The content of flavanols, including EGCg, in a cup of tea varies
remarkably. It depends on steeping time and temperature. For
the extremes examined here (3 min at 70 C and 7 min at
100 C), the concentration of EGCg is 3.1-fold higher in the infusion
prepared at the higher temperature and for the longer time. The
factors for the other flavanols are similar. Further, lowering pH of
the infusion increases the concentration of flavanols. An increase
of 20% (EGCg) is found for pH 3.0, which is the pH of a cup of tea
with 10 mL of lemon juice.
Two reaction mechanisms are proposed, that are inversely affected
by steeping time and temperature: the diffusion of flavanols
from the leaf into the aqueous phase and their structural alteration.