How much egg a choux paste takes is decided by the pan, not the recipe

Most explanations of adjusting choux consistency stop at the point where it starts to matter. This one carries on.

Why the quantity moves

The first stage of choux boils water and fat together, then cooks flour into that liquid to form a thick paste. During that cooking, water evaporates at a rate that depends on your pan width, your heat and how long you stir.

A wide pan on a strong flame loses far more water than a narrow one on a gentle heat over the same period. The paste that results is therefore drier or wetter than the recipe writer's, before a single egg has been added. Egg is the ingredient that corrects for that difference, which is why its quantity has to be judged rather than weighed.

What the finished paste should look like

Correctly loosened choux falls from a spoon or spatula in a thick ribbon that breaks rather than pours. Lifting the spatula should leave a V shape that holds its point briefly before slumping. Drawn through the paste, a spatula should leave a channel that closes slowly rather than instantly or not at all.

The dough tells you first: too stiff, and the paste will not expand properly and gives small, dense buns with tight interiors. Too loose, and it spreads on the tray, rises poorly and collapses as it cools.

Adding the egg safely

Beat the eggs together first and add them in small additions, mixing fully between each one. The paste should be cooled enough that it does not scramble the egg, which shows as small set flecks through the mixture.

In the tin, hold back the last portion of egg until you have judged the consistency, since you can always add and never remove. If the paste seizes and looks curdled after an addition, keep mixing, because it usually comes back together. A mixer makes this easier but also makes it easier to overshoot, since a whole egg goes in before you can judge.

Rescuing a paste that has gone too far

A paste loosened past the point of holding shape cannot be thickened by adding flour, which would be raw in the finished bake. The usual rescue is to cook a second, small batch of the flour and liquid paste and combine the two. That doubles the quantity, so it is worth making a small correction batch rather than a full one.

At oven temperature, piping a too-loose paste into a mould or a tray bake accepts the consistency instead of fighting it.

The lesson for next time is to hold back more egg, since the last addition is almost always the one that ruins it.

Why the second cook needs a dry oven

Choux rises because water in the paste turns to steam and inflates each bun from the inside. The structure has to set around that expansion, and setting requires the surface to dry and the egg proteins to coagulate.

A humid oven or a crowded tray slows that drying, so the buns rise and then sink as the steam escapes. Opening the door early releases the steam holding the buns up before their walls can support themselves. Most recipes finish with a period at reduced heat, which dries the interior without darkening the outside further.

Piping and spacing

Choux expands considerably, so buns piped too close together share steam and end up soft where they touch. Piping at a consistent height gives even buns, since the volume of paste sets how big each one becomes. A wet fingertip flattens the peak left by the nozzle, which would otherwise scorch before the bun is baked.

Some bakers add a thin crisp topping over the paste, which controls the expansion and gives an even shape. Trays with too much grease encourage spreading, so a light coating or a paper lining works better.

The takeaway

Judge the paste with your eyes, hold back the last egg, and let consistency rather than weight decide.

Temperature and time are the same argument held at opposite ends.