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Macarons cracked on top

The shells looked right going in and came out with a fissure across the top, sometimes a single split and sometimes a shattered surface.

Usually established at: baking

Narrow it down

Answer what you can. Anything you skip simply leaves its causes in play — there is no requirement to answer everything, and no answer is treated as more authoritative than what you actually saw.

Before the tray went in, did the shells have a skin — could you touch one lightly without batter coming away?
What did the piped shells look like a minute after piping?
Were the trays rapped down firmly after piping?
Has the oven been checked against a separate thermometer?

All 4 possible causes are shown below. Answer a question above to start ruling them out.

Every possible cause

The complete model, whatever you answered above. Each cause states the mechanism — what physically happens — because a cause without a mechanism is folklore with a confident tone.

The shells went in before a skin had formed

Very common

A piped shell left to stand loses surface moisture and forms a skin that is dry to the touch. That skin is what makes a macaron behave differently from any other piped meringue: it resists the steam generated underneath, and the steam takes the only path left to it, lifting the shell away from the tray at its edge. That lift is the foot. Without a skin the surface is the weakest point, so the steam goes straight up and splits it. Humidity is the usual reason a skin does not form in a normal resting time — the air is already close to holding as much water as it can, so the surface has nowhere to lose it to.

What to change

  • Rest the piped shells until they are dry to a light touch

    Leave the piped trays uncovered and touch the edge of one shell lightly. When no batter transfers to your finger and the surface feels matt rather than tacky, the skin has formed. In a humid kitchen this can take far longer than a recipe's stated time, or fail to happen at all — running an extractor, a dehumidifier or simply not making macarons on a wet day is more reliable than waiting longer.

    Any macaron, and any piped meringue that is meant to rise away from the tray.

    Trade-off: Resting too long is also possible: a shell left for hours can dry unevenly and bake with a dull, blotchy surface.

The oven runs hotter than its dial says

Common

Domestic ovens routinely differ from their dial, often by enough to change a bake materially, and the offset is usually consistent. An oven running hot drives moisture off faster and sets and browns the outside before the inside is done, so a cake following its recipe exactly comes out dark and dry at the edges and sometimes underdone at the centre. The counterpart cause, an oven running cool, is recorded separately because it produces almost the opposite crumb.

What to change

  • Test for doneness rather than trusting the time

    Start checking well before the recipe’s time is up. A skewer should come out with a few moist crumbs rather than clean — a genuinely clean skewer usually means the cake is already slightly past its best. The cake should also be just beginning to pull away from the sides of the tin and spring back when pressed lightly.

    Any cake, and particularly in an oven whose real temperature is unknown.

    Trade-off: Opening the door early matters for a cake that is still rising, so check late rather than often.

The batter was not folded down far enough

Common

Macaronage deliberately deflates part of the meringue until the batter will flow. Stopped early, the batter holds every mark made in it — the peak left by the tip, the ridges from the spatula. Those features dry in place, so the surface is uneven when the skin forms and the shell has thick and thin regions. Steam leaving a thick region has to break a thicker skin, and it breaks it unevenly.

What to change

  • Fold to the ribbon, and test before piping the whole tray

    Fold, then lift the spatula and let the batter fall back. It should run in a thick continuous ribbon and the trace it leaves should sink back into the surface in roughly ten to twenty seconds. Batter that breaks into lumps needs more folding; batter that vanishes immediately has had too much. Pipe one shell and watch it: if the peak from the tip settles flat on its own, the batter is right.

    Every macaron batch. The number of folds depends on the meringue, the bowl and the spatula, so a count copied from a recipe is not transferable.

    Trade-off: Costs a minute, and the test itself deflates a small amount of batter.

Large air pockets were left in the piped shells

Common

Piping folds air into the batter and traps bubbles against the tray. A large bubble sitting just under the surface has very little batter above it, and that thin roof both dries fastest and has the least to resist the bubble expanding underneath it in the oven. Rapping the tray firmly brings those bubbles up and breaks them before the skin forms, which is the whole reason for a step that otherwise looks like superstition.

What to change

  • Rap the trays down firmly before resting the shells

    Drop each piped tray flat onto the worktop from a few centimetres, several times, rotating it between drops. Burst any bubbles that surface with a cocktail stick. Do this before the shells are rested, because once a skin has formed the bubble is sealed in.

    Piped macarons. Harmless to almost any piped batter that is meant to bake flat.

    Trade-off: None worth naming, beyond the noise.

Preventing it next time

  • Rest the piped shells until they are genuinely touch-dry, and accept that on a humid day this may not happen.
  • Rap the trays down hard enough to bring bubbles up, and burst the ones that surface.
  • Verify the oven with a thermometer rather than trusting the dial — macarons are unusually sensitive to a hot oven because the shell sets so early.

Why a skin is what makes a macaron a macaron

Almost every macaron fault, cracking included, comes back to one question: where does the steam go?

A rested shell has a dry skin on top and wet batter underneath. When the steam arrives it cannot get through the skin, so it lifts the shell at its weakest edge — the join with the tray — and that lift is the foot. The skin is not a cosmetic step and it is not about drying the batter out; it is the thing that decides the direction the shell expands in.

Without it, the top is the softest surface and the steam goes straight up through it. That is a crack. It also explains why the same batch can crack and have no feet at once: those are not two problems, they are one.

Related

Where this happens

  • Macaron

    The commonest reported macaron failure, and the one whose folk explanations vary most widely.

Possible causes

  • The shells went in before a skin had formed

    The single most common explanation, and the one that also accounts for missing feet in the same batch.

  • The oven runs hotter than its dial says

    A shell that sets early has less surface able to yield, so steam breaks it rather than stretching it.

  • The batter was not folded down far enough

    An uneven surface dries to an uneven skin, and an uneven skin fails at its thinnest point.

  • Large air pockets were left in the piped shells

    Explains a crack directly over a visible cavity rather than a crack across the whole top.

If none of this matches what you saw, the model has a gap. Tell us — that is how this section gets better.

Keep reading

  • Macaron

    What the thing is supposed to be like, which is where most diagnoses actually start.

  • Why baking fails

    The small number of things that go wrong underneath the large number of ways it shows.

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