Why do the coffee mugs in diners have concave sides

May 24, 2005 10:21 AM

Why do the coffee mugs in diners have concave sides?

An hourglass shape has a high surface area compared to its volume. So coffee in an hourglass-shaped mug should get cold faster, right? Wouldn't the ideal coffee mug be sphere-shaped, to minimize the surface area and keep the coffee hot?

posted by nebulawindphone to Food & Drink (23 answers total)

Maybe it's to minimize the volume of a coffee cup. Perhaps the diners I frequent have made me cynical, but once the dinee has paid for it, who cares when it gets cold? They'd serve coffee in solid helium if it would save them money.

It'd be hard to drink from a perfect mug, and the difference in heat dispersion between a cylindrical mug and a slightly-off-cylindrical mug is laughably insignificant. It's probably simply a style that's become entrenched. Customers think of that cup style as the "diner cup" style, thus most diners get them, thus most supply companies make them in huge numbers, which makes them cheap, so only the diners most interested in having a "unique look" would get a different style.
posted by Plutor at 10:59 AM on May 24, 2005

So it's easier to hold (if you're not using the little handle)?
posted by SheIsMighty at 11:01 AM on May 24, 2005

I think Plutor is probably right. A successful design doesn't often change unless it has to. The mugs also fit most pleasingly in the hand.
posted by Dr. Wu at 11:03 AM on May 24, 2005

I thought it was because soon after you start drinking it, it has a lower center of gravity and thus is less likely to tip over.
posted by vacapinta at 11:09 AM on May 24, 2005

Makes the space between the mug and handle bigger too.
posted by NickDouglas at 11:36 AM on May 24, 2005

On this note, I think diner mugs are insanely satisfying to drink from...perfect heft, weirdly perfect width of the ceramic. I've had an unhealthy obsession with finding these for my home...outside of stealing them from a Steak & Shake or a Bickfords, anyone have any pointers where I could order some?
posted by tpl1212 at 11:38 AM on May 24, 2005

Try this.
posted by spilon at 11:54 AM on May 24, 2005

Or, if you are willing to get an account and order by the case, this.
posted by Quinbus Flestrin at 11:59 AM on May 24, 2005

tpl1212: look in your yellow pages under "Restaurant Supply". They're extremely cheap, less than a buck each.
posted by bonehead at 11:59 AM on May 24, 2005

Whoa. Wait. Can a normal guy like me go to a restaurant supplier and get ultra-cheap, utilitarian tableware and flatware in small enough quantities to merely outfit a small home?!
posted by Eamon at 12:06 PM on May 24, 2005

(Can a normal guy like me go to a restaurant supplier...)

I've never had a problem. There was one place that had a big sign that said "For the Trade Only" so I never went there, but most places have no problem.
posted by Marky at 12:15 PM on May 24, 2005

I think diner mugs are insanely satisfying to drink from

Argh! I hate how wide open the tops are. Not only from a customer-standpoint (the more the coffee is exposed to the air, the quicker it gets cold), but also having to serve them as a waiter was a bitch (larger exposed surface area = longer wavelength when they're knocked = longer time for knocks to dissipate = increased likelihood of spilling). Cylindrical coffee mugs are da bomb.
posted by Civil_Disobedient at 12:29 PM on May 24, 2005

This is such a great question! I wonder these things all the time.

Maybe it's also because a concave mug is less likely to slip out of one's hands than a straight-sided mug.
posted by elisabeth r at 1:02 PM on May 24, 2005

Best answer: so they fit in the dishwasher!

/ex-dishwasher
posted by By The Grace of God at 1:44 PM on May 24, 2005

Best answer: Stabilty on a tray and resistance to being knocked over are probably among the key reasons. The concave design assures the widest possible base, making it more difficult to dislodge from a resting position than a straight-sided mug. "Sphere mug" is a cute idea, but would be very difficult to drink from, because of the lack of a splayed lip for easy sipping. Also because when drinking from a sphere-shaped container (think snifter), once must lift the base of the vessel at a more severe angle. This can cause liquid to pool at the wide part before accumulating enough to spill over the edge, moving to faster and at a greater volume than you were expecting. With hot coffee, this would quickly become dangerous.

I think surface area/cooling worries are overblown. Once the ceramic is heated by the first cup of coffee, it becomes an excellent insulator and keeps futher pours of coffee deliciously warm much longer than cheaper souvenir-type mugs. A really good diner waitperson will fill cups with hot water from the Bunn before pouring the coffee, thus preheating your mug. Coffee handled this way stays warmer longer, offsetting any loss of heat from surface area exposure.

I reject the hypothesis that it is to minimize volume and increase profit for the diner. Coffee is one the cheapest and most expendance food products, with a very low cost-per-serving. Evidence: free refills. If diners want to nickel-and-dime you, they'll skimp on butter (several times more expensive, ounce for ounce, than coffee), syrup, fruit juices, sauces, cheeses, and meats - those ingredients are far more costly. Coffee, tea, and soda are the things they can be most generous with.
posted by Miko at 1:50 PM on May 24, 2005

Can a normal guy like me go to a restaurant supplier...

As Marky says, I've never had much of a problem finding a place that does retail as well as commercial. Many won't, but try phoning around. So they sell at 100% markup, you're still saving a bundle. I get the square green bottle-glass "French Café" glasses that I like so much that way.
posted by bonehead at 1:52 PM on May 24, 2005

expendance = expendable
posted by Miko at 1:52 PM on May 24, 2005

This shape might increase strength, but concave or not, they are very difficult to break. You can actually drive a large nail into a 2x4 using a diner mug as a hammer. I used to do this for art students as an example of the strength of stoneware.
They were impressed.
posted by weapons-grade pandemonium at 2:54 PM on May 24, 2005

I got inexpensive flatware and other restaurant supplies at Sam's Club.

My spatulas are the best I have ever had (I had a problem with the heads snapping off) and they were so cheap that I bought ten of them for less than I would pay for one at a swanky kitchen supply store.
posted by Sheppagus at 2:58 PM on May 24, 2005

The concave design assures the widest possible base, making it more difficult to dislodge from a resting position than a straight-sided mug.

I don't see how this is possible. A less spillable design would have the top either same size as the base, or smaller. In the case of a saucer-shape, you have extra weight over the sides that's not directly supported underneath, but instead is directed down to the base like an arch.

I think surface area/cooling worries are overblown.

No way, man. Wide open mugs definately cool faster than small-mouth mugs. But you're right in that the choice of material (and the thickness) is very important.

A really good diner waitperson will fill cups with hot water from the Bunn before pouring the coffee, thus preheating your mug.

If you're being served coffee from a Bunn, you're not getting really good coffee. /coffee snob

Coffee is one the cheapest and most expendance food products, with a very low cost-per-serving.

Completely agree with you on this point. Whatever the reason (I believe it's purely aesthetic, personally), it's not to save the poor restaurant/diner coffee money.
posted by Civil_Disobedient at 4:06 PM on May 24, 2005

Best answer: I suspect the answer is a practical one. The concave sides ensure that only the rims touch when they are in the dishwasher or stacked on shelves. This confines wear and scratches to the rims where they are less noticeable. In addition, the concave shape is the least likely to slip out of one's hand in soapy water. Finally, that shape is the least likely to burn the back of one's fingers while holding the cup by its handle. While it is possible to make the handle larger, that requires a disproportionately larger storage space. (I have some straight sided cups where this is a problem.)
posted by RMALCOLM at 6:04 PM on May 24, 2005

I don't see how this is possible. A less spillable design would have the top either same size as the base, or smaller. In the case of a saucer-shape, you have extra weight over the sides that's not directly supported underneath, but instead is directed down to the base like an arch.

Think physics. The concave sides create a lower center of gravity than straight sides do. Lower center of gravity = increased stability. That's true for anything (cars, people), not just coffee mugs
posted by Miko at 11:21 AM on May 27, 2005

Best answer: Yep, I'm still going with stability. That is because the economic incentive is there for stability on a tray. 4 mugs of 208-degree coffee spilling from a tray could create 32 ounces of near-boiling liquid in a customer's lap; this in turn could create major lawsuit. On a waitress' arms or legs, major worker's comp claim. On the floor, potential for slip-and-fall injuries, and further equipment damage from things that break when someone falls.

The other benefits of the mug design (easier/more comfortable to hold, less wear in the dishwasher) are side benefits resulting from a design that is intended to afford a measure of protection from accidents potentially costing thousands of dollars.

When I suggested fears of faster cooling were overblown, I wasn't saying that the coffee didn't cool faster in a wider mouth mug. Just that it's not worth worrying about, and that any loss of heat is quickly offset by the insulating properties of the thick, dense stoneware once it comes up to temp. In fact, I suggest experimenting with the two types of mugs. Fill each with the same temp coffee. Measure 5 minutes later, then 10 minutes later. I wager the ceramic mug will be warmer longer despite the wider mouth.

And good coffee from a Bunn? I'm the worst coffee snob there is, and Bunn's don't make a bad brew. Almost any home coffeemaker produces worse coffee than the Bunn. it's not the machine, which works perfectly; it's the quality of coffee put into it that matters. Anyway, who said diner coffee was supposed to be good? It's diner coffee. We were talking about heat, not taste.
posted by Miko at 11:27 AM on May 27, 2005