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I was baking bread for the first time in years the other day, and the instructions said put a baking tray full of water in the bottom of the oven. I didn't have a metal baking tray, so I put a ceramic ovenproof dish in the oven, and let it warm up. Then I boiled a kettle and poured it into the dish. DISASTER! The dish cracked immediately, spilling water into the bottom of the oven.

Obviously this was a dumb mistake. Next time I'll use a deep metal baking tray etc.

However, I'm trying to understand why this happened, because when I make a stupid mistake I like to fully understand what went wrong. I wouldn't have thought the temperature differential between the ceramic dish and the boiling water was sufficient to cause the sort of rapid expansion that would cause this to happen.

Any insights?

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    What was the oven set at when warming the dish? Note that the temperature difference between boiling water and a room temperature dish (100C vs 20C) could be about the same as between boiling water and an oven-temperature dish (100C vs 180C). The water may have been too cold, resulting in rapid contraction.
    – Nuclear Hoagie
    Commented Jan 31, 2022 at 15:30
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    Indeed, if you think about it, pouring 100*C boiling water into a dish at 200*C is subjecting the material to the same temperature difference as pouring a boiling water on your car windshield to thaw it when it's 0*C outside. Don't pour boiling water on your windshield, by the way; they're a lot more expensive than an oven dish..
    – Caius Jard
    Commented Feb 1, 2022 at 9:04
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    Maybe somewhat off topic but I'm not sure why you didn't just put the ceramic dish in with the water? Why did you feel the need to heat the dish first?
    – JimmyJames
    Commented Feb 1, 2022 at 18:12
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    If you want to get steam to influence the texture and taste of the crust, consider looking at Jim Leahy's "No-Knead" bread recipe (lodgecastiron.com/recipe/jim-laheys-no-knead-bread - or you can buy Leahy's book). He cooks the bread in a cast iron or ceramic-coated pot. The pot lid traps in the moisture escaping from the bread as it bakes and super-heats it. It make for a great crust.
    – Flydog57
    Commented Feb 1, 2022 at 22:48
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    If it makes you feel any better, when I was a few years out of college, I did this exact same thing, but with a Pyrex glass baking dish... if you've ever broken anything pyrex, you can imagine what happened next. I don't think we ever got all of the glass out of that oven... just glad I was able to get out of the way before the boiling water came out!
    – Joe M
    Commented Feb 2, 2022 at 18:08

2 Answers 2

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You have answered your own question, it was the rapid change in temperature which caused the ceramic to crack. Oven temperature for bread baking is usually somewhere around 200°C/400°F, whereas water is 100°C/212°F, which is not a trivial difference. Everyone thinks boiling water is hot, but it's cool compared to a hot oven. Rapid changes of temperature aren't ideal for glass or ceramic.

That isn't to say that your ceramic dish should have shattered, but it isn't a surprise. Next time feel free to use a ceramic dish but put the water in it at the outset, although they aren't ideal. I prefer to use a wide metal baking tray instead because it has a lot of surface area for water to evaporate, baking dishes won't get your oven moist as quickly.

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    While metal dishes are more stress tolerant than ceramic dishes it's still stress. You're performing an under temperature quenching. Let the pan heat up with the water and it'll stay the same shape.
    – candied_orange
    Commented Feb 1, 2022 at 22:07
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    +1 “Everyone thinks boiling water is hot, but it's cool compared to a hot oven.” That reminds me of “Toaster vs. Freezer”, which points out that, while a freezer may seem far away from normal bread (in terms of temperature), a toaster is even further away.
    – Brian Drake
    Commented Feb 2, 2022 at 14:16
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Presumably the dish was pre-heated to bread baking temperature (?450F?) but the water was at least 200F cooler. Water has a HUGE heat of vaporization. It takes 5.4 times as much heat to convert water to steam as it does to bring the same water from 32F to 212F. All that heat is sucked out of the surface of the baking dish , cooling it to 212F.

Ceramics have poor heat conductance. Poor conductance means the water side of the dish cools down, but the other side doesn't. The cold side shrinks, but not the hot side. This produces a huge stress inside the ceramic material.

Ceramics have low elasticity. This means the material can't bend (like steel) so the stress can't be relieved by warping.

Ceramics also have poor tensile strength. They break when stretched.

Glass breaks in tension. It is incredibly strong in compression. "Heat proof" glassware is tempered. The tempering process puts the interior of the material in tension and the surface in compression. The compressed surface closes cracks which could start a break. But the stresses between surface and interior store a lot of energy. So when it goes, it explodes

That's why the dish shattered: Big temperature difference, big tensile stress. POP !

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  • Oh, yeah, I didn't even think about the fact that the water would be going in on one end. Good answer.
    – FuzzyChef
    Commented Jan 31, 2022 at 22:37
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    I saw a similar situation uncomfortably close at hand when at a friend's BBQ - he brought some sausages out of the house (pre-cooked in an oven at 200C) in a ceramic baking dish; after transferring the sausages to the BBQ to finish cooking, he put the dish (probably still well over 100C) on the garden path (concrete paving stones), right next to my chair. The temperature differential was enough for the dish to positively explode, showering my legs with shrapnel. No injuries beyond a scratch but one hell of a shock to the system. As in many things, it's the gradient that does the damage.
    – Spratty
    Commented Feb 1, 2022 at 9:59
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    @Spratty---Glass breaks in tension. It is incredibly strong in compression. "Heat proof" glassware is tempered. The tempering process puts the interior of the material in tension and the surface in compression. The compressed surface closes cracks which could start a break. But the stresses between surface and interior store a lot of energy. So when it goes, it explodes.
    – Woody
    Commented Feb 1, 2022 at 17:33
  • @Woody But OP tells us they used a heat resistant ceramic dish, which is different from tempered glass. OP's dish probably just cracked into a few big pieces and likely did not explode into hundreds of tiny fragments like tempered glass does.
    – J...
    Commented Feb 1, 2022 at 21:09

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