Buzz
No matter if you’re buying whole, 2%, or skim milk, all plastic milk jugs share a key feature: an inward curve on one side where you'd usually find a flat surface. If you drink milk, you’ve probably noticed this, but the clever reasoning behind this design may not be immediately clear.
As stated by Distractify, the concave shape on the side of a milk jug enhances its structural strength. A gallon of milk with flat sides might be stable in your fridge, but drop it, and it would likely break. The dimple helps prevent this by flexing outward when the jug hits the floor, providing a space for the milk to shift as it expands. This added flexibility makes the jug more durable.
This feature also proves useful as milk nears its expiration date. As harmless microbes in the milk release gases, the jug's internal pressure rises. The flexible dimple helps prevent the jug from bursting. A more extreme example is when you freeze milk. Liquids expand when frozen—just like how a can or bottle of soda can burst in the freezer. But with the inverted circle, milk can be placed directly in the freezer without the risk of spilling or breaking the container.
In the United States, the dimpled milk jug is a familiar sight, but it's not the sole method of safeguarding milk. In Canada, plastic milk bags offer a more durable alternative to glass jugs, largely due to the adoption of the metric system.
