16 August 2019
About those dimples on the sides of milk jugs - updated
I had never paid attention to these dimples before; if I had I would have assumed they were to facilitate gripping the jug, but they are on the wrong side and seemingly superfluous for that purpose when a handle is present on the other side.
I have seen claims that these are pressure relief valves that pop out if the jug is dropped or the milk spoils and produces gases or freezes, or that they are structural supports for an otherwise smooth wall, or that they allow the size of the container to be varied without changing the mold,
As soon as this jug is empty I'm going to test the pressure-relief theory by dropping a water-filled one and/or freezing it.
It worked - sorta. When the jug was empty I refilled it with water, adjusting the level to match the new unopened jug (airspace about 5cc under the cap). I then tightened the cap and took the jug to the driveway, where I dropped it from waist level to simulate a shopper's misadventure...
Both dimples popped, one of them blowing out completely. I'll plan to try once more, next time dropping from a lower height.