Question about the heat rention of water

I’ve been thinking of placing a shallow steam pan (filled with cooked food) inside a deeper steam pan (filled with hot/boiling water) to keep food warm longer. This might come in handy for parties where food sits around. The pans would not be connected to any heating element. So when the water in the pan cools down, I would simply replace it with more boiling water.

I’ve been wondering about how deep of a pan I should use for holding the hot water.

So my question is: Will a deeper pan filled with more hot water stay warm longer than a less deep pan? In other words, does the volume of hot water matter?

It will matter, but depends on a few factors (and I’m so, so far from being an expert in physics). The specific heat of water means there’s a total cap on energy water can retain, so overall heat/energy can only be increased by using more water (setting aside things like superheating water). There are other considerations like surface area of the deeper pan, exposed surface area of the water to the air, and other heat transfer based topics, but the short answer is yes, the volume matters.

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Thanks. The water won’t be exposed to ambient air, as the two pans would be the same size (except for depth) and fit snug inside each other. The rim of the top pan covers the rim of the pan below it.

I have some 6" deep steam pans I could use for the hot water. Then I have some 2.5" deep pans for the cooked food that fit inside those. That leaves room for around 3.5 inches of hot water in between. But I also have a 4" deep pan, which would leave room for about 1.5 inches of hot water in between.

I’ll need to buy a few more pans as I am also thinking of double jacketing the bottom pan (using two pans inside each other to hold the hot water) in order to insulate the water better. 6" deep pans are more expensive than 4" deep ones. So that’s why I was wondering whether it would matter how deep the pans are (and thus how much water is optimal).

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Another option might be to bring water to a boil in a cast iron Dutch oven, like a le Creuset, then place the pan of cooked food in the hot water, cover with lid if possible. Wrapping the DO in a towel will also help retain heat.

(This is the method I use for making yogurt. Works a charm.)

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Sure, but for dinner or back yard parties I would be serving 4 or 5 hot dishes, all needing to be kept warm. I have le Creuset pots, but only one large one.

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Yeah, unless the cost difference is really significant, I’d go for the deeper pans…it’ll save you from having to add more hot water as much, when you should be enjoying yourself! (Or, a couple Sternos to keep it warm too - they are pretty cheap!)

If you’re purchasing more pans for this you also might want to consider plastic cambros for the water reservoir because 1) they’d provide better insulation and 2) in the event you don’t need extra hotel pans.

A couple caveats are they don’t look super great and I can’t remember if you can nest hotel pans in them comfortably. Theoretically, if you could nest a plastic cambro in a hotel pan that might cover the first issue…?

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Quite right.

A deeper pan with more hot water will stay warm longer
Heat insulation around the larger pan will help further retains the heat (less heat loss to the environment).

Thanks. I’m looking for the least expensive solution. Buying a cambro seems like it would cost more than buying a few hotel pans with lids. I wonder if plastic hotel inserts would be cheaper than s/s.? Plastic inserts may not keep the food as warm though.

Sorry, I should clarify I was referring to the equivalent of plastic hotel pans like this (included for clarification, not an endorsement). I forget that Cambro is frequently used to refer to an insulated holding box!

As far as keeping the food warm, plastic would insulate better than metal. I can’t remember the exact science of it (I think it has to do with the heat capacity and thermal conductivity…?). To give a practical example, that’s why it’s generally recommended you sous vide in a plastic reservoir rather than a metal one since the metal will not insulate as well so more energy will have to be pumped in to maintain temperature.

Interesting, thanks so much. So I’m now wondering if it would be better to use the plastic polycarbonate for the top food container, or for the bottom hot water container, or both?

Sorry, one additional warning: if you’re relying only on hot water to maintain temperature (no sterno burner) then you should probably also make sure the food pan is touching the water in the reservoir. I’m just spitballing here but in a normal steam table the steam (which has a very high heat capacity and conductivity) is “touching” the food pan and transferring energy. In contrast, without steam hot water will conduct heat well enough but if there’s any air gap between the water and the food pan much less energy will be transferred.

Again, to give a practical example, think about holding your hand in an oven at 200F as opposed to a sauna at 200F. You’ll find you can hold your hand in the oven much longer than the sauna because the former is mostly conducting heat with hot air and the latter is conducting heat with steam.

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I thought steam was hotter than the boiling water producing it?

Good question! First, I don’t believe plastic hotel pans are usually used to hold hot food but I could very well we wrong about that- it’s been years since I’ve worked in food service. If that is typical then hot food held in a plastic container would theoretically maintain temp better if there’s a lid. However, it will also insulate it from the hot water in the reservoir so it would likely be a wash.

I believe that’s the case as well but it’s been 15 years since I took a physics class so don’t quote me on that! Likely more significant for your specific circumstances are what’s touching the food pan and what that pan is made of as discussed above.

As I write this, I am experimenting in my kitchen. I just boiled up some water and poured it in to a 1/6 size single hotel pan with a lid on it. Started off at 200°F. 40 minutes later, it’s at 160°F. So pretty good retention so far. I wonder how hot I would need to keep the water?

I figure keeping the food warm for 1 hour should be enough before refilling with boiling water.

My thinking is I would cook up a dish, then when it’s almost ready, have a batch of boiling water ready to pour into the deep bottom hotel pan. I’d pour the boiling water in, then place the finished cooked food into a shallow insert pan with a notched lid and a serving spoon. Nest the shallow insert pan (with the cooked dish) on top of deeper pan with boiling water. Then carry the pan(s) to the dining table and place on a trivet.

When someone asks to pass the dish over to them, lift the insert pan out of the deeper pan and pass along (lifting both pans would probably be too heavy when seated at a dining table). This will expose the boiling water to ambient air for a half minute or so, but I don’t think there will be significant heat loss.

I think that could work with the caveat that the shallow (cooked dish) pan should be in contact with the boiling water. This is where I’m really far out on a limb, but I think once you put the boiling water in the deep bottom hotel pan it would lower the temp below boiling and only go down from there. The upshot of that is, if the shallow pan is not touching the water then it will only be touching only remnants of steam and mostly heated by air that is heated by the water which would transfer much, much less energy.

Maybe I could use perforated insert pans to allow for steam to pass directly through to the food? (this might not be possible for dishes that are more liquid)

Okay, so I just checked the temp again, and after 1 hour, the boiled water has cooled to 153°F. I may not need to double jacket the bottom pan after all. But I’d need to figure out how this temp translates to the temp the in the food in the insert pan above it.

Bingo! That’s really the whole issue. Typical steam pan setups with sterno are simple but extremely reliable because it uses constantly heated water to generate steam which transfers heat very well and is more or less the same constant temperature which addresses a few issues at the same time. It’s the same reason a double boiler is also useful for stuff like melting chocolate.

Perf pans are great for that but keep in mind that you have a finite amount of steam that will dissipate and not be replaced any time the lid is lifted.

“Food is a pretty good prism through which to view humanity.”

― Jonathan Gold