How the CO2 and foam of beer are formed
How the CO2 and foam of beer are formed?
Beer has four basic material: Malt, water, yeast and hops.
The simple process for beer is as below:
Yeast live in the water and his dinner is the sugar in the malt. He digest sugar and produce the alcohol, othersecondary metabolites and CO2. Then they combined beer by adding hops.
This is too simple and a little disgusting? Okay, let’s discuss beer from science.
Most CO2 in beer are produced by anaerobic respiration of yeast. The CO2 solubility of beer range between 1-3 for different kinds beer. 1 is the normal degree that CO2 in water.
For example, the CO2 solubility in the original Lambic is 1, so original Lambic has no bubble.
The imperial stout also have a lower CO2 solubility while the Belgian monastery beer and Germany wheat beer have a higher CO2 solubility, 3 or more level.
Other CO2 in beer comes from secondary fermentation in bottle or carbonation before bottling.
2. Foam in beer
Normally we calculate the foam retention of beer by the time that foam reduce from full foam to half. CO2 is the main composition of beer foam. But beer foam also included other components like carbohydrate. While the protein is the main carbohydrate.
There are two main proteins, Long chain high molecule protein and Short small molecule protein.
Long chain high molecule protein takes 10% protein, it is mainly composed by the hot break protein. This kind protein play a critical role in foam retention.
Short small molecule protein is mainly composed by Lipid transport protein, the alcohol-soluble protein of barley and glutelin. They play an important role in foam formation.
So both two kinds of proteins are important to foam retention. The wheat beer has a better foam because of wheat rich in protein.
Edit by Miya Zhao