Michael Plant, who has enriched this group with a diversity of wit, wisdom and actual useful information that would do credit to Dr. Johnson, has admitted to employing a twist on the usual metronomic or monotonically lengthening interval between gong-fu steeps. Viz.: he'll do a pot the usual way, immediately take a second extraction, then let the pot rest until both cups have been consumed. Or something like that; he can explain better.
While discovering aberrant behavior at this locus is not in itself surprising, the merits of this technique might be. First, allow me to assert a few presuppositions, unproven by "Science" AFAIK:
- Many people seem to imagine tea brewing as though a pill or bolus of matter were smoothly dissolving. This is definitely not the case. Even the refinement of considering some goop smeared into the pores of a sponge doesn't quite make it.
- While dry leaf may equilibrate thermally in a second or two, full hydration probably takes closer to a minute.
- Substances are extracted from the leaf by multiple mechanisms on multiple length scales, from direct displacement off polymer surfaces and out of interstices, to diffusion and percolation through pores in the leaf structure, to gross convective mixing in the bulk.
- The rate of these processes depends intimately on the local environment. This means hydration on the nano- and micro-scales, and mechanical separation at the leaf-in-water level. It also means that relative extraction rates of diverse substances may be very different in the first few steeps, before the "dilute solution" approximation applies - especially within leaf pores and in the polymer matrix.
- So instead of (1), a more accurate representation might be similar to the "coupled compartment" model used in dive computers to estimate tissue nitrogen loading, further modified to accommodate Case 1 and Case 2 diffusion (ie., diffusion that is linear or history-dependent) as hydration is achieved, and non-linearities early on due to the concentration of extractables that themselves affect solvent properties.
I know, that was all obvious. Here's the fun part: I've actually done a few dozen crude experiments with Michael's approach, and confirmed that once the leaf is fully hydrated (usually after one or two steeps), extraction continues at about the same rate whether the pot is full or "empty." This is not surprising: once the rate of extraction has declined to the point that there is little solvent change due to solutes, there is more than enough water in and on the leaf to "carry" what's coming out of those notional compartments. There just lacks any bulk fluid to carry it away. Since the pot innards stay hot, the intersteep hiatus is actually "stewing" those valuable leaves.
Michael's method helps a lot, and is instructive as regards change in flavor balance (as distinct from overall intensity) with oversteeping. What I found works even better, though I can rarely be bothered, is to make that fast second steep with much cooler water, just at comfortable drinking temperature. This washes off the ready-to-go goodies, and leaves the leaves in a calm mood to await a new poaching after I've consumed both cups. Makes a more uniform series of steeps. It also means that in addition to the 300 pots that Michael has demonstrated are necessary for any serious tea drinker, you will also need a second Zojirushi.
-DM