Starch gelatinisation is what turns wet batter into crumb

What follows is an argument about starch gelatinisation, and about where the received version of it stops being true.

What a starch granule does

Flour is mostly starch, packed into microscopic granules that are largely insoluble in cold water. As the temperature rises past about 60C, the granules begin absorbing water and swelling dramatically. The internal crystalline structure breaks down, molecules leach out, and the mixture thickens into a gel.

That gel is rigid enough to hold a shape once cooled, which is why bread and cake are solid rather than liquid. The process is largely complete somewhere around 80C for wheat starch, though the exact range varies by starch type.

Where the water comes from

In a batter, water exists as free liquid, as water bound to sugar, and as water held by proteins. Gelatinisation pulls the free water into the granules, which is why a cake feels set rather than wet once baked. If there is not enough water available, the granules only partly swell and the crumb comes out dry and crumbly.

If there is too much, the excess is left over and the crumb feels damp even at the correct internal temperature. This is the underlying reason why hydration ratios in recipes are less flexible than they look.

Sugar changes the temperature

Dissolved sugar competes for water and raises the temperature at which starch can gelatinise, sometimes by several degrees. That delay gives leavening gases more time to expand before the structure sets, producing a lighter crumb.

It also means a high-sugar cake needs to reach a higher internal temperature before it is genuinely set. Reduce the sugar and the cake sets earlier, rises less, and often comes out shorter and tighter. Fat has a similar delaying effect by coating granules and slowing water access.

Retrogradation and staling

As the gel cools, starch molecules gradually reassociate into ordered structures, expelling water as they go. That process, retrogradation, is what makes bread go stale, and it is not simply drying out. It proceeds fastest at temperatures just above freezing, which is why bread stales faster in the fridge than on the counter.

Weighed out, freezing below about minus 18C effectively halts it, which is why frozen bread keeps its texture.

Reheating above about 60C temporarily reverses some retrogradation, which is why stale bread refreshes in a hot oven.

Different starches, different behaviour

Cornflour gelatinises at a similar range to wheat but forms a clearer, firmer gel, which is why it thickens sauces so well. Potato starch swells at a lower temperature and gives a very high viscosity that breaks down quickly with stirring. Tapioca gives a stringy, glossy gel that tolerates freezing better than wheat or corn.

Once the crumb sets, in gluten-free baking these differences are the main structural tool available, since there is no protein network. Blending starches is how gluten-free formulations approximate what wheat does with one ingredient.

Weigh rather than scoop wherever a recipe leaves you the choice.

Practical consequences

The reason you cannot slice hot bread cleanly is that the starch gel is still setting as it cools. The reason a cake pulled too early feels gummy is that gelatinisation was incomplete in the centre.

Weighed out, the reason a custard tart needs a lower oven than a bread is that egg protein sets well below starch temperatures. Understanding one transition explains a surprising number of separate rules across the whole subject. It is also why internal temperature is the most useful single measurement in baking.

The takeaway

Bake until the starch has set, cool until it has finished setting, and stop cutting bread hot.

Bake it badly once on purpose. The failure teaches more than the photograph.