There’s a post I saw on reddit that points to the dimple on the side of a milk jug, and makes fun of all the people who don’t know what that’s for. In the comments are thousands of people giving dozens of different explanations, and all of them are wrong.
It is not there to indicate that the milk has spoiled by popping out due to gasses produced by spoiled milk. If there was enough gas to pop out the dimple, the whole jug would look like a balloon.
It is not there to provide structural integrity, like lateral support to prevent the bottles from crushing. The contents are under pressure, so if there was enough force on the jug from any direction, then the cap would pop off regardless of the shape in the sidewall.
The actual answer is that the dimple is added to ensure that all of the jugs contain the same volume of milk. Plastic jugs are blown into molds, and minor manufacturing variations over time would create jugs that hold different amounts of milk. Larger jugs would hold more than a gallon. They could just fill by volume, but consumers are wary of purchasing a bottle if it appears to be less full than the others. So they add the dimple to make it so that the level of milk is all the way at the top with minimal air between the milk and the cap.
You can verify this yourself by finding different jugs from the same supplier with dimples of different depths, or even no dimple at all. None of those other explanations would explain dimples of different sizes or jugs without dimples.
TLDR everybody is wrong. The milk jug dimples are added to ensure the jug contains the correct volume of milk.
Very fascinating, so much so that i don’t think it belongs in lemmy shitpost
The contents are under pressure
You buy carbonated milk?
huh wow. i was going to presume it was a storage volume quantity calibration of some kind. neat.
Aren’t moulds manufactured to incredibly high precision? I can’t imagine them having imperfections big enough to cause visibly different fill levels.
However, my only qualification is hundreds of hours of watched How It’s Made episodes so I might be completely wrong.
You’re more qualified than me, I’ve only watched How It’s Actually Made
The dimple was there for stress releif:
Combined with the octagonal shape of the container, the circular, concave indent on the side of a milk container increases the stability of the plastic, allowing the internal pressure to disperse evenly. This improved structural support also allows jug manufacturers to reduce the amount of resin needed to make each container.
Read More: https://www.sciencing.com/1865028/milk-jugs-dimple-reason/
That very same article also does say however:
On top of that, the indentation allows the manufacturer to precisely control the volume that the jug can hold.
OP said it was not for integrity, which is wrong because it is for multiple things including integrity.
Right, but the person I replied to said it was for stress relief [only] - as if to invalidate by omission the original assertion that it’s for controlling fill level.
I pointed out the article supports both positions, and I did that for the benefit of people who might not read the article to see as such, and would otherwise take the comment to mean the article is in complete contradiction to the OP rather than partially contradicting and partially agreeing.
I don’t really have any personal stake or care about who as individuals are right or wrong in this, but I would like to get to the bottom of the milk dimple mystery. On that basis I’m not sure I know the truth even after reading the article, because it seems to be one of those things with a lot of myth behind it and not a lot of definitive sources.
I don’t mean to be rude, op, but I just straight up don’t believe you. This just doesn’t make sense.
That’s fair. You can believe what you want. But that doesn’t make it less true.
checks the community I’m in ohhhhhhh I’m a dumbass, of course that’s what it’s for
What exactly doesn’t make sense about this explanation?
First of all, the problem it’s claiming to solve doesn’t make sense, you’re not going to have enough variation in jugs to have a noticeable variation in the fill height of a gallon. Even if you did, for this solution to work, you’d have to be putting the dimple in it while it’s filled and unsealed, which would be extremely difficult. On top of that, you’d have to vary the depth of each individual dimple for that bottles exact level of fill, adding extra challenge on top. Even if the problem as op describes it was occurring, it would be a fuckload effectively cheaper to just have some jugs look slightly underfilled than add this ridiculous step to the packaging process. Hell, it would be cheaper to go make your jug blowing process more reliable. It just doesn’t add up. I’m not saying op is necessarily lying, they could be misremembering what they learned and be earnest about it. I could still be wrong too, but from what op has conveyed and how I’ve understood it it doesn’t make sense.
I didn’t know that was some ofdd affair I can care this little about.
Not quite accurate. The indentation is there for a few reasons. Source: https://www.sciencing.com/1865028/milk-jugs-dimple-reason/
I would not know our milk comes in tetrapaks.
Sweden?
Nah you’re way off
South Africa?
That is even further off. It is in europe and you did get the first letter correct both times somehow.
Scunthorpe?
you have been banned from Call of Duty chat
Hell nah
Slov*ia? XD
Yeah just clear up the asterisk
Southern Poland?
And liters
The way the old Norse gods intended it to!
It would be the slavic gods in my case. Svarun be praised
Mine comes in bags.
I always thought it was to help prevent it exploding if dropped. I’ve dropped a gallon a couple times and the dimple pops out and the lid stays on. Kinda like an air bag.
It adds flex to the container for variations of atmospheric pressure. It’s what they mean by the fill levels.
Milk containers are filled by weight. The exact volume of the liquid can vary slightly based upon the atmospheric pressure.
If the container has no flex the top will pop off or the sides will crush in with pressure changes say when a truck drives over a mountain pass to deliver the milk.
The brand we used to buy would put their label there so it was protected from peeling off, Or rubbing against other jugs in transit. Things can have multiple purposes
So how is the dimple added after filling? If it’s to ensure a common fill amount, it would have to be done post-fill.
At least, I can’t figure out how it would be done pre-fill without somehow precisely measuring the volume of the empty jug.
It’s assumed that all jugs from a mould hold the same volume, but not every mould holds the same volume, so by aiming high for the initial design of the mould and then adding spacers to the side of the mould as needed you can achieve a modified mould that stores the correct amount.
It’s added after molding the jugs and the volume is checked, but before the milk is filled.
That’s a ton of manual labor on a disposable container. Manual labor is extremely expensive, and plastics manufacturing is extremely repeatable and extremely cheap at scale (that’s kind of the big reason plastic is so common, it’s cheap and reliable)
Granted I could imagine a machine which fills it with dyed water, uses a camera to determine the fill level then passes to another machine which adjusts by volume but that’s really going to slow down the production line doing all of that.
Ultimately plastics manufacturing is way more precise and consistent than that, you’ll basically end up with either a milk jug or a misshapen mess if there is a defect, and not really anything in between
So the mold is made, the volume checked, adjusted via an insert, and then they crank out jugs.
That’s plausible, but over-complicated in an age of digital CAD and mature molding techniques.
Sounds like milk bags are vastly superior.
Apart from when you want to use them.
Spoken like someone who’s never used them.
Milk specifically, no, other bagged liquids, yes. An absolute pain in the ass compared to a bottle.
If you have the right milk bag holder, it’s seriously a non-issue.
The only non-milk bagged liquids I’ve had were IV, and a nurse dealt with them, not me.
I mean your original argument was it was more convenient - everyone having to buy a milk bag holder already seems less convenient than one guy inserting a few shims in a few moulds every couple of months.
Have never even really noticed them in west coast Canada’s 4L milk jugs (215 mL/7.25 oz more than a gallon). I’m in bagged milk land for the holidays, so I can’t check right now.
Cool fact, makes sense and it is absolutely trivial but interesting. Thanks!
No I never thought to ask about it. But it’s good to know, I guess?
