Books and articles sometimes put it like this. Hojicha is not astringent because the heat of roasting destroys the compounds that make astringency. One sentence settles it, and the reader is satisfied. It is worth standing in front of that sentence with the figures gathered so far.
How much of the account of “not astringent” is measurement?
As far as the swap. No study found here tests whether the new forms are astringent at the strength of a hojicha infusion.
At tea strength, the four epi-type forms are the ones tasted
At the concentrations found in tea infusions, the compounds tasted were the four epi-type ones. On the rising side, a 1999 study had eighteen trained judges rate the bitterness and astringency of catechin (C) over time, but it was not a study of tea. No study found here tests the four rising compounds at the strength and under the conditions of a hojicha infusion. On top of which the 2022 review states that much about how astringency is received remains unclear, and that the sensation is held to be a mixed one, of bitterness and physical stimulation. The sensation itself is still finding its footing.