Strainers are an integral component of the tea brewing process. Tea strainers or tea infusers are for the fundamental purpose of straining out the tea leaves from the tea.
When you prepare tea using tea leaves, it's difficult to avoid staining the tea strainer ball or tea strainer cup. The strainers become tea-stained over time and dirty-looking. Of course, the intensity of the tea stain largely depends on how frequently you use the strainer to brew tea.