The race between structure and steam
A raw aquafaba foam is mostly air, held in place by a film of dissolved protein and saponins — soap-like molecules that stabilise the bubble walls. That film is still liquid. Put it in a fierce oven and the water turns to steam before the proteins have time to denature and cross-link; the walls rupture, the bubbles merge, and the foam collapses into a puddle with a crust on it. What you are managing in the oven is a race: structure must win before moisture escapes.
The mechanism is straightforward. Aquafaba proteins — largely legumin-type globulins leached from the chickpea during cooking — begin to denature and aggregate somewhere above 70 °C. As they aggregate, they form a semi-rigid network throughout the bubble walls. Once that network is in place, the foam can lose water without losing shape, because the solid scaffold holds the geometry even as the film thins. The goal is to reach that setting temperature slowly and evenly, so the interior gels before the surface dries and seals.
That is why the standard approach uses a low oven — typically 90–110 °C — for a long time. An hour and a half to two hours is common for a meringue of modest thickness, with the oven door left slightly ajar or cracked open to allow moisture to escape gradually rather than building up and then escaping all at once. Too fast, and the exterior browns and hardens while the interior is still wet; on cooling, the trapped steam condenses and the centre weeps or sinks. Too slow — below 80 °C — and the proteins never fully set, leaving a chewy, sticky mass that softens completely once it cools into a humid room.
Thickness matters because heat moves through the foam by conduction, and foam is a poor conductor. A thin meringue disc, a centimetre or less, dries through reliably at 100 °C. A tall pavlova-style mound requires either more time, a slightly lower temperature, or a deliberate strategy of residual heat: turning the oven off and leaving the meringue inside as it cools, so the core continues to set without the surface taking further colour.
Colour is a signal, not a target. The pale ivory of a properly baked aquafaba meringue means the proteins set without the Maillard reaction running away — there is very little reducing sugar in aquafaba to drive browning, so any significant darkening usually means the surface temperature exceeded roughly 140–150 °C, which indicates the oven was too hot from the start.
Once cool, the network is self-supporting. It is, in a sense, a dried protein foam — the water is gone, the structure remains.