Tofu marinated for hours often tastes of nothing beyond its surface. The reason is that its interior is already full, and marinade cannot occupy space that water is holding.
Tofu is a gel, not a sponge
Soy milk is set with a coagulant, which links its proteins into a network that traps water throughout the block in the same way a set custard does.
That water is held within a fine structure rather than sitting in open channels, so liquid poured over the outside has nowhere obvious to travel.
Marinade therefore coats the surface and penetrates a millimetre or two, which is why a cube can taste strongly seasoned at the edge and bland in the middle.
Pressing opens the structure mechanically
Weighting a block drives out a portion of the loosely held water and slightly compacts the protein network, leaving the interior less saturated than before.
The result absorbs seasoning further in and, more importantly, browns properly, because surface moisture no longer has to boil away before the pan can brown anything.
Firmness on the label indicates how much water was pressed out during manufacture, which is why firm varieties need less work and silken varieties cannot be pressed at all.
Freezing changes it more than pressing does
Water expands as it freezes, and the ice crystals push the protein network aside, leaving voids behind when the block is thawed and squeezed.
What comes out is visibly different: spongier, chewier and full of open spaces that draw liquid in rather than resisting it.
The trade-off is that the smooth texture is gone permanently, so the technique suits braises and stir-fries rather than dishes where delicacy is the point.
Heat does the same job from the outside
Frying or roasting drives water out of the outer layer and sets a firm skin, which then takes on sauce readily while the interior stays soft.
This is the logic behind cooking tofu first and saucing it afterwards, rather than marinating it raw and hoping the flavour travels inward.
Coating the dried surface with starch before frying exaggerates the effect, giving a crust that grips sauce instead of shedding it.
Salt is the exception that travels
Salt dissolves and moves through water, so brining does season a block throughout in a way an oil-based marinade never will.
That is why simmering tofu in seasoned stock, or salting it well before cooking, changes the interior when a surface marinade does not.
Everything else worth tasting is too large a molecule to make that journey, so it has to be delivered to a surface that is ready to receive it.