Oversteeping tea refers to the process of leaving the tea leaves in hot water for an extended period beyond the recommended steeping time. When tea is oversteeped, it can result in a stronger, more bitter, or astringent flavor profile. The specific consequences of oversteeping can vary depending on the type of tea being brewed.
Delicate teas are susceptible to becoming bitter when oversteeped. The longer the tea leaves remain in hot water, the more certain compounds, such as tannins, are extracted, leading to a potentially unpleasant taste, becoming too strong and making the flavor undrinkable in some cases. Oversteeping tea can lead to ncreased likeliness of reacting if you're sensitive to tannins. More on that here!