Milk Froth - Beer Froth

Who hasn’t been annoyed by flowing or frothing over milk? The question arises, why this doesn’t happen when cooking water or tea? In general, the ingredients of milk are responsible, which behave differently when heated.

By the way, milk is not a beverage, but a food. It contains all the essential nutrients and ingredients for the constitution of the body: carbohydrates, proteins, fats and minerals.

So what happens when milk is heated (frothed)?

1. Below 80°C: The milk fat (yellow) floats in the milk because of the enveloping protein layer (blue).
2. Above 80 °C: the protein layer (casein) is destroyed. Since the protective wrap of the milk fat is now missing, the lightweight fat floats to the surface and fat droplets are formed, which can be seen when the milk is slowly heated. The casein floats to the surface as well, links together and forms a skin. The layer of fat and the skin work like a lid (insulator) and the heat of the cooking top can’t escape via the milk surface like in cooking water.
3. Heat congestion occurs. The vapour bubbles rise from the bottom of the pot and lift the skin. Milk forth is generated (grey).
4. The froth is not very permeable for the heat either and thus more vapour bubbles are generated at the bottom. They rise to the surface and lift the froth further. The mountain of froth increases and eventually the milk flows over.

Why does only beer froth when it is poured out?

The reason already lies in the creation of the alcohol: During fermentation, the yeast converts the malt sugar into alcohol and carbon dioxide. The gaseous carbon dioxide now floats in the beer invisibly. When the beer is opened or poured out, the carbon dioxide escapes (sparkling bubbles are visible in the beer) and creates beer froth as a result.

Why does the carbon dioxide escape from the beer?

• On the one hand, the counter pressure, which has been built up in the bottle (keg) ceases as soon as the beer is opened.
• And on the other hand, the beer hits the glass walls when poured. The more intensely it is poured, the more it froths. So when you pour the beer slowly and tilt the glass, little froth is created.

The temperature, too, influences the frothing of the beer: The warmer it is, the faster the carbon dioxide escapes from the beer and it starts to froth. Cold beer froths less. The ideal temperature is around 8 °C. Well, cheers then!