Brinjal drinks oil in the first minute and gives some of it back in the fifth

The vegetable with a reputation for greed

Every cook who has fried aubergine has watched the oil vanish. Slices go into a generous pan, the fat is gone within moments, more goes in, and the finished dish is either heavy or dry depending on how the rest of the cooking went. It is easy to conclude that the vegetable is simply absorbent in the way a cloth is absorbent, and to fry it in resignation.

That’s only half right. Brinjal takes up a great deal of oil very fast, but it also gives a good part of it back later, and whether you end up with something rich or something waterlogged depends almost entirely on whether the cooking gets far enough for the vegetable’s second stage to happen. Most kitchens don’t get there.

The flesh is mostly air

Cut a raw aubergine and look at the cut face closely. The flesh is a loose, open network of cells with a great deal of gas between them, which is why a large fruit weighs so little for its size and why the raw texture is squeaky rather than juicy. Those air spaces are connected, and they run right up to the cut surface.

Put that structure into hot fat and two things happen at once. The trapped air heats and expands, and the water in the cell walls turns to steam and forces its way out, and every channel that empties is a channel that oil can move into by capillary action. The vegetable is not absorbing oil so much as the oil is filling a space that has just been vacated.

Then the cells collapse and push some back out

Heat eventually destroys the cell walls. Pectin between the cells breaks down, the walls lose their rigidity, and the open sponge slumps into a soft, dense mass with far less internal volume than it started with. As that happens the structure squeezes out a portion of the oil it took in, which is why a properly cooked piece of brinjal often looks oilier on the outside at the end than it did in the middle of cooking.

The timing of that turn is the thing worth watching for, and it is visible. The pieces stop looking plump and matte, the edges darken, and the surface takes on a slick sheen that was not there a minute earlier. Cooks who fry brinjal often describe waiting for it to give the oil back, which sounds like kitchen mysticism and is a perfectly accurate description of a structural collapse.

Stopping halfway is the worst outcome available. A piece taken out while it is still spongy has taken on all the oil and released none of it, and it eats as something faintly raw and unpleasantly rich at the same time. Cooking it further does not add fat; past a point it takes fat away.

Collapsing it before it meets the oil

Everything that reduces oil uptake works by wrecking that open structure in advance, before there is any fat around to fill the gaps. Salting slices and letting them sit draws water out osmotically and softens the tissue, so the sponge is already partly closed when frying starts. Steaming, roasting whole over a flame or cooking briefly in a covered pan does the same thing more thoroughly.

Thickness works on the same principle from the other end. A thin slice has a great deal of cut surface for very little interior, so it presents the maximum number of open channels per mouthful, while a thick wedge keeps most of its volume sealed behind an outer layer that browns and closes. The rounds cut fine for a quick fry are the version most likely to end up saturated.

This is why the smoky mash traditions treat the vegetable so differently from the fried ones. A whole brinjal charred over a flame never has an opportunity to take up oil at all, because it collapses in its own steam inside an unbroken skin, and any fat added afterwards is going into a structure with no empty channels left to fill.

Bitterness, browning and choosing a fruit

The old advice to salt for bitterness is a separate matter from salting for texture, and it matters much less than it used to. Bitter compounds concentrate in the seeds and in older, larger fruit, and most of what is grown now has been selected against that trait, so a young glossy specimen usually needs no treatment at all.

The browning of cut flesh is a different reaction again, driven by enzymes in the tissue meeting air, and it is cosmetic rather than a sign of spoilage. Cutting close to cooking, or holding pieces under water, keeps them pale. Heavy for its size, taut skin, and a small dry scar at the stem are better guides at the shop than size, because a light fruit for its bulk has been sitting long enough for the flesh to dry and go spongy in the wrong way.