Does My Milk Jug Really Tell Me When Milk Is Spoiled?

Southeast Dairy Association - milk

A seemingly educational post made its rounds on social media earlier this year claiming that the design of the milk jug signals when milk is fresh and when it is spoiled. According to the post, the circle on the milk pops out when it’s old. 

The explanation is that gas produced by the bacteria in milk builds up in the space, eventually forcing the indent to pop out once the milk is too far gone to drink. 

Though we at The Dairy Alliance don’t consume milk slow enough to worry about spoilage, that sounds like a cool invention. It’s always a sad moment when you discover milk has gone bad. Maybe you were stretching it until your next grocery run for a favorite recipe or the weekend bowl of cereal, just a little longer than you would normally wait to enjoy delicious milk. Or maybe you completely forgot about that other half-empty jug. Your hopes are finally dashed when the moment comes for whatever you have been looking forward to and you twist off the cap. For those that don’t have another gallon to move on to, it’s a moment you wish you saw coming. 

And while such an invention would be helpful in a world of confusing dates on food packaging, the indent wouldn’t pop out because the milk’s age is just a little too old. 

milk with orange slices and cookies

So why does a gallon of milk have a circular indent on two sides of the container? It isn’t just a style decision. The indent helps control the amount of milk filled and strengthens the jug enough to hold the nutritious milk inside.  

Unlike heavy and breakable glass options, lightweight plastic jugs  

They also (slightly) change size according to the surrounding temperature. The jugs are made slightly larger than needed in case of shrinkage from the summer heat, which would make the milk overflow. Other times, they are made slightly smaller in colder months so they don’t look underfilled. The indentations make that change easier, all while bringing consumers the same amount of milk all year long.   

And though the jug doesn’t tell you when to toss the last of your milk, there are ways to slow down spoilage and put off the sniff test. One way to slow down spoilage is to keep the milk cold for as long as possible. Grab the milk towards the end of your grocery run. Once home, place the jug in the back of the refrigerator, not the convenient shelf in the door. The back of the fridge is colder and isn’t as impacted as food in the front when the door is opened for those midnight snack considerations. 

And the easiest way to keep milk from spoiling? Don’t keep it just for the baking. Enjoy your three servings of milk a day.