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Jan 11, 2013 08:20 AM

Microwave safe glass getting too hot

I've been making hot tea in microwave safe glass measuring/pour cups for many years. Usually Pyrex brand. I put in about 3 cups of water, a tea bag, and set it for 4 minutes, finish, take it out, then let it sit a while. I got a new 4 cup Anchor brand measuring cup, it says microwave safe on the bottom, it looks very similar to the Pyrex ones. I did the same thing I always do. 4 minutes, watched it the whole time, water never comes to a boil except little bubbles around the bag. I went to pick it up by the handle like I always do, and it absolutely burned my fingers in about a half second, I'm getting blisters. I spilled the tea everywhere on my legs and feet, they are red. The empty container handle stayed too hot to touch by bare hand for more than 15 minutes, and it's been a half hour and it's still pretty hot. The container part was cool when empty, the handle was the only part that remained hot. Now, I was probably stupid for not checking the handle, but like I said, I've been doing the same thing for years, really didn't even think about it, I cook many things in those containers, even running some longer than that, I've never had the handle of anything I've had get that hot, especially the entire handle all the way to the end. The Pyrex ones aren't really even warm after that long. Anyone else run into this? I'm not going to use it anymore when the Pyrex ones stay cool enough to use.

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  1. Some containers that are supposedly microwave safe are actually only safe for what they call "reheating." I had to throw away 2 such containers when I saw that was the fine print on the bottom. I too got severe burn on my finger when I picked one up by the handle---ouch!

    1. Much glass is made with some metal, thus the heat. l still use only Pyrex for this reason. Would also be afraid of the cup exploding in microwave if got scratched and then too hot.

      1. I actually got two identical ones. I did the same test with the second one, and it does not do that at all. A little warm I can use, but I also wonder about it exploding or something. If it gets hot enough to fry an egg, hard to say what it would do. I did some online research and I see some issues with newer glass products, never gave it a thought before. Shame that about everything is getting so cheaply made. I think I should just stop using that hand for anything. I'm getting blisters from that, and I smashed my finger dropping a PTO shaft, so I'm losing another fingernail, after just having another one on the same hand finally grown all the way back. Thanks for the replies.

        1. First, I hope you got medical attention...second degree burns can get infected if not properly treated. I guess the lesson is that "microwave safe" means that it will neither wreck or be wrecked by your microwave when used "normally". Different types have different properties as you have found. Further, brand new glass is relatively free of scratches that encourage water to boil...this can allow water to superheat. (Boiling water tends to moderate temperatures).Disruption of superheated water can cause flash boiling...I suspect that this may have happened to you.
          Sorry for the painful experience...get well soon!

          1 Reply
          1. re: MikeB3542

            As MikeB said, 'microwave safe' means it's safe for the dish, it doesn't necessarily indicate that it's safe for *you*.
            A plate under any new microwavable dish lets you lift it out without endangering your toes. We have a few bowls that get pretty hot despite the indication on the bottom, so I try to remember to put a plate under them before I put them in the microwave.

          2. Sounds like you experienced the phenomenon of super-heating. You can google this to find out more. Essentially, it happens when a substance heats up beyond the boiling point without actually boiling.

            There is some dispute about whether this only happens in clear glass containers, as opposed to an opaque ceramic container. There is also dispute about whether it only happens with tap water that contains impurities or with distilled water. Reports are mixed on the validity of both of these claims.

            Also, "microwave save" does not mean cool to the touch. It just means that the container won't spark, like most metals, or melt, like many plastics, or outright break in a microwave.

            I would be very cautious about using a microwave to heat water hot enough for tea. Get a tea kettle and boil the water there.

            1 Reply
            1. re: taos

              A coworker once heated up some gravy or sauce in a coffee cup in the microwave, and when he put a spoon in the cup to stir it, the sauce exploded everywhere.
              Someone said that had to do with the superheating thing. Interesting to see, but I'm glad it wasn't on *my* desk!