What material is best suited for eating ice cream from, without the ice cream melting too fast on the edges?

Question

When I buy some ice cream from a parlor or get some from the supermarket I find that the containers (also the standard bowls I can find in my kitchen) are not perfect for eating ice cream from. The problem is that the ice cream already starts to melt on the edges and on the bottom when eating it from top to bottom. I'd like to eat my ice cream from top to the bottom of the container without having to worry about the edges getting liquid.

I know that the shape of the container (how much surface area it has) is important too, but from what I as a layperson understand the thermal conductivity of the material is much more of importance in this scenario. I already searched the internet and found some comprehensive lists of different materials and their thermal conductivity but those lists don't really make a difference between food safe or not and apparently thermal conductivity also changes with the temperature of the materials.

My last physics lesson was over a decade ago and I have to admit I'm simply lost. What I'm looking for is the material best suited to put ice cream in and the ice cream should melt considerably slower on the edges than the top that is exposed to air. The material should be safe to eat from, and it should be possible to actually make an affordable bowl from it (i.e not made of diamond). I assume an room temperature of 20 °C (or maybe 35 °C on a hot summer day).

The best I could come up with so far, although more from experience than based on science, is a wooden bowl.

Answer 1

Why not put the bowl in the fridge or freezer before so that it is cold?

There is an interplay here between heat conduction (how fast the bowl equalises temperatures between ice cream, bowl material and air) and heat capacity (how much thermal energy is in the bowl, ice cream and air). If you had a bowl with a great deal of heat capacity and a low initial temperature (say a thick porcelain or marble bowl you had put in the freezer beforehand) then it would help keep the ice cream cold, but the same bowl at room temperature would of course just act to heat the ice cream to room temperature more efficiently. One interesting approach is of course to freeze ice into bowls - low temperature and a big heat capacity (maybe even too large; in my opinion ice cream should not be served too cold).

A bowl with small heat capacity and low thermal conductivity would itself not contribute much to heating, but would keep the ice cream insulated from the air and body heat. One approach would be a thin metal bowl (small heat capacity) surrounded by something fluffy (low thermal conductivity), perhaps held in some further convenient shell (like another metal bowl, or a wooden bowl). Think of how a thermos flask works: there is an insulating layer of air (low conductivity) between two metal shells (themselves kept in place using rubber or plastic fittings).

Diamond is a pretty bad ice cream bowl because of its high thermal conductivity and relatively large heat capacity; always chill diamond bowls before serving!

Answer 2

Use a thermos flask with a metallic inner side.

Things that keep hot stuff hot are usually similarly good at keeping cold stuff cold, since the goal is to prevent heat transfer which works both ways. When searching for something good at keeping hot stuff hot, we'll quickly think of the separation of surfaces in a thermos flask (or vacuum bottle).

The thermos flask consists of an outer layer and an inner layer separated by vacuum (ideally). When pouring cold stuff in, the inner layer will is the only layer in conductive contact. The vacuum prevents conduction or convection of heat from the outer layer since there is simply no material to carry the heat across the gab. Only thermal radiaton remains, and this can be reduced strongly by making the inner layer shiny on the surface towards the gab (such as the back side of regular aluminium foil).

Is vacuum not possible in a practical application, then use a filler material between the layers of lowest possible thermal conductivity. Insulation in housing is optimized for this purpose, and some sort of wall foam (maybe actual mineral/glass wool) would be perfect. This may be overkill for your application, and everyday thermos flasks usually also just use air, which in itself and when stationery is very insulative. But any breach may cause air not to be stationary since it can flow in and out of the gab, causing convection.

When heat transfer from the outside is dealt with and prevented, only the inner layer itself can still cause melting. It will do that by transferring its contained heat to the ice cream by conduction until it has reached the same temperature as the ice. Therefore, make that inner layer of a material with a very low heat capacity, so that very little thermal energy is "stored" in it.