Put a raw chicken breast and a can of chickpeas into the same pot, and heat does two different jobs. The chicken's proteins are clenching and turning opaque for the first time, right there in your kitchen. The chickpeas already went through their one structural change, hours or months earlier in someone else's kitchen, and this pot is only warming them through and coating them in sauce.
Why chicken has a narrow window and canned chickpeas don't
Muscle is built from long protein fibers — mostly myosin and actin — that sit loose and translucent in raw meat. Heat forces them to denature: the fibers unfold, then clench back together into a tighter, opaque structure. That clenching is what "cooked" looks like in a chicken breast, and it happens inside a fairly narrow temperature band. Miss the low end and the center stays raw and springy. Push past the high end and the same clenching that made it firm keeps squeezing water out, and the breast turns dry and stringy. Chicken Piccata and Chicken Milanese both pound the breast flat before it ever hits the pan for exactly this reason — an even thickness means every part of the piece crosses that narrow band at roughly the same moment, instead of the edges finishing while the center is still translucent.
A chickpea has nothing like that waiting for it. A canned chickpea was already cooked under pressure at the cannery — its cell walls broke down and its starch gelatinized months ago, and that's the one structural change a chickpea gets. Add it to a curry and stir it through the spices, and the heat isn't finishing anything raw. There's no undercooked chickpea waiting to happen. Leave it in a simmering sauce too long and it doesn't dry out and toughen — it just keeps softening, sliding slowly toward mush, which is a different failure than the one waiting for the chicken in the same pot.
Tofu, tempeh, and seitan already set before they reached your kitchen
Tofu's turning point isn't heat at all. Soy milk is a suspension of protein that doesn't hold a shape on its own; a coagulant — usually a mineral salt or an acid — is stirred in while the milk is still hot, and that's what links the protein into the solid gel you buy as a block. The coagulation happened at the maker, not in your pan. Tempeh's binding event is different again: a mold grown through cooked soybeans knits them into a cake with its own mycelium, a fermentation step finished well before the package reaches a store shelf. Seitan is different still — its structure comes from a gluten network built by hydrating and working wheat flour, then set with heat during preparation, usually before it's sold as seitan at all.
None of the three is raw the way a chicken breast is raw. A pan can still brown the surface of any of them and drive off water at the edges, but it isn't triggering the one big structural event the way it does for meat, because that event already happened somewhere else.
Pressing removes tofu's water; heat removes meat's
Both materials hold water inside a protein structure, and both can lose it — but the mechanism pulling it out is different, and so is the tool a cook reaches for. Meat's water gets squeezed out actively, by muscle fibers contracting as they heat; the longer or hotter you cook it past done, the more that contraction wrings out, which is why resting a cooked piece — letting the fibers relax again — helps it hold onto what's left. Tofu's water sits passively in the pores of an already-set gel, and it comes out mechanically, under the weight of a press, well before any heat is involved. Frying or simmering tofu too long can still tighten that gel and squeeze a little more water out at the margins, producing the same rubbery, overcooked texture an egg custard gets from too much heat. But that's a gentler, later-arriving version of what happens to meat, because tofu starts the pan already most of the way to done.
How much of the difference is just water
Weigh them and the gap is smaller than it looks, and a lot of what remains is water rather than protein. Per 100 grams, a firm block of tofu made with calcium sulfate carries 17.3 grams of protein against 69.8 grams of water. Tempeh carries 20.3 against 59.6. Roasted chicken breast carries 29.8 against 62.4.
Tofu and tempeh are both soybeans, and tempeh's lead is mostly the okara — tofu throws away the fiber and hull fragments that tempeh keeps, then holds pressed water in their place. So the press is not only a texture decision. Squeezing water out of a block concentrates everything else in it, which is the same lever, pulled for a different reason.
The other axis is which amino acids a protein carries. Plants generally run short on one of the indispensable ones — cereals on lysine, most legumes on the sulphur amino acids — and soy is the common exception that is not notably short on any. The FAO's scoring method, DIAAS, exists to put a number on exactly that: how much of each indispensable amino acid a food delivers, adjusted for how much of it is actually absorbed.
That is a compositional fact about the food and not advice about a diet. What it changes at the stove is small but real: a dish leaning on rice or bread for its protein is working from a different amino acid profile than one leaning on soy, and the traditional pairings — beans with rice, lentils with wheat — land where they do because each side covers the other's short one.
The one plant protein still waiting to be cooked
Dried, uncooked beans and lentils are the real exception, and the reason is that nobody has run them through their one structural change yet. Raw, they're hard enough to chip a tooth on, because the cell walls holding their starch are still intact; only sustained moist heat breaks those walls down and lets water into the starch inside. That's a genuine transformation still waiting to happen in your own pot, the same way it is for a chicken breast — undercooked dried beans are unmistakably wrong, chalky and hard rather than tender.
Red kidney beans carry a real stake in getting this right. They hold a lectin, phytohaemagglutinin, that a bare simmer does not reliably destroy — and the temperature a slow cooker holds is squarely in the range that fails to. The FDA's instruction is to soak them for a minimum of five hours and then boil them in fresh water for at least thirty minutes, before they go anywhere near a low-and-slow pot. Canned kidney beans have already had this step done for them industrially, which is the last piece of the pattern: whichever plant protein arrives already transformed, the pan's job shrinks down to flavor and temperature. Whichever one hasn't, the pan is doing the same first-time work a raw chicken breast needs.