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I used a glass bowl as a double boiler for making scrambled eggs and it broke. I know that rapid cooling and heating caused glass to break. for some reason I thought the thick glass bowl would not break.

so how do I ensure I do not break another glass bowl while double boiling?

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    If you use a metal bowl, you can be sure you won't break a glass bowl. Why would you prefer a glass bowl to a metal one for this?
    – The Photon
    Commented Jan 26, 2019 at 17:50
  • I'm using metal now, but If i ever had to use a glass bowl again I need to make sure I'm not doing the same mistake again.
    – Viv
    Commented Jan 26, 2019 at 22:13
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    @Viv using glass in this circumstance was the mistake, so if you do use a glass bowl again, then you're necessarily making the same mistake again. As mentioned in Stephie's answer, something like Pyrex will give you a better chance, but she overstates her case in that, even for Pyrex, you will still be significantly stressing the bowl to do this with it, so do so only if you need transparency or the like, and need it bad enough to accept that you're harming the service life of the bowl, and still risking some chance of it shattering, even with it being Pyrex.
    – Matthew Najmon
    Commented Jan 27, 2019 at 15:04
  • @Matthew Pyrex or ceramic works really nicely - better than thin metal IME, as it holds a bit more heat (my preferred option is a ceramic pie dish because it fits really well in one of my saucepans). Pyrex (even the tempered stuff sold under that name in some countries) should last forever under those conditions
    – Chris H
    Commented Jan 27, 2019 at 16:01
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    @ChrisH How, exactly, is holding more heat a desirable quality in the inner bowl of a double boiler? Make the wall as thin and conductive as you can (metals are good for this), then when you want it to resist sudden temperature changes, the water on the outside of the inner container has all the heat capacity you could want, while still retaining the option to pull it out of that water when rapid cooling is desired (but not nearly as rapid without shattering your Pyrex as I can get without damaging my metal bowl).
    – Matthew Najmon
    Commented Jan 27, 2019 at 22:22

3 Answers 3

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Thickness is not an indicator of heat-proof glass, just think about laboratory glassware, which is sometimes quite thin. It’s rather the other way round, thermal conductivity is low for glass which can increase inner tension when heated quickly. Thicker glass will be more robust against mechanical force, simply because it’s thicker.

If you want to be sure, get a bowl that is labeled as “heat-proof” or similar (terms may vary). It’s still a good idea to avoid sudden temperature swings, just to be sure although some manufacturers claim that their products can withstand temperature swings of 150K. It shouldn’t be an issue with melting chocolate, because you should place the bowl over (not “in” or “touching”) barely simmering water anyway and not have the water in the lower pot at a full rolling boil. There’s a good chance that even non-ovenproof bowls will stand up to this, but as you experienced, it can go wrong.

Another, often overlooked factor is the tension within the heated glass, especially if the temperature distribution is uneven (again: don’t boil the water at full speed). The glass will be more sensitive to shocks, so don’t bang the bowl with a metal spoon when stirring or getting leftovers off the spoon and don’t set it down hard on the table or counter.

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    You drastically overstate your case. If she has some reason to actually need to use glass, then something like Pyrex will work, but even then it's putting a lot of undue stress on the glass, so you're better off just using metal in any case where you don't really need transparency or the like.
    – Matthew Najmon
    Commented Jan 27, 2019 at 15:07
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Two things to be careful of:

  1. The bowl mustn't reach the water (or even be heavily splashed).
  2. In some cases the side of the pan (assuming the bowl is in a saucepan) can heat a ring of bowl. This probably isn't a good idea. Keeping the heat low and making sure the pan doesn't boil dry can help a lot. A thin insulating spacer (folded baking parchment or similar) should stop this happening too.

In general bringing the temperature up gradually is sensible, and not putting cold liquid into the hot bowl. You may have simply been unlucky.

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  • If the bowl isn't sitting down in the water, then that's not a double boiler, hence not relevant to the question at hand.
    – Matthew Najmon
    Commented Jan 27, 2019 at 22:23
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    @Matthew I'm afraid you're wrong there. The point is to heat it with the steam not by contact with the water
    – Chris H
    Commented Jan 27, 2019 at 22:27
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    That's not what's being discussed here. What you're describing is a different type of cooking. "Double boiler" doesn't refer to what you're thinking of; it refers to the inner pan being immersed in the heated water contained within the outer pan.
    – Matthew Najmon
    Commented Jan 27, 2019 at 22:34
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    @Matthew you may be able to use that definition sometimes, but thespruceeats.com/what-is-a-double-boiler-995647 agrees with me. marie Among many results that support my meaning, this was the first.
    – Chris H
    Commented Jan 28, 2019 at 6:50
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    @MatthewNajmon that's an American link, but it matches the use I know from Britain. I won't get involved further in a discussion over the semantics, or the effects of a method I have no experience of and regard as a wrong interpretation. Feel free to write your own answer based on the meaning you understand
    – Chris H
    Commented Jan 29, 2019 at 21:21
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Get a proper tempered glass bowl or use a metal bowl.

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