It can generally withstand temperatures up to 158 degrees Fahrenheit, but it is susceptible to shock. 

Sand

This is the first ingredient in any type of glass. In case you didn’t know, if you take those beautiful white grains of sand that you find at the beach and heat them up to around 3090 degrees, they will turn into a liquid!

Sodium Carbonate

Sodium Carbonate, otherwise known as soda ash, is a chemical that is added to help reduce the exceptionally high melting temperature of the sand. It also aids in the molding process of the final product. 

Limestone

Limestone is a type of sedimentary rock, made of calcium and magnesium. These compounds are extremely durable. They also help to improve the integrity of the glass.  

Borosilicate Glass

Sand and soda ash are also used to make borosilicate glass. However, instead of limestone, it contains boric oxide and alumina. By adding in other compounds, the glass can take on beneficial attributes, like the ability to withstand cold temperatures when you freeze Pyrex and hot temperatures when you bake it!

Boric Oxide

This chemical comes from the mineral Borax! Yes, this multipurpose cleaner and insecticide is also used to create the glass and ceramic plates that you eat off of and cook food in!

Boric Oxide has the capability of strengthening the material that it is bonded with and it has heat resistant properties. Moreover, by hardening the glass, it also makes it less resistant to scratches and more durable in the long run! 

Alumina

As we all know, glass is quite fragile. In fact, part of the definition of glass is “a hard, brittle substance”. However, when the chemical compound Alumina or Aluminum Oxide is added into the mix, it allows this firm material to become slightly easier to mold. This does not mean that you can stretch it out like putty. Nevertheless, it does give the glass a more flexible quality, almost like metal. 

The Outcome — You Can Bake & Freeze Pyrex Better

The combination of all of these ingredients allows for a product that has increased thermal resistance and improved durability. In other words, you can freeze Pyrex glass containers with no worries! While the company no longer manufactures containers with this chemical makeup, they are still available in Europe and on Amazon! Just make sure to confirm where the dish is made and look for the “Cook & Freeze” line! 

Safety Note — Looking for vintage Pyrex dishes made with this material may seem like a tempting idea. However, cracks and chips will occur over time and with regular use, no matter the type of glass. Thus, it is always best to buy new.

Tempered Glass

Tempered glass is a type of glass that has gone through thermal or chemical treatments to improve the integrity of the material. It is capable of handling constant temperatures of 470 degrees Fahrenheit! It also works well in low temperatures, like when you want to freeze your Pyrex dish. 

What Does All Of This Mean?

Pyrex’s original design works with most temperatures. Conversely, the new material is still capable of handling hot and cold temperatures, but not extreme temperature changes. This is a key detail to take into consideration when you go to freeze your Pyrex. 

Recommendations To Cool and Freeze Pyrex

When you are done with dinner and you are ready to freeze the leftovers in the Pyrex, it is exceptionally important that you allow the Pyrex dish to cool completely before the transfer to a cold fridge or freezer. Additionally, never place a hot Pyrex container on a surface with water on it. Instead, you want it to cool on a dry surface, such as a cooling rack or dry towel.

Moreover, food expands when it freezes. Therefore, allow at minimum three-quarters of an inch of empty space between the food and the lid prior to placing it in the freezer. 

Recommendations To Cook With Pyrex

Furthermore, it is imperative that you follow all usage instructions. This ensures that the container is safe to use and store. Thus, when cooking with Pyrex containers, never use a broiler, put it on a grill or open flame, or directly on the stovetop. These can all lead to rapid temperature changes that can cause cracks or even breakage.

Remember that when reheating frozen meals stored in Pyrex, give them ample time to thaw in the fridge first. It is best to pull out meals the night before you intend to prepare the food. Then, as the oven preheats on the day of serving, allow the dish to sit on the counter before placing it in the oven. This lowers the temperature differential, better ensuring a safe experience.

It is also imperative that you inspect the glass before each use. This can allow you to identify areas of damage before an issue arises while cooking, storing, or reheating food.

Usage Recommendations — Safely Bake And Freeze Pyrex

In order to enjoy a satisfying cooking experience, the makers of Pyrex, have four simple steps that you should always follow. These guidelines ensure the integrity of the products and the safety of Pyrex’s customers. Additionally, the company notes that “If a piece of Pyrex® glassware does become chipped, cracked or deeply scratched, don’t use it”. This will help to prevent the instance of the dish shattering while in use.

Replacement Advice — Chips & Cracks

Despite the fact that the glass is tempered, soda-lime varieties tend to chip and crack easier than other types of glass. This is why it is imperative that inspect the dish upon purchase as well as before each use. The company explicitly states that even if a small fragment breaks away, it can lead to dish shattering. 

How you may ask? Food expands when it freezes. This is exceptionally true for water-based dishes like soup, vegetables, and certain casseroles. Thus, when you freeze your glass Pyrex casserole dish that has a tiny chip in it, this expansion will put pressure on the container. When you pull out the item and place it in the oven, there is a consequent contraction that follows when the dish is defrosted. This will weaken the glass, even more, causing it to break or even “explode”.

It is also important to remember that continuous usage of this item can also lead to breakage. Most Pyrex containers come with a two-year limited warranty. This covers manufacturing problems and heat-related issues (if you follow their usage guidelines). However, the fact that they offer replacement coverage for a small window of time should be a hint. 

Therefore, you should purchase new Pyrex dishes every few years, and as needed. The Pyrex brand is known for being an affordable and dependable option for food storage and preparation, so thankfully replacement will not break the bank! 

Frequently Asked Questions

What causes glass containers to explode?

In 2019, NBC did an investigation that found “850 reports of shattering or exploding glass cookware, including Pyrex and other brands”, over a seven-year span. While uncommon, this can become a reality if the right factors fall into place.

Over time and with frequent use, all glass has the propensity to crack. Furthermore, as detailed above, soda-lime glass is not a material that can handle large temperature changes. Therefore, when a Pyrex dish goes straight from the freezer into the oven, it causes the glass to crack.

It is important to remember that while this so-called “crack” may seem like an explosion, it is not. Manufacturers intend for this scenario to play out! Non-tempered glass breaks in large chunks. This can be quite dangerous for those nearby. In contrast, tempered varieties shatter into small pieces that are prone to cause less of an injury in the “explosion”.

Is it safe to freeze Pyrex containers?

Plastic food storage containers are virtually unbreakable and they are cheap. However, you get what you pay for, and in this instance, you are paying for phthalates, BPA, and other harsh chemicals. 

These will likely not have much of an impact when the Tupperware is cool. However, studies done by Harvard University have shown that heat can cause these chemicals will separate from the plastic and transfer into your food. If you have enough exposure, this can lead to detrimental health impacts. 

Conversely, while using glass containers, there is no worry about this issue. They also are not capable of absorbing smells, food residue or germs, like their plastic counterparts. 

How do you tell the difference between Borosilicate Glass or Soda-Lime Glass?

It is all in the eye of the beholder! Hold your Pyrex up to the light and look at the edge of the dish. Borosilicate glass will remain clear. In contrast, the soda-lime glass will have a blue-green hue to it. 

Other Interesting Guides 

Final Thoughts 

Pyrex is a reputable company. They have been providing families with cookware for generations. Recent years have brought a lot of skepticism with the brand, causing many parents to worry about whether it is safe to use these products with kids running around underfoot.

Take the claims with a grain of salt. All items have the ability to break. The best practices you can use to ensure a safe kitchen and eating environment are to follow the company’s explicit usage and storage instructions. Moreover, replace the dishes every two years and whenever you notice the damage. Before each use, also take the time to inspect your Pyrex containers for cracks and chips.

Finally, and most importantly, NEVER transfer a hot pan to a cool environment (or vice versa). The main takeaway here is that big temperature changes are bad. Let the food cool before you freeze the Pyrex and defrost the food before putting it in the oven. There is a science behind thermal shock. Try not to test it out with your cookware!

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