This Is What Those Circles On Milk Jugs Are Actually For

There are many mysteries in this world that keep us wondering. We can't help but ask ourselves: Where is Cleopatra buried? Who is making those crop circles? What kind of cheese really is the best for a grilled cheese sandwich? And what are those inverted circles on the side of our milk jugs for? These are things that keep us up at night. Pretty heavy, right? So imagine our shock and surprise when we learned one of those musings actually has an answer.

If you don't know what we are talking about, check out a typical plastic gallon or half-gallon milk container in a grocery store in the United States and you will notice a round inverted circle. Well, it turns out they have a real purpose. Distractify was one of the first to try and tackle this question, revealing those circles play an important role in the way the milk jug has been structurally engineered. And that much is true, but the site goes on to explain the circle also plays a role in helping milk lovers know when their milk has spoiled and soured. This is where USA Today's sleuthing comes into play.

It's about how full the milk jug appears

USA Today did some fact-checking and as it turns out the inverted circle does have a purpose, but it has nothing to do with milk spoilage with the article noting that bacteria can ruin your milk beyond drinking without creating any gas.

So what are those indents for? USA Today goes on to explain they spoke to Matt Herrick, senior vice president of communications at the International Dairy Foods Association, who shared that those inverted circles allow for control over volume and weight. 

Because the material the jugs are made from tend to shrink with heat or cold, but more so with the heat, the makers of the jugs have to change their size to account for this. Without interchangeable volume inserts (the circular indents), the jug could spill over or, worse, look like it doesn't have enough milk in it. Why this matters: because as Mike McCarty, vice president and sales manager of plastic bottle manufacturer Indiana Bottle Co. told USA Today, "People who buy milk jugs, they want them to be full."

No one wants to buy a gallon of milk that is not completely full, so now you know.