Meringue
Egg white foam stabilised by sugar, in three versions with quite different stability — and the ingredient that ruins all three is fat.
What makes it set
A stabilised foam, and Protein setting
A baked product is set by the oven. This one is not — and what sets it instead decides almost everything that can go wrong with it. See the whole family by mechanism.
Also called french meringue (INTERNATIONAL), swiss meringue (INTERNATIONAL), italian meringue (INTERNATIONAL), egg white foam (INTERNATIONAL)
Meringue is air beaten into egg white and held there by sugar. Whipping unfolds the white's proteins so that they spread into films around the air bubbles; sugar dissolves into the water between them and makes that liquid thick and slow-draining, which is what stops the foam collapsing while it waits.
There are three, and they are not interchangeable. FRENCH is raw: sugar beaten into whipped whites. It is the lightest, the least stable, and the one that must be baked or folded quickly. SWISS heats the whites and sugar together over water until the sugar has dissolved, then whips — denser, glossier, considerably more stable. ITALIAN whips the whites and pours in a hot sugar syrup, cooking them as it goes; it is the most stable of the three and the one that holds for hours on a pie.
Baked low and long, a meringue dries out into something crisp all through. Baked hot and briefly, it browns on the outside and stays soft in the middle — a pavlova is deliberately the second, with acid and starch added so that the inside stays marshmallowy rather than setting.
What holds it together
Air cells surrounded by films of partly unfolded egg white protein, with the water between them thickened by dissolved sugar. Heating coagulates the protein and fixes the structure; without heat the foam is stable only for as long as the liquid takes to drain out of it.
Follows from BakeHQ's protein coagulation record and its egg white ingredient record, which carry the citations for the thermal behaviour of egg white protein.
RecordedFollows from evidence recorded elsewhere on BakeHQ
What temperature does to it
A raw meringue is not set at all and drains steadily at any temperature; warmth speeds it up. In the oven the useful distinction is not hot against cool but whether the intention is to dry it or to brown it, and the two want opposite settings. Dried slowly it becomes crisp throughout and cracks if it is cooled quickly, because the outside contracts around a still-expanded inside — which is why meringues are usually left in a switched-off oven rather than taken out.
RecordedFollows from evidence recorded elsewhere on BakeHQ
How it keeps
A dried meringue keeps for weeks in a sealed container in a dry place and goes chewy within hours of meeting damp air, because the sugar in it is hygroscopic. It cannot be stored with anything moist, including the cake it is meant to go on. A raw or lightly cooked meringue topping does not keep at all and is at its best within a few hours.
Follows from sugar's hygroscopicity, recorded on BakeHQ's sugar pages.
RecordedFollows from evidence recorded elsewhere on BakeHQ
What a good one is like
- Structure
- Holds a stiff peak that does not fold over; the bowl can be inverted
- Texture
- Completely smooth rubbed between finger and thumb — any grain is undissolved sugar
- Colour
- Bright white when raw; evenly pale gold if browned deliberately
Where it stops
Meringue tolerates no fat whatever. A trace of yolk, an oily bowl or a plastic bowl that has held something greasy will prevent a foam forming at all rather than merely weakening it, and there is no recovery — the whites have to be replaced. It also cannot be made in advance in its raw form, and it is a poor filling for anything that will be refrigerated with it, because it draws water out of whatever it touches and gives water back to the air. Aquafaba will whip into something that looks like a meringue and behaves differently, and BakeHQ's aquafaba record records the limits of that specifically.
The grain test, and the two minutes in which it is still fixable
Rub a little raw meringue between finger and thumb. If it feels smooth, the sugar has dissolved. If it feels sandy, it has not.
That is the whole test, and it is worth doing every time, because undissolved sugar is the cause of both of the two most common finished faults — weeping and a chewy layer at the base — and it is entirely correctable at the point the test is done and entirely uncorrectable ten minutes later.
Undissolved sugar draws water out of the protein films by osmosis. In the oven that water has nowhere to go but out, and it appears as amber beads on the surface or as a syrupy layer underneath. Both are sugar syrup, which is why they taste sweet rather than eggy.
The fix while it is still raw is to keep whisking, or to warm the bowl gently over water until the grain disappears — at which point it has become a Swiss meringue, which is a reasonable place to end up.
Related
Things that go wrong
Meringue is weeping, chewy or will not whip
Undissolved sugar and fat contamination are both faults of the foam, and neither depends on what the meringue was for.
Used on and in
The shell IS a meringue with almond in it, which is why every macaron fault traces back to the foam.
What it is built from
The protein that forms the films around the air. A trace of yolk fat in it prevents the foam entirely rather than weakening it.
Caster rather than granulated because it dissolves into the whites far more readily, and undissolved sugar is what weeps.
The science behind it
Unfolding at the air interface is what makes the foam; setting on heat is what fixes it.
Keep reading
Buttercream
Sets by solid fat rather than by a stabilised foam, which is why the same complaint means something different in each.
Meringue is weeping, chewy or will not whip
Work through what you can actually observe, rather than a list of possibilities.
Fillings, icings and creams
The whole family, grouped by what sets each one.