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.
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.
We had those in Vancouver, too, which came from a dairy in the Greater Vancouver Area. I used to get fancy milk on payday and keep the bottles for crafts, away from the recycling bandits. They love them because you can get like a dollar back, per each.
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.
We have one particular brand here that does “Milk, ice cream & more” that has their milk in glass bottles. It’s this ridiculous super premium thick milk, I get some of the chocolate sometimes.
I think it’s about $6per (half gallon/4pint) which is considerably more than average but it’s like drinking chocolate ice cream.