In actual production, there are two main categories of yeast for the most commonly used beer brewing equipment in mini brewery: surface yeast and bottom yeast. There are obvious differences between the two forms.
Bottom yeast is also called stored yeast. Their mother cells and daughter cells will be separated after the proliferation, almost all are single cells or several cell connections.
Surface yeast is also called top yeast. Its mother cells and daughter cells can be connected to each other for a long time, can form 5 to 10 branches of buds. The carbon dioxide bubbles produced during the fermentation are surrounded by buds, the yeast are attracted to carbon dioxide bubbles, resulting in the formation of aggregates of yeast and carbon dioxide bubbles, the density of the pellets is less than that of the fermentation broth, so floating on the liquid surface.
Of course, the nature of surface yeast and bottom yeast is not static, and sometimes change.