Why does beer have foam?It's not just carbon dioxide

One is to understand that the basic principle of foam formation is that bubbles are formed under the action of gas due to the different surface tension of different components in the liquid.When a liquid with high surface tension encounters a gas, the film formed will not easily break. The gas is wrapped in the film, and the appearance is foam.Generally speaking, the surface tension of oleophilic substances (such as the vegetable oil we eat, etc.) is small, and it is not easy to bubble when encountering gas.And because beer contains peptides (that is, medium-molecular proteins), the surface tension of beer is relatively large, and it is easy to bubble when encountering gas. If you touch the beer foam with an oily substance, the foam will disappear immediately, mainly because the oily substance reduces the surface tension of the beer.

The second is that the beer contains CO2 gas. Before the lid is opened, there is pressure in the beer bottle. As soon as the lid is opened, the pressure drops. The CO2 gas that was originally dissolved in the beer is immediately released from the inside of the beer and escapes from the outlet with low pressure. In this way, a large amount of foam will appear in beer with high surface tension.

Most of the gas in beer is carbon dioxide produced by yeast after metabolizing sugar into alcohol under anaerobic respiration in home-brewed beer equipment, and the carbon dioxide is then dissolved in water.

Carbon dioxide in beer is generally produced in two ways: one is produced by yeast in the secondary fermentation of the bottle. This is the case for most craft beer, so there are live bacteria in it; industrial mass-produced beer generally requires high-temperature sterilization and disinfection. After the fermentation is completed, food-grade carbon dioxide needs to be injected before bottling after disinfection, or carbon dioxide produced by the fermentation process originally collected.

Some beer will add nitrogen to it. Its role is to make the beer easier to drink and smoother, enriching the taste, but the solubility is very low.The solubility of nitrogen is only 0.024, so for general nitrogen beer, a nitrogen ball must be added to the jar, and it will not be released until it is drunk to avoid excessive air pressure in the bottle.

The durability of foam is also an important indicator for evaluating beer

Beer foam must be formed mainly by gas, so it is mainly carbon dioxide, but gas alone is not enough, and substances are needed to maintain the shape of the foam. For example, soap bubbles must rely on soap ingredients to maintain.As long as beer has gas, it is no different from soda/Coke, and it will disappear in an instant.

Scientists have done experiments: use nitrogen to blow up beer foams, collect these foams for analysis, and find that the remaining solid components are mainly carbohydrates. Among them, the most important thing related to the foam is protein, which is needed to make the beer foam last. Protein.