Compression is a storage decision with a brewing consequence
Tea is pressed for transport, for slow ageing, and for trade and taxation reasons that vary by region and by period. None of those purposes has anything to do with how the tea brews, and all of them affect it. A pressed cake presents water with a dense, layered mass whose interior is barely accessible: extraction begins at the outside and works inwards as the piece gradually loosens, which is why a compressed tea’s session climbs for several infusions where a loose tea’s peaks early. The person breaking the cake decides how much of that resistance survives into the pot, and that makes it the largest single variable in brewing compressed tea — larger than water temperature, larger than the schedule, and larger than the vessel. It is also the variable least often discussed, because it happens before the brewing is felt to have started. Two people brewing the same cake with the same numbers can produce quite different sessions purely on the strength of how they got the leaf out of it.
A pick separates; a knife cuts
The tool matters because the two actions produce physically different material. A tea pick or awl driven in along the plane of the cake and levered gently separates the pressed layers from one another, and the leaf comes away largely intact with its structure preserved. A knife, or a hard downward chop with anything, cuts through leaf rather than between it, producing broken edges and a quantity of fragments and dust. Intact leaf and broken leaf extract at different rates and give different balances, so the second approach does not merely portion the tea, it changes it — and it changes it in the direction of a faster, harsher, shorter session. The technique that follows is to work from the side rather than the face, follow the layers rather than fighting them, and lever rather than force, accepting that a properly pressed cake takes a few minutes and a moment’s care. It is also considerably safer, since the injuries associated with this task all come from forcing a blade towards a hand.
Chunk, flake and crumb are three different brews
A single thumb-sized chunk placed whole in a gaiwan gives a slow, late-peaking session that can run for a very long time, and it may still be dry in the middle after three infusions. The same weight separated into loose flakes gives a session much closer to a loose tea’s: a quicker peak, more early intensity, a shorter tail, and far less of the sense that the tea is still arriving. Crumb and dust extract almost immediately and dominate the first two infusions entirely, contributing colour and grip well ahead of anything else. Most drinkers want something between the first two, and the practical target is flakes with a little of the leaf still adhering to its neighbours, rather than either a solid lump or a pile of fragments. Which end of that range suits depends on the tea and the session: a long unhurried afternoon rewards the chunk, and a quick session before work rewards the flakes.
The uneven-extraction problem
A vessel containing one dense chunk and a scattering of fines is running two different extractions simultaneously, on the same schedule, and averaging them in the cup. The fines are finished by the second infusion and the chunk has barely started, so the early cups carry a disproportionate share of what broken material gives — usually more astringency and colour and less body — while the later ones are still climbing towards a peak the drinker may have stopped short of. This is the mechanism behind the very common complaint that a cake is harsh at the beginning and thin at the end, and it is a preparation fault rather than a fault in the tea. Sifting the dust out and brewing it separately, or keeping it and deliberately shortening the first two infusions to account for it, both address the problem honestly. Ignoring it does not, and it produces a session that seems to contradict itself.
Where to break it from
Cakes are generally pressed less densely at the outer edge and around the depression on the back, so entering there takes less force and does less damage than attacking the face directly. Working around the circumference and lifting a wedge is usually easier than trying to lever out a portion from the middle. The paper wrapper and the small printed ticket often pressed into the surface are worth keeping with the tea: they carry the only identification it has once the wrapper is off, and a broken cake in an unlabelled jar becomes anonymous within a year, which matters a great deal for anything being kept. Tuo, brick and the smaller pressed formats are typically compressed harder than cakes and give less at the edges, so they often have to be worked at from a corner. The very hard small pressings sometimes need to be broken rather than separated, and accepting the fines that result is more sensible than fighting them.
Breaking ahead of time, and what it costs
Prising a portion loose at every session is inconvenient, and breaking a whole cake at once and keeping the pieces in a jar is common and practical. It has a real cost that should be understood rather than discovered. The compression that slows brewing also slows ageing, because it limits how much of the leaf is in contact with air and moisture, so broken material ages faster and considerably less evenly, and loses its volatile aroma more quickly. For a tea being drunk over a few months this hardly matters and the convenience wins outright. For one being kept for years it matters a great deal, and the usual compromise is to break off a session’s worth at a time from a cake that is otherwise left intact and rewrapped, keeping the loose pieces in a small jar and the cake in its paper. That also preserves the option of selling or gifting it, since an intact cake and a jar of broken tea are not the same object to anyone else.