Everyone knows that caffeinated beverages will give you a small froth if you dump them in a glass. The Dutch apparently require a good a amount of froth in their beer. But at the same time Blue Gatorade has the same consistency as my pee, but my pee froths 10x as much when I shake a pee bottle. Why come?
In: Biology
Quite simply the gases used in the production or formed from reactions within the liquid. Different liquids have different gases that form and/or escape from the liquid. For example if you pour coca cola into a glass quickly the amount of carbon dioxide gas (CO2) will rush to the top of the coke due to the gas having a much lower density. Beer is very similar however there are slight differences to what make the ‘head’ of the beer. CO2 is the gas which rises to the top like in the coke however you also will get other compounds formed from the production processes which allow the suspension to remain for longer periods of time. These other compounds form usually from fermentation and/or forced CO2 when pouring. Coffee is similar. As the coffee beans are roasted CO2 and air can be trapped within the bean however once ground a lot of the CO2 escapes. Some of it remains and is forced into the hot water producing a slight gaseous foam as the rest of the CO2 escapes.
The amount of foam will represent the amount of CO2 within the liquid in the cases I’ve stated above.
Pee is a little different but similar in the sense that gas is less dense than water. When you shake pee in a bottle you are allowing air to mix with the liquid which forms bubbles. Also you are allowing the mixture of oxygen with specific proteins that may be present in your pee such as albumen. This then breaks up the protein, releases the gas and allows for a froth to sit above the liquid.
So caffeinated beverages in themself will not froth, necessarily. Coffee froths because it have proteins in it that form structures that trap air bubbles (look up coffee foam). Same goes for dairy milk in a latter. Almond milk has a lower amount of protein (or at least that kind that make structures) so it takes a skilled hand to make them froth.
Your pee will froth if it has tons of carbohydrates in them (which is a bad sign). Carbs are why you can make Gatorade frothy too. Carb structures are weaker than protein structures which is why they fizzle quicker and make less foam.
Beer has little bubbles of carbonation from the yeast eating and pooping out CO2, which collects into small bubbles. Beer has carbs but they aren’t typically whipped into structures, so it’ll go flat fairly quick.
Soda has bubbles added artificially. It stays bubbly because the bottle/can is pressurized.
Not mentioned yet is the presence of a surfactant (soap). This reduces surface tension and makes it easier for bubbles to form and remain. When combined with a blowing agent (carbonation), foam builds up.
Think of mixing soap and soda
[Foaming Agent](https://en.m.wikipedia.org/wiki/Foaming_agent)
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