The bottom of the fermenter will have three layers of yeast
The top layer is light yeast, including impurities such as frothing caps, yeast sediment, some proteins and hop resin sediment. It can be used as feed and other integrated uses.
The middle layer is the core yeast, which is a combination of strong, healthy and highly fermentable yeasts. Its percentage is about 65-70%. This fraction should be recovered and used for the next fermentation batch. The color is light.
The bottom layer is dead and weak cells with many impurities, so it can be used as feed or just thrown away.