# Why are there holes in ice cubes in airplanes?

It could be due to boredom that I notice this, but it seems that only on airplanes ice cube have holes. Why is that?

• I have seen those in bars and restaurants too, I believe some machines are designed to produce these holes, apparently they have some advantages. Usually they are also cylindrical rather than cube-shaped. – Relaxed May 19 '14 at 16:05
• I bet it's a choking thing. If I accidentally swallow a cube like the kind you are speaking off, I can still breath through the passage easier then a whole brick. – John Riselvato May 19 '14 at 16:10
• The reason is probably most trivial: greater surface area allows for a greater rate of cooling. Holes are a neat way to increase surface area without increasing overall dimensions of the ice cube. – mindcorrosive May 19 '14 at 16:11
• This question would get more detailed answers on Physics SE, but I wouldn't go so far as to say it's off-topic here. – R.. May 19 '14 at 17:14
• Airlines are a special case here compared to other outlets. Airlines need to maximise speed of service, and of clearing away. In fast food it is OK to provide loads of ice and less drink - while that may result in lots of unwanted and unmelted ice being left, they don't care. It is much slower and more difficult to clear away lots of tumblers which have ice left in them, than empty ones where the optimum amount of ice has been served and melted, so the latter is better on board aircraft. The greater area that promotes rapid cooling of the drink, by definition also warms and melts the ice. – AdamV May 21 '14 at 11:47

They have the holes because of the machines that made them (check DavidG's answer), anyway this ice cubes with holes are better for planes for a few reasons:

• Because they are lighter (believe it or not, every gram in the aviation business counts, plus the ice is not made onboard, it is loaded prior to departure just like the food)
• They cool things faster due to larger area of contact with the liquid
• They also will allow more liquid to be filled in the already small airplane cups.
• Last thing, they do not tend to stick together in the ice bucket, so cabin crew won't need to smash it to break it down.
• It also takes less energy to produce them (less volume/mass of water) for the same cooling power (surface area). On the other hand, it means you end up giving customers more beverage/less ice, which might have a cost in itself. ;-) – R.. May 19 '14 at 17:13
• they can also be made clear because the freeze to the rod from the inside out so the ice has room to expand out rather than cracking when freezing from the outside in – ratchet freak May 19 '14 at 17:58
• @R.., On many flights, I receive the entire can (355mL?) It's not true of every airline, but it's common enough. So more beverage/less ice is not necessarily an issue. – Brian S May 19 '14 at 18:15
• Can you explain briefly why they do not stick together? – Daniel Wagner May 19 '14 at 22:16
• This is incorrect - your answer merely lists side effects. DavidG has the correct answer. – Rory Alsop May 20 '14 at 13:22

In the retail drinks trade (pubs, bars etc), machines that make these hollow ice cubes are often* used where there is not much room to store large quantities of ready-produced ice (such as in a much larger machine). The larger surface area to volume ratio means fresh ice cubes can be made more efficiently and quickly to meet demand - by the time one batch is used, the next is ready. The ice machine only needs a small storage capacity at a time to keep up.

*Of course, in warmer climates where ice is used in larger quantities, or in establishments where drinks depend on more ice (cocktail bar versus English pub), they will usually have larger capacity machines, but even then the hollow cube is common.

It's because the machine that creates the cubes has metal prongs that the ice 'grows' around.

• This is the correct answer. The most efficient ice makers (and the majority of industrial ice makers) are not those that cool the surface, but those that use refrigerated metal prongs that stick down into the water pool. As the water freezes around the prongs, they rotate out of the pool and deposit the ice into a vessel. – Rory Alsop May 20 '14 at 13:21
• +1 for detail. This is part of the point I was making without discussing the mechanics of the machine - the "surface" in this case is not the "outside" of the cube, but the inside. It comes down to the least distance between the cooling part (the "prong") and the outside of the cube. A thin wall will be more efficient to cool than a solid lump – AdamV May 21 '14 at 11:36
• But why do airlines use this machine whereas ice cubes we encounter in many other places seems not to be made with a similar machine? – hippietrail May 21 '14 at 15:23
• @DavidG: Which, in turn, lead to more questions: Why do airlines buy ice making machines that most other places serving ice do without? Why do airlines choose the less expensive of several available ice making machines which result in different shapes. In any case your answer makes it seem like a total coincidence in which the airlines definitely play no conscious decision making part whatsoever. Which is fine if it's true, but you don't show that it is actually true. – hippietrail May 21 '14 at 15:40
• I have to vote this down because it focusses arbitrarily on one point in a string of causes and effects and decides it is the "correct" one, with no justification, in a one-sentence answer. – hippietrail May 26 '14 at 13:26

Typically those are used to identify ice cubes made from drinkable water. Restaurants use them in most parts of the world and those are not limited to planes. Actually, we were at a steakhouse just yesterday and my smallest daughter asked exactly the same question. She probably was bored too.

The comments to your question are interesting because they outline several advantages of these. Risk of choking being reduced is a great one. Obviously cost saving and efficiency are important too.

• "from pure water"? What else would ice cubes be made from? – Greg Hewgill May 19 '14 at 20:17
• It could be not drinkable water — or less enjoyable (i guess that's what he meant) – Jay Claiton May 19 '14 at 20:27
• Yes, sorry, the term is not universal. In many parts of the world, where tap water is not drinkable, they call the one that is pure water or the equivalent expression in the local language. – Itai May 20 '14 at 1:11
• Oh, so you might have one kind of ice cubes that you put in a bucket to keep (unopened) drinks cool, and another kind of ice cubes that are made from drinkable water that you can put in drinks. Makes sense, thanks. – Greg Hewgill May 20 '14 at 2:30
• @Itai maybe for air travel, but for the general food and beverage industry they are probably more expensive. It's definitely better to use solid cubes. Water is cheaper than any average drink. I never witnessed this case, but I worked with this industry and I can assure these things are measured to the cent. – nsn May 20 '14 at 15:27

The surface area is bigger when it is hollow. More the surface area means that it helps cool the drink faster.