[ELI5] Why do bubbles form when you blow through a straw into milk?



I’ve always wondered since I was a kid why it does this.

[This image is representative of what I’m talking about](https://i.pinimg.com/474x/66/68/d6/6668d6e7d6cc10177eb2196c84a822d6–sweet-tea-making-memories.jpg)

In: Chemistry

Just like any other liquid you pushing air into it causes the oxygen to rise. Due to the surface tension of liquids, eg water, which is less dense than milk, the air rises and escapes to the top. But since milk is thicker(heavier/denser) water the bubbles hold on longer and tighter and you get that furious lifting of bubbles.

I’m sorry I can’t explain like I’m five. Does anybody else have a better explanation

This happens with anyliquid. You put air in it the bubbles will rise to the surface and usually pop, but milk has a lot of other additives besides water that makes it thicker so the air has trouble rising to the surface

Others have mentioned the milk’s thickness, but that’s only part of the equation. Milk has proteins in it. Those proteins are like really long, really sticky chains. The ends of the chains are really good at grabbing onto each other like Velcro, because they’re meant to hold things (like cells) together. This means that when you blow bubbles into the milk, those proteins at the surface will try to hold onto each other, and as the air pushes upwards they will stretch out or flex instead of simply breaking. When the air reaches the surface, it has a thin membrane of fluid and proteins holding onto each other. This forms a bubble.

This is also why pee can be foamy. Excess foam is an indicator that your kidneys may be filtering out lots of proteins. Maybe because you simply have a high protein diet and your body doesn’t need all of the proteins it has, or maybe you have some sort of kidney issue.