Why You've Actually Been Pouring Milk Upside Down

Here's a quick question: how do you pour your milk? No, it's not rhetorical. You've likely never even thought about it. Pouring milk into a cereal bowl or glass really isn't rocket science, right?

Here's a related question: when you pour milk into a bowl of cereal or a cup of coffee, how many times has the milk bubbled up and splashed out onto the counter or, worse, ran down the side of the jug instead of straight out? When it comes to pouring milk, there are those who see it as more than just another step in preparing breakfast. Perfect Daily Grind, for example, details how the "art" of milk pouring is key to ensuring a good cappuccino. There are even those who even swear by pouring milk in the bowl before adding cereal (via ABC 7 News). It seems that, for some people, you're either pouring milk the "right way" or the "wrong way."

If there's a wrong way to pour milk, then what's the right way? Is there any real difference or is this just yet another insignificant thing that people on the Internet are fighting about? According to some, this simple pouring technique helps to eliminate any messes that you may make while pouring yourself a cup of coffee or bowl of cereal.

When you grab your carton of milk or juice in the morning, you probably hold the carton so that the little plastic spout is right over the cup or bowl. The reason for this is obvious: the liquid will come out of the spout and right into the container. But when you pour it, does the liquid ever pour weirdly? Instead of flowing smoothly, it comes out in spurts or glugs, splashing everywhere and making a mess. One trick supposedly eliminates this problem, and all it requires is for you to turn the carton.

Simply flip the carton so that the other side is facing the bowl or glass. Rather than have the plastic spout be closer to the bowl, you'll want it farther away. As you pour, the milk or juice inside the carton will flow out more freely, instead of in spurts or hiccups. YouTuber Amazing Stuff demonstrates that this method of pouring works– and is much cleaner too! 

But how does flipping your carton of milk or juice change how the liquid comes out? How can such a simple change make such a big difference? The answer lies in the pressurization of the carton's interior.

When you think of pressure in your drinks, you most likely think of the carbonation in soda or a bottle of champagne. If you shake either up, then quickly open it, the build-up of pressurization is what causes the resulting eruption of fizz. While milk isn't carbonated and won't explode if you shake it up, the air pressure inside the carton does still affect how it pours. The trick involves matching the internal pressure of the carton and the outside air, a process called equalization.

As Mental Floss explains, there's an air bubble located right at the top of the drink container around the spout. If you pour the way people typically do, with the spout directly above the glass, the pressure inside the carton attempts to equalize, but the liquid gets in the way. The air interrupts the liquid flowing out and gives you a bubbly pour. When you pour with the spout on top, the pressure inside equalizes without the liquid getting in the way because the liquid is less likely to completely cover the spout. You could technically turn the carton sideways and also get a similar effect, but this is harder to do with one hand.

Although this is a relatively minor hack, at least you don't have to go crying over spilled milk again.