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Macarons are hollow inside

The shell lifted and formed a foot, and biting into it finds a large gap between the top and the base.

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.

How freely did the finished batter run?
What did the meringue peak do when the whisk was lifted?
How quickly did the shells take on colour?

All 3 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 batter was folded past the point of flow

Very common

The meringue supplies every bubble a macaron shell will ever contain, and macaronage removes some of them on purpose so the batter levels. Past that point each further fold removes bubbles the shell needed. A batter that runs freely spreads on the tray instead of holding a disc, and the foam that would have expanded and pushed the shell upward off the tray is largely gone — so the shell bakes flat and wide, without feet.

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.

The meringue was not whipped to a firm enough peak

Common

A macaron contains no flour, no chemical leavener and no whole egg — the whipped white is the entire structure. A meringue taken only to soft peaks has larger, less stable bubbles, and macaronage then removes them faster than it removes those in a firm foam. The batter loosens suddenly rather than gradually, which is also why an underwhipped meringue is so often overmixed as well: the window between stiff and runny is much narrower.

What to change

  • Whip the meringue until the peak stands without drooping

    Whip until lifting the whisk brings up a peak that holds its shape and points straight rather than curling over. The bowl should be clean and dry and free of any trace of yolk, since fat prevents the foam building at all. Add the sugar gradually once the whites are frothy rather than at the start.

    Macarons, and any meringue that will be folded into something else.

    Trade-off: Whipping past this point is a real fault of its own — a dry, grainy foam that will not fold in smoothly.

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.

Preventing it next time

  • Whip the meringue firm, so that macaronage has a wider window and the foam that remains is stable.
  • Stop folding at the ribbon.
  • Verify the oven temperature — a hot oven sets the shell before the inside has finished expanding into it.

A hollow shell rose correctly and then lost what was holding it up

This is the fault that most often gets misdiagnosed, because from the outside the macaron is a success: it has feet, a smooth dome and the right colour.

What has happened is that the structure inside was too weak to stay where the steam pushed it. A foam that was soft to begin with, or one that macaronage thinned too far, will expand in the oven and then subside away from the top as it cools, leaving the crust suspended over a gap. A hot oven does the same thing by a different route: the shell sets while the inside is still rising, so the inside pulls away from a top that is already fixed.

That is why the fix is almost never 'bake it longer'. A longer bake on a weak foam produces a dry hollow shell instead of a soft one.

Related

Where this happens

  • Macaron

    Distinct from the other two because the shell rose correctly first — the outside is a success and the inside is not.

Possible causes

  • The batter was folded past the point of flow

    Enough foam survived to lift the shell and not enough to keep it up once cooling began.

  • The meringue was not whipped to a firm enough peak

    The structural explanation: the foam was never strong enough to hold the volume the steam created.

  • The oven runs hotter than its dial says

    The shell sets while the inside is still expanding, so the inside pulls away from a top already fixed in place.

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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