Can Glass Pyrex Go in the Microwave? A Comprehensive Guide
The short answer: Yes, original glass Pyrex is generally considered microwave-safe, but it’s crucial to follow specific usage guidelines to avoid thermal shock and potential breakage. However, modern Pyrex and other similar glass products require extra caution.
The Legacy of Pyrex: From Lab to Kitchen
Pyrex has been a kitchen staple for over a century, known for its perceived durability and resistance to heat. Originally manufactured from borosilicate glass, it could withstand significant temperature changes, making it ideal for both baking and microwaving. However, the manufacturing process changed, impacting the heat resistance of newer products. Understanding this shift is key to answering the question: Can Glass Pyrex Go in the Microwave?
The Composition Conundrum: Borosilicate vs. Soda-Lime Glass
The pivotal change occurred when Corning, the original manufacturer of Pyrex, sold the brand’s rights to different companies in different regions. While European Pyrex often remains borosilicate, Pyrex manufactured in the United States predominantly uses soda-lime glass.
- Borosilicate glass: This type of glass is more resistant to thermal shock due to its lower coefficient of thermal expansion. This means it can better handle sudden temperature changes without cracking or shattering.
- Soda-lime glass: This is a cheaper and more readily available glass type, but it is more susceptible to thermal shock.
The switch to soda-lime glass means that modern Pyrex is not as heat-resistant as its older counterpart.
Understanding Thermal Shock: The Enemy of Glassware
Thermal shock occurs when different parts of a glass object heat or cool at different rates, causing internal stresses that can lead to cracking or shattering. This is a primary concern when microwaving glass containers. Factors that contribute to thermal shock include:
- Rapid temperature changes: Sudden transitions from cold to hot or vice versa.
- Uneven heating: Microwaves don’t always heat food uniformly, creating hot spots in the container.
- Pre-existing flaws: Scratches or chips in the glass can weaken its structure and make it more prone to breakage.
- Empty Microwaving: Never microwave empty Pyrex. The glass could overheat and shatter due to lack of moisture.
Safe Microwaving Practices with Glass Pyrex
Even though original glass Pyrex is relatively microwave-safe, it’s important to take precautions to minimize the risk of thermal shock. Here are some best practices:
- Avoid extreme temperature changes: Let refrigerated food warm slightly before microwaving. Never place a cold Pyrex dish directly into a hot microwave.
- Use low power settings: Microwaving on lower power levels allows for more even heating.
- Stir or rotate food frequently: This helps distribute heat and prevent hot spots.
- Never microwave empty Pyrex: Always ensure the dish contains food or liquid.
- Avoid microwaving Pyrex with metal trim: Metal can cause arcing and damage the microwave or the dish.
- Inspect for damage: Check your Pyrex dishes for any cracks, chips, or scratches before use. Discard any damaged dishes.
Visual Inspection: Identifying Your Pyrex
Determining if you have older borosilicate or newer soda-lime glass Pyrex can be tricky. While labels aren’t always definitive, here are some clues:
- Country of Origin: Older Pyrex is often marked “Made in USA”. Modern Pyrex may be made in France or other countries. This is not a foolproof indicator, though.
- Weight: Borosilicate glass is generally lighter than soda-lime glass for the same size dish.
- Tap Test: Some people claim a borosilicate dish will produce a clearer, more resonant ring when tapped than a soda-lime dish, but this is subjective.
- Manufacturer’s Website: Checking the manufacturer’s website (currently Instant Brands for US Pyrex) might provide information based on the product code or markings on your dish.
| Feature | Borosilicate Glass (Older Pyrex) | Soda-Lime Glass (Modern Pyrex) |
|---|---|---|
| Heat Resistance | Higher | Lower |
| Thermal Shock Resistance | Higher | Lower |
| Weight | Lighter | Heavier |
| Common Origin | USA | USA/France/China |
Best Practices: General Microwaving Safety
Regardless of the type of glassware you use, follow these general microwaving safety tips:
- Always use microwave-safe containers.
- Never microwave food in metal containers or with metal utensils.
- Do not seal containers tightly, as steam buildup can cause explosions.
- Follow the manufacturer’s instructions for microwaving food and containers.
- Use oven mitts or pot holders when removing hot dishes from the microwave.
Frequently Asked Questions (FAQs)
Is it safe to microwave Pyrex straight from the refrigerator?
It’s not recommended to put Pyrex directly from the refrigerator into the microwave. The sudden temperature change increases the risk of thermal shock and potential breakage. Let the dish sit at room temperature for a few minutes before microwaving.
Can I microwave Pyrex that has a small crack or chip?
Absolutely not. Even a small crack or chip can weaken the glass and make it much more likely to shatter in the microwave. Discard any Pyrex with damage.
What happens if Pyrex shatters in the microwave?
If Pyrex shatters in the microwave, immediately turn off the appliance and unplug it. Avoid touching the broken glass until it has cooled completely. Carefully sweep up the glass fragments, wearing gloves and eye protection.
Is it okay to microwave Pyrex with a plastic lid?
Only microwave Pyrex with a plastic lid if the lid is specifically labeled as microwave-safe. Otherwise, the lid may melt or warp. It’s better to use microwave-safe plastic wrap or a paper towel to cover the dish. Always vent the covering to allow steam to escape.
Can I use Pyrex in a convection microwave oven?
Yes, you can generally use glass Pyrex in a convection microwave oven, but make sure it’s heat-safe and oven-safe. Always consult the manufacturer’s instructions for both the Pyrex dish and the convection microwave oven.
Does all Pyrex have the same heat resistance?
No. As discussed, older glass Pyrex made of borosilicate glass has higher heat resistance compared to newer Pyrex made of soda-lime glass.
How can I tell if my Pyrex is microwave-safe?
Look for a microwave-safe symbol on the dish. This symbol usually depicts a microwave oven with a dish inside. If you are unsure, err on the side of caution and use a different container.
Can I bake with Pyrex then immediately microwave the leftovers in the same dish?
While technically you can, allowing the Pyrex to cool down significantly between baking and microwaving will reduce the risk of thermal shock.
What is the best power setting to use when microwaving Pyrex?
Using a lower power setting (e.g., medium or low) allows for more even heating and reduces the risk of thermal shock.
Is it better to microwave food covered or uncovered in Pyrex?
It depends on the food. Covering the food helps to retain moisture, but it can also create steam buildup. Vent the covering or leave a small gap to allow steam to escape. Follow recipe instructions.
Can I put ice water in a hot Pyrex dish after microwaving?
Never do this. This is a guaranteed recipe for thermal shock and shattering. Always let the Pyrex cool down gradually.
Where can I find more information about the safety of microwaving Pyrex?
Check the manufacturer’s website (Instant Brands for US Pyrex), consult reputable cooking websites, and read user reviews for experiences with microwaving Pyrex.