Why a down-the-side trickle?

Here’s what I mean: I open up a carton of milk, intending to pour some into my coffee. I tilt the carton, expecting gravity to carry the liquid straight into my coffee, situated directly underneath the spout. Instead, the milk curls around to slide down the outside surface of the carton! Why? What’s the physics behind this phenomenon? What’s the trick to avoiding it?

I’m going to venture a guess, just because I like getting my butt whupped by the phis . . . er, fizz . . . um, science guys, and say “surface tension.” The tendency of water and other liquids to cohere and form a tight surface, combined with tiny irregularities in the surface of the carton, mean that it requires less energy to go over the lip and down the side than to break with the surface and pour straight into your cup.

Close enough IMHO

Actually, “trickle-down-the-side” is due to Reaganomics.

And the solution is to pour faster. This gives the liquid enough energy to easily break off of the surface. Also, if you tip the container far enough that the outer surface slopes upward, not down, you won’t get any trickle, although this might not be practical for a nearly-full carton.

Right. It’s not very practical for milk, but I can tell ya it’s fantastic for beer.

Uhm…what kind of cheap beer do you buy? I’ve never even seen beer in cartons!
ok, ok…sorry.


Buy yourself a nice porcelain cream pitcher. You’d still have to deal with the drag-pour once, when you fill the pitcher, but then the vessel elegantly fulfills it’s purpose. My favorite is shaped like a cow, and the cream comes out of her mouth in a nice even stream. Especially fun if you go "MMMMOOOOOOOOO"as you pour. (I’m all too easily amused in the morning.)

Another thought: Is the carton torn open evenly? If you had a struggle with it, sometimes the cardboard frays, making the cream hang up and therefore a messy pour.