Is there any purpose for the indentations on 2 sides of a plastic milk jug? Our family was wondering this tonight at dinner. I thought it was because it was a way to make that much more profit, but I figure there must be a better reason.
If this was asked before, forgive me… I couldn’t find it.
Seems like ergonomics to me, although I couldn’t find any proof to back that up.
Shouldn’t be for money making. A quart of milk is a quart of milk.
The reason plastic milk containers have those circular indentations is to give the vessel added strength. They redirect stresses along several different smaller surfaces, making the walls of the jug more rigid.
Give me a break Astroman. Just how strong do you think a milk jug needs to be?
I don’t know about you, but my local grocer does just fine by stocking those flat sided cardboard containers of milk. I don’t think carton failure is that big of an issue with him.
If it does fine with cardboard, it should be the same, if not better, with plastic.
If you ask me, I think it’s an issue of production. That is, it has to do with packaging and the mechanization of the process. It’s something for the conveyer to latch onto.
I’m serious. this is the same reason corrigated cardboard boxes are made the way they are.
That’s not the issue, nor is paper vs plastic. Every mass production process involving bottling has to minimize the weight of the bottle as much as possible without making it too thin to use. If they had to make the jugs thicker, it would take more plastic, and more plastic times a few million jugs equals spending a lot more money.
The jugs are JUST thick enough. A few of them break or spring leaks in transit from time to time, but not enough to justify the extra cost of thicker jugs. Believe me, bottling industries have armies of production engineers to judge these things.
For whatever it’s worth, I think we’re all wrong. I hope someone comes along with the right answer.
Until then, I retract my, “Give me a break” comment towards Astroman and re-direct it towards MC. ‘Expansion joints for possible fermentation’.
That’s rich, MC.
But not for fermentation. I believe they are there in case any outside pressure is applied to the jug i.e if the jug is dropped or if jugs are smashed together while processing or shipping them.
… make sense to me, and I must admit, I don’t know why they are there either. However, until we get the definitive answer, C-Note, why not refrain from the “give me a break” stuff? You yourself put forth the proposition that the indentations are production-related, but even you don’t know for sure, so give us a break, huh? 
BTW, welcome to the SDMB, Astroman.
Thanks,
Quasi
Just noticed Astro’s been with SDMB since 7/2000. My error, sorry! :o
Q
To save money on raw material plastic jusgs are thinner to the point where they would develop an outward bulge at the center of each face. The comparison with cardboard is not valid for two reasons, one is that the cardboard is much stronger and another is that the side of a one gallon milk jug is much bigger in surface. The conical inward indentation breaks the bulge and provides a little reinforcement. The bulge itself would probably be no big deal as the jugs could still be transported etc the same way. Probably the main reason to get rid of the bulge is aesthetics: people will buy the jug we know over one with a bulge all around it which looks cheaply made. The intentation make it much more aesthetically pleasing and would marginally help in stocking them in shelves closer together.
I’m going to have to agree with the expansionists here, but disagree on the primary cause for expansion. Remember, milk is mostly water, which means that it expands when it freezes. I’d imagine that milk is allowed to freeze a lot more often than it’s allowed to spoil in the jug.
If the plastic were really so flimsy that strength would be an issue, then all of those annoying dents the jug gets would just pop right out on their own.
Perhaps it is so that if you drop it the indentation will
pop out instead of the container bursting open in some way?
Chronos, can you provide any examples when freezing milk was ever a problem in manufacture, transport or retailing? I do not think you can find one. Have you ever had a problem at home with milk freezing? Anyone else you know? No? I didn’t think so.
As the only person around here who has had problems and experience with milk freezing I can tell you the indentations would be quite useless. After all, milk jugs did not have them when they were thicker and did not seem to need them. Milk is not water. When it freezes it does not freeze like water into a solid block which will expand but rather as slush first with small crystals. Even water would probably not burst a palstic jug without indents. The 1/2 gallon jugs have no indents. I freeze water in all sorts of containers all the time (for the icebox in the boat) and never had a problem.
I have seen cheap generic sodas in very thin containers which do not keep their shape well and they look… well… cheap.
I still think my post above gives the real reason.
Off topic-
Wow. Two threads in a row where I’ve been reprimanded by fellow posters for my behavior.
The “Give me a break” comment wasn’t meant as mean or in your face. It was meant to be more conversational than anything else. That is, it’s something I would have said in person without giving it a second thought- the other person would know it was meant as a figure of speech.
I certainly didn’t mean to snub ya Astro. And welcome aboard.
I’m off to find out what other bad things I did this morning…
But before I go, I still don’t buy, err, agree with the expansion theory. It doesn’t make sense to me that the milk would be expanding that much unless it was fermenting.
I still believe it has something to do with the packaging process. Something with conveyer belts or robots…
I’m right I tell ya, I just need some corroboration!
Woops. We all seem to think you just joined Astro.
The welcome still stands, just make it a welcome back.
Ummm yeah…we have milk delivery here in Saskatchewan and in winter when the temperature reaches -20F -30 C the milk does freeze…and the indentations do fill out…
Keith
I work in grocery as well and have spent a lot of time with milk. And as far as I can tell the expansion idea is the best one. I have seen the bellybutton (thats what we call it) popped out in all the senarios discussed. I’ve seen it freeze and spoil with the “button” popped. The thing with it spoiling, like most things, the milk gives off gases. It’s the air that pushes the indent out. It also keeps the jug from breaking in short drops, but usually a fair distance will still break the jug.(Clean up in aisle 16!)
Also, we call popped jugs outies and the regular jugs innies.