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Quiche puffed up and then sank

It domed impressively through the oven door and had sunk into a dip by the time it reached the table.

Usually established at: mixing

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 was the egg and cream mixed?
Has the oven been checked against a separate thermometer?

All 2 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.

Air was beaten into the custard before it went in

Very common

Whisking hard, or beating at speed in a mixer, folds air into the mixture. In the oven that air expands and the setting egg holds it, so the filling domes or souffles well above the rim. Nothing in a custard is built to keep that volume — there is no gluten and no starch network — so as it cools the air contracts and the surface sinks, usually below where it started. A cracked, sunken top on a cheesecake and a quiche that puffed and then fell are the same mechanism in two products.

What to change

  • Mix the custard slowly, and stop as soon as it is uniform

    Combine with a whisk used gently, or a mixer on its lowest setting, keeping the whisk under the surface. Scrape the bowl and fold rather than beating to clear lumps. If the surface has a layer of foam before it goes in the oven, let it stand a few minutes and skim it.

    Any baked custard filling, and especially cheesecake batter made in a stand mixer.

    Trade-off: Takes longer to get smooth, which is why bringing the ingredients to room temperature first matters so much.

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

  • Mix the custard slowly and skim any foam before baking.
  • Bake at a moderate temperature — a hot oven makes the filling behave like a souffle.

A quiche that puffs is telling you it is behaving like a souffle

A custard has nothing to hold on to expansion with. No gluten, no starch network, nothing that sets into a rigid frame. So when a quiche rises dramatically, what has risen is air and steam held in a soft, still-setting egg matrix — and the moment it cools, it comes back down.

This is not a fault of the recipe so much as a sign that the mixture was aerated, the oven was too hot, or both. The sinking is not a separate event; it is the same air leaving.

Related

Where this happens

  • Quiche

    Modelled separately from the watery fault because the mechanism is air rather than water.

Possible causes

  • Air was beaten into the custard before it went in

    Air whisked in is the usual reason a custard behaves like a souffle.

  • The oven runs hotter than its dial says

    Steam generated faster than it can leave lifts the filling even when no air was beaten in.

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

Keep reading

  • Quiche

    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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