Desserts

Why a cake sinks in the middle

A cake that rises then drops is almost always one of five causes, and each leaves a different tell you can diagnose from the shape of the dip.

By Updated 5 min read
A Victoria sponge cake, risen evenly and filled with jam and cream.
Photo: Victoria Spongebob, via Wikimedia Commons (CC BY-SA 4.0).

Key takeaways

  • A sunken centre almost always means the crumb had not set before the cake left the oven.
  • Too much raising agent makes the rise worse, not better.
  • The oven door matters early in the bake and much less later on.

A cake that rises confidently in the oven and then drops into a crater as it cools is one of the more demoralising things baking does. It looks like bad luck. It is almost always one of five things, and each has a different tell, so you can usually diagnose it from the shape of the failure.

What holding a cake up actually involves

Two separate structures are doing the work. Gas bubbles, from baking powder or soda and from air beaten into the fat, expand in the heat and push the batter up. Meanwhile the egg proteins coagulate and the flour starch gelatinises, forming a solid framework around those bubbles. The cake stays risen only if the framework sets before the gas runs out.

Every cause of sinking is a version of the same problem: the gas peaked before the structure was ready to hold it.

Gas expansion against structure setting, across a thirty-minute bakeTwo curves plotted against bake time. Gas expansion from the raising agent rises quickly, peaks early in the bake and then tails off. The structure formed by coagulating egg protein and gelatinising starch rises later and more slowly. Until the structure curve overtakes the gas curve, the cake cannot hold itself up, and a shaded band marks that vulnerable period. A dashed line at twenty-two minutes marks three quarters of a thirty-minute bake, the point after which opening the oven door is reasonably safe.Every sunken cake is the same problem: gas peaked before the structure was readyvulnerable: structure cannot yet hold the gas22 minstructure now holds;door can opengas expansionraising agent + beaten-in airstructure settingegg protein + starch010152230 minOpening the door early, too much raising agent, or an underbaked centre all move the same two curves out of step.Excess sugar pushes the green curve to the right; excess raising agent pushes the amber curve up and left.
The diagnosis in the sections below all reduce to this picture. Adapted from the mechanism described above; the curves are schematic, illustrating the relationship between the two processes rather than measured values for any particular recipe. Diagram by HRITU.

1. The oven door opened too early

The most common cause by a distance. Opening the door drops the oven temperature sharply and lets a wave of cool air across a cake whose structure has not yet set. The partially expanded bubbles contract and the top falls.

The tell: a broad, shallow dip across the whole top, and a cake that is otherwise cooked properly.

The fix: do not open the door for the first three quarters of the bake. For a 30 minute cake, that means nothing before 22 minutes. Use the oven light.

2. Too much raising agent

This is counter-intuitive, so it catches people out. Extra baking powder does not make a taller cake. It makes bubbles that grow too large, too fast. Large bubbles merge into larger ones, rise to the top, and burst, and the structure left behind collapses into the space.

The tell: a cake that rose very high, domed dramatically, then sank deeply in the centre. Often with a slightly coarse, tunnelled crumb and a faint soapy or metallic aftertaste.

The fix: roughly one teaspoon of baking powder per 125 g of plain flour. If a recipe asks for much more than that, be suspicious of the recipe.

3. Underbaked in the centre

The edges set, the middle never does, and the uncooked centre has no framework to support itself once it leaves the heat.

The tell: the dip is dense and slightly wet, and a skewer comes out with batter rather than crumbs. The sunken part often tastes raw.

The fix: test with a skewer in the centre, not halfway out. If the top is browning before the middle is done, drop the oven by 10 °C and give it longer, and loosely cover the top with foil.

4. Too much sugar, fat or liquid

Sugar and fat both tenderise, which is another way of saying they weaken structure. Sugar also raises the temperature at which egg proteins set, so a very sweet batter needs to get hotter before it firms up, giving the gas more time to escape first.

The tell: a greasy or sticky sunken centre, and a cake that seems undercooked at any bake time.

The fix: measure by weight rather than by cup. Adding an extra spoonful of sugar to a small cake changes the ratio more than it feels like it does.

5. Overbeating after the flour goes in

Beating fat and sugar hard is right, and it is where much of the air comes from. Beating hard once the flour is in develops gluten and knocks that air back out. The cake rises on the raising agent alone, then falls.

The tell: a tough, slightly rubbery crumb alongside the dip, and often a peaked, cracked top.

The fix: fold the flour in by hand until the last streak disappears, and then stop.

Two smaller causes worth knowing

  • Cold ingredients. Cold eggs added to creamed butter can curdle the mixture, which holds air badly. Take eggs and butter out half an hour ahead.
  • The tin was moved or knocked. A jolt in the first fifteen minutes does the same thing as the door opening. So does baking on a rack that wobbles.

Can a sunken cake be saved?

Not structurally. But a cake that sank from door-opening or excess raising agent is perfectly good to eat: level the top off, or lean into it and fill the crater with cream and fruit. A cake that sank from being underbaked should not be eaten from the centre.

More baking, explained the same way

The same principle about protein setting and squeezing out water shows up in the masala omelette, and for a different kind of kitchen chemistry see why bread goes stale faster in the fridge. To serve with it, try a mint and lemon cooler.

Sources

  1. Starch gelatinization
  2. Baking powder

Frequently asked questions

For dense batters it releases oversized bubbles and gives a more even crumb. For light sponges that depend on beaten-in air, it works against you. Rule of thumb: tap gently for a rich butter cake, do not tap a whisked sponge.

It causes a cake that never rises much in the first place, which is a different failure. Test it by dropping half a teaspoon into hot water. Vigorous fizzing means it is still good.

HRITU Editorial Desk is the byline for pieces produced in-house by the HRITU editorial team. We write about cooking, travel, science and everyday knowledge, and we explain the reasoning behind what we publish rather than just stating conclusions. Every article is checked against primary or reference sources before it goes out, dated on publication, and updated in the open when we learn something is wrong. Corrections and questions are welcome at info@hritu.com.

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