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.
The really clever solution is to bag milk:
YOUR MOMS BLOWN INTO MOLDS!
deleted by creator
We have plastic bags
I’m in Western NY, the “fancy” milk comes in glass bottles while the “store brand” is in these plastic jugs.
I buy non-dairy milk though which comes in cartons.
I’ve never seen a glass bottle of milk outside of old movies, around here it’s plastic jugs and the “fancy” stuff comes in cartons
So this is how I find out I’m poor…
A lot of the glass bottle companies also recycle the bottles, so that you can swap your existing glass bottle for a new bottle and they’ll take your old one back. It adds a little bit of logistical complication to the stores that deal with it, but it could be useful if you’re really trying to reduce plastic usage and you drink a lot of milk.
America fuck yeah
Comin’ again to save the motherfucking day, yeah
I’ve been using plastic bags for a while now. The difference in use is minimal, but I think the plastic difference is big.
I don’t think this is correct and would need to see a source before I believe it. I doubt the dimple is adjustable in the way you’re describing.
The amount of wear needed to change the volume by a noticable margin would be quite significant. Surface finish of the mold would be degraded enough that they would probably scrap the mold before using an adjustment like this as the mold would have sticking problems.
It might be volumetric compensation, but I doubt it’s directly wear related.
The mold is going to be at least two parts that split to get the blown jug out. The jug feedstock probably starts as a molded tube blank with the threads already in it. Would look like a test tube with a milk jug mouth.
Thinking about it, and I suppose you could actually call it wear compensation. Machine the mold with max dimple present. As your parting faces/lines take damage, you reface, and take some off the dimple to compensate for reduced volume. Maybe. That’s my best guess if it isn’t structual. Usually the rest of the mold has taken enough damage/wear that you’re scrapping the entire thing.
Believe it or not, @themeatbridge@lemmy.world is correct, just not about why. It’s to adjust for differences in jug size caused by temperature.
Plastic jugs are made by blow molding, where a tube of plastic is warmed, then inflated within a mold using compressed air to create its shape. In winter, the air and environment are cooler so the plastic is also cooler and accordingly a bit less elastic while getting blown. This results in jugs that contract a bit more while cooling and are a bit smaller. To compensate, cool weather jugs have a shallower dimple. The alternative is either warming the air or warming the molds more, both of which cost more, while this actually slightly saves money by using a bit less plastic. The converse is true for summer jugs - bigger dimple, warmer air - as the warmer plastic molds more easily.
The dimple also adds a bit of structural stability, so the jugs can be made of slightly thinner plastic. These factories pump out millions of jugs, so even a $0.005 saving per jug adds up.
I actually did some work for a company that makes plastic containers, so I got it straight from them. Otherwise I’d provide a source. What I could find online that corroborates is low quality local reporting, so I didn’t bother with URLs.
That makes more sense. Nothing to do with wear. I guess the dimple would be a removable insert. You could have a selection of them and swap when calibrating the line.
I would think that blow mold is happening right before washing and bottling. Tube blanks are probably supplied in Gaylord’s coming from the plastic producer. Transporting semis full of empty jugs doesn’t make sense.
I’m suprised there is that much variation in volume, I would expect the temps to be more consistent. I guess the compressed air temp is the main variable, mold temps should be pretty consistent. Ambient air temp when the bottle is cooling probably also plays a role, more or less shrink before it “freezes”. Not sure if they’re made from LDPE or HDPE but those are both really stretchy, so I guess they very well could jump all over on size.
Most of my mold experience is in automotive, which is going to be a tighter process.
Ambient air temp when the bottle is cooling probably also plays a role, more or less shrink before it “freezes”
Yeah I agree with that. Also maybe inconsistency with the plastic batch.
But also milk jugs are blown directly from pellets, no threaded blank. Water bottles and pop bottles go from threaded blanks though.
I don’t remember seeing washing but I guess that would be on the filling side, (jugs are made on one side of the plant then go through a wall to the clean side) I don’t think I’ve seen that for milk.
You’ve got it! My work was about sustainability, but that includes plastic consumption, so I learned about the factors that affect the amount used. You’re right on the process - they’re gross immediately after molding, so washing is next. The molds are water cooled, so they’re pretty consistent, it’s just heating the tube and the temperature of the compressed air that’s affected the most.
The volume change is unintuitively high. Jugs have a high SA:V ratio, being a curvy semi-rectangle with a hollow handle. A 1% surface area reduction results in a >5% drop in volume, about 7 fluid ounces per 1%, or 0.875 cups. Manufacturers really only see <1% reductions, but if they stuck with the same mold through the summer, they’d end up with a jug that looks to be about 0.5-0.75 cups low after filling. That’s pretty conspicuous for customers, especially since the top portion tapers, making the level drop even more dramatic.
I’m sorry, I’m just not buying this explanation. I’d need more evidence.
What surface area? It’s volume we’re talking about. You mean if the plastic gets thicker, thereby reducing the interior surface area there is a corresponding decrease in volume? And it’s 5 to 1 ratio? So if the plastic is thicker by 20% there is no room for milk?
Winter bottles, summer bottles? Like the temperatures aren’t controlled because it costs money? They just compensate with a plug, what every season? Like it costs money to control the temperature of a process but it doesn’t cost money wasting plastic.
Hey, I’m not an expert on this subject and I could be wrong but from my perspective you’re just some guy on the Internet that sounds like he knows what he’s talking about.
You’re welcome and encouraged to look into it yourself. You misunderstand what I’m saying and draw further conclusions based on that, though, so I can see why it doesn’t make sense. I’ll take a stab at explaining.
I did mean surface area, not thickness. As volume decreases, so do the dimensions of the object. The thickness of the plastic is already negligible and any change within that plane is a fraction of that, so even less pertinent here. The remaining two planes of the exterior, being several orders of magnitude larger, do experience functionally significant, easily measured change. Those two planes as they relate to volume are most succinctly explained as surface area.
I mentioned the SA:V change to illustrate that this size change isn’t visually apparent, so it’s important to adjust the volume via the dimple. This maintains a steady milk level so jugs can hold an entire gallon in the winter and ensures customers don’t think jugs are underfilled in the summer. In cold weather, the dimensions of the jugs reduce less than 1%, which means visually the change is difficult to notice, but the volume changes a fair amount, around 5%. A change in size imperceptible to most reduces the volume of the jug by about 1/20 without compensation*. By reducing the size of the dimple, less plastic can be used, which saves money.
- This is how manufacturers can so easily fly under the radar with shrinkflation. It’s hard to see, especially since they use shapes that obfuscate these changes, but they’re easy to calculate.
I actually think they’re correct. It explains most of it and jives with my experience.
The amount of plastic used is fixed. Here is a bottle blank I have for a 2 or 3 liter soft drink:
We’re assuming that milk jugs are blow molded from a similar blank at the bottling plant just before washing and filling.
Milk bottles are either High or Low Density Polyethylene. A notoriously elastic plastic. It also creeps all over with temperature, you can take a bowed 3" thick sheet of it, put it on the floor and it will usually be flat in the morning, especially if it’s above 75deg F or so.
Milk jugs aren’t a pressure vessel like soft drink bottles.
They’re saying that due to the large surface to volume ratio and thin walls, there is a lot of seasonal variation in final volume. This is primarily due to the compressed air used during blow mold, ain’t nobody paying to heat or cool it. Also, the ambient temps in the plant, in the blow mold area may see 40deg F swing, maybe more, over the course of a year. They aren’t going to pay to condition the air if it doesn’t affect final product. Fuck worker comfort.
This would be enough to show seasonal variation in milk level due to volume changes, especially since the jug necks up and exaggerates differences. Reduced headspace probably also keeps it fresh longer due to reduced oxygen. Mostly, if your competetior’s jug looks more full, you sell less milk. One producer does it, they all have to do it.
It’s a totally believable and logical explanation to me.
I agree with this guy, and I have to say it… username checks out.
I agree with you.
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
This also describes hiding shrinkage.
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.
You are correct that there is a connection to ensuring fill levels, but incorrect on it not being intended to provide structural integrity. It is both.
You can disable javascript to get around snopes adblock block: https://www.snopes.com/news/2023/01/07/milk-jug-indentations/
You can also view the original patent here: https://patents.google.com/patent/WO1999022994A1/en
Notable excerpt from patent:
When the horizontal ribs are not provided completely around the container, the face panels may be provided with indentions of preferably a circular configuration. The size and depth of the indentations may be varied to control fill level of a given volume of contents in the container in addition to further stabilizing the sidewalls.
I would not know our milk comes in tetrapaks.
And liters
Mine comes in bags.
Watching Glenn and Friends, I always marvel at this innovation. Wondering why we in America bother with so much package waste when milk can just come in a bag.
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?
Further south
The way the old Norse gods intended it to!
It would be the slavic gods in my case. Svarun be praised
I always believed that it was to allow for expansion of the product when it freezes. I often freeze similar jugs full of water, to use in coolers, and that big dimple always ends up pushed out after it’s frozen solid. If it hadn’t been for that expansion dimple, the jug would have split.
Milk is ruined if it is frozen.
I hate milk, so I never drink it today, but as a kid, I drank a lot of thawed milk. My mom always bought two gallons, and froze one while we used the first. It might not please a milk connoisseur, but it always tasted fine. It certainly wasn’t spoiled, or anything like that.
It causes the fat to separate. Maybe she got skim milk?
1-2%, so I never noticed any separation. I always shook up the milk whenever I used it on my cereal anyway. Probably still would, if I ever was to use milk for something.
I sometimes did the same, but I grew up on a dairy farm and had milk that wasn’t homogenized.
We used these old one gal apple juice bottles that had a narrow neck, so the cream would float to the top and collect in the narrow opening.
When I got older, I actually liked getting that first dollop of cream on my cereal.
Now though, anything over 2% just tastes too heavy. Growing up on unpasteurized milk, I am amazed at what I got away with.
I don’t mean to be rude, op, but I just straight up don’t believe you. This just doesn’t make sense.
Footnote: take memes seriously and get into fights with internet strangers
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.
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.
DISCLAIMER: I am not a milk jug engineer, that’s just how I interpreted it.
It’s added after molding the jugs and the volume is checked, but before the milk is filled.
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.
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
Only the mold is being adjusted, not each individual plastic jug.
These aren’t dimples, it’s the belly button. The umbilical cord was once attached to the jug at this point, after a few months of healing this is what the plastic scar tissue looks like.
The other end of the umbilical cord goes straight to the cow. After it’s cut, thats how you get cow udders!
If you jerk them the wrong way, 14 year old boys will giggle.
You buy milk in gallon-sized hard plastic containers?
Is that a restaurant thing? How long does a gallon of milk last in your family?
It’s a US thing. A gallon of milk will last my family about two weeks, or less if the kids are into baking or breakfast cereal that week. I sometimes put a little milk in my coffee or tea, and I occasionally use some for making sauces or marinades. Very rarely will we throw away milk because it has spoiled, but it has happened. Maybe once a year or so, usually because of a power outage or having to travel unexpectedly.
We also have half-gallon plastic jugs which feature the same dent sometimes. When I was a kid, I remember we even had tiny pint-sized jugs for half and half, but I think that was more of a novelty.
Wait…the rest of the world doesn’t have hard jug gallons? What do they use instead?
Just to add, in Brazil we usually have 1l cartoons of UHT milk or 1l bags of pasteurized milk.
Pasteurized milk goes bad in 3 days or so, and many people can’t run through the entire 1l in that time. UHT milk will last for a good 2 weeks after opened, so I guess that’s the kind you buy.
1l cartons
Bags
I miss bag milk. :(
So jealous.
That…looks so messy! I know there’s no crying over spilled milk, but have you SEEN the price of dairy??? Gotta work a second job just to afford breakfast!
How much does milk cost where you live? Maybe it’s just because I live close to the source but milk is around $3 a gallon for me. For another data point eggs are around $2 a dozen, often on sale for $1 (current exchange rates are around 1:1 for dollars to euros for those in euroland)
You put em bags into a hard pitcher thing you have at home, and cut the corner. So I guess it’s a bit less waste
That guy REALLY should have put an explanation there. Afaik there’s one province in Canada that still uses bags. Historically (30 years ago) many countries have used bags. Today most use either tetrapak, smaller bottle style plastic (0.25, 0.5, 1.0 litres) or actual bottles.
Isn’t that an Atlantic Canada thing? I know Quebec has them, and I’m pretty sure we weren’t the only ones in Canada with bagged milk.
Square space efficient packaging that you can finish within spoiling time, allowing for fresher products without additives. Easier to pour, packaging easily collapses for easier disposal. Fully printable and recyclable. A superior packaging in every single way.
In Sweden we use 1 to 1,5L cartons.
Futuristic technologies such as these
What accursed alien unholy wizardry is this burn my eyes burn my eyes
When I grew up here in Sweden, milk came in these containers:
https://en.wikipedia.org/wiki/Tetra_Brik
The design of milk packaging is quite interesting;
https://kommerduihag.se/kommer-du-ihag-hur-mjolkpaket-sag-ut-forr/
15 years or so ago the Brik was changed to this:
https://www.arla.se/artiklar/var-vanligaste-forpackning/
It was apparently done for two reasons:
- EU regulations started requiring that milk packages were sold in resealable containers.
- Customers had requested the same to enable storing the packages lying down.
A smaller version of the tetrahedron style package is still in use for coffee milk.
In Canada, they use gallon sized plastic bags
I’ve lived in various provinces in Canada. West of Ontario I really only see the waxed-paper cartons or the plastic jugs, stores carry both equally. Eastern Canada carries the plastic bags (and everyone has a plastic container at home they place them in after snipping the bag corner) and often the cartons. Bit weird the custom changes across Canada, and coming from the west I was very confused about the bagged milk when I first moved to Ontario.
Maybe someone else can comment on their experiences. I’ve never seen bagged milk in a store in the prairies (but I only lived in major cities).
They had milk in 1.3 L bags (sold in packs of 3 for 4 L) in Manitoba about 35 or 40 years ago.
Tbh, I haven’t seen bagged milk for quite a while where I live in Canada. It’s typically cartons for 2L or less (though sometimes mini plastic jugs too) and plastic jugs as in OP for 4L.
Still very much a thing in Eastern Canada.
Interesting how it varies across the country.
Well, a bag holding 3 x 1.3L bags.
Here in Australia we have:
1L Jug
2L Jug
3L Jug
1L Tetra Packs (Less common, more often for UHT milk)
1L Hard Plastic Bottle (Less common, more often for high priced ‘fancy’ milk/plant milks)In the U.S. milk comes in half gallon and gallon measures, which look like your 2L and 3L containers, respectively.
Sometimes you will find milk in waxed paper cartons, but that is not the norm. (It’s very common, however, for dairy products that are often bought by pint and quart — typically half and half, heavy cream, or coffee creamers.) Our fancier non-dairy creamers tend to be in tetrapaks or cartons, with less expensive (or at least distributed in higher volumes) creamers in plastic bottles.
One liter (0.26 gl) bottles or boxes.
Bags I think.
I would never drink a milk that lasts two weeks. Real food spoils. This must be some liquid plastic.
Two weeks is an ordinary time for refrigerated pasteurized milk. If you’re used to a shorter timespan, either your milk is unpasteurized, inadequately refrigerated, or you’re at the end of an inefficient distribution chain.
Option number 4. The sanitary standards for packaging milk are very high in North America. This drastically reduces the risk of contamination after pasteurization, which allows our milk to last quite a while. It isn’t as sterile as UHT milk, but it tastes more natural.
The sanitary standards for packaging milk are very high in North America.
Well, perhaps used to be. Now the oversight on those kinds of things is gone, and companies can do whatever pleases them. I wouldn’t put my trust in their good faith at all.
Well, I’m in Canada, so the standards are already higher as far as quality goes, and our regulatory agency is still in place for oversight. I’d say it’s worth it for them to keep the quality up so product lasts longer, but I’m sure some bean counter will figure out a reason for how allowing the milk to spoil sooner makes the company a buck, so we’ll see.
The proof is sort of in the lifespan of the milk.
I haven’t noticed it going bad sooner yet. It’s possible that other adulterants start showing up, but there are still lawyers that can sue companies if they find them fucking around.
That said we need to kick the fucker who are enabling this shit, out of the government ASAP.
Fresh milk that’s been pasteurized and refrigerated should last at least three weeks.
the container isnt very hard, it’s pretty thin but I’ve never had one break. It’s sold at grocery stores in the US (idk about others) and have only ever seen this kind or the cardboard kind.
Here’s an image that’s essentially what the milk section at my local Walmart looks like:
It really depends how long it will last because sometimes my family will go through two a week and other times it’ll stay there for a couple weeks before being thrown out. In general I’d say about one gallon a week for 5 people.
What kind of container does milk come in from where you live?
I can confirm they do actually break quite easily… uh, from experience. They don’t shatter, at least, you just end up with very leaky milk and a grocery store worker disappointed in you.
It may not be hard, but man do I work it.
Jokes aside yeah I reuse my milk jugs to refill with tap water… And forget to replace it with a new one. So I use a milk jug for water for about a year, then remember to swap it out. So it is pretty structurally sound. (Though it may be leaking chemicals into my water … idk)
A weeks worth of cereal, and used as ingredients usually.
It’s more normal to us than bagged milk
I have a family of four and we live in the Midwest in the United States; Minnesota to be specific. We will go through 5 gallons of milk in weeks time between cooking and drinking.
Pretty sure it’s mostly an American thing, but I’m not well-travelled enough to be sure.
And as for rate of consumption… When I was a kid, my parents made me drink a glass of milk every day - call that 8oz, so 56oz per week. That’s a little under a half gallon (which you can also buy in plastic jugs), not including other uses like tea/coffee and cereal. Altogether, we’d go through about a gallon per week.
I bought them as the sole drinker.
How long does a gallon of milk last in your family?
Months if you just mean how long it’s in the fridge.
I can do a gallon of milk in two or three days
Very fascinating, so much so that i don’t think it belongs in lemmy shitpost
