An egg wash is three different finishes depending on what you dilute it with

Treat the sections below as a sequence. With egg washes and finishes, getting the early decisions right makes the later ones much easier.

Why an egg browns the way it does

Egg contains protein and a small amount of sugar, which is exactly what browning reactions need at oven temperatures. The yolk also carries fat and pigment, so it contributes both a deeper colour and a richer sheen. White is mostly protein and water, so it sets to a glassy film that shines without darkening much.

Whole egg falls between the two, which is why it is the default in most recipes. The wash browns before the pastry beneath it, which is why an over-thick coating can look burnt while the bake is pale.

What the diluting liquid changes

Water thins the wash and reduces both colour and gloss, giving a lighter, more even finish. Milk adds sugar and protein of its own, deepening the colour and softening the crust slightly. Cream adds fat as well, giving a deeper, glossier finish that suits rich pastries.

A pinch of salt in the wash breaks down the egg proteins and makes it thinner and easier to brush evenly. Undiluted yolk gives the darkest finish and is the most likely to scorch or to look streaky.

Applying it without damaging the bake

Use a soft brush and the lightest pressure, since dragging a stiff brush across risen dough deflates it. Keeping the wash off the cut edges of laminated pastry matters, because egg sets and glues layers that should separate.

The same applies to the cut sides of scones and to the rim of a puff pastry case, which will not rise where it is sealed. Pooled wash bakes into a dark, slightly rubbery patch, so brush out any puddles before the tray goes in. Two thin coats, with the first allowed to dry, gives a more even colour than one heavy one.

When to apply it

Enriched breads and pastries are usually washed just before baking, once the final proof is complete. Washing before proving can dry into a skin that restricts the rise and cracks as the dough expands. Some bakers wash twice, once before proving and once after, for an unusually deep colour on a rich dough.

Chilled pastry takes the wash better than warm pastry, which absorbs it and looks patchy.

For a long bake, applying the wash partway through avoids the finish darkening past the point you wanted.

Alternatives when egg is not an option

Milk alone gives a soft, matt finish with modest colour and suits scones and soft rolls. Cream gives more colour than milk and a slight sheen without the setting behaviour of egg. A sugar syrup brushed on after baking gives a high gloss and a slightly sticky surface, which suits sweet buns.

Plant milks vary considerably in how they brown, since their sugar and protein contents differ widely. Oil gives a crisp, matt surface with no gloss at all, which is right for some breads and wrong for most pastries.

Weigh rather than scoop wherever a recipe leaves you the choice.

Reading a finish that went wrong

A streaky finish usually means the wash was too thick or applied unevenly to a cold surface. A dull finish means either too much dilution or a wash that soaked in rather than sitting on top. Dark patches at the edges suggest wash that ran down and pooled where the pastry met the tray.

Layers that failed to separate at one edge point at wash that reached the cut side of the pastry. A wrinkled, leathery surface usually means the wash dried before baking, which happens if the pastry waited too long.

The takeaway

Choose the wash for the colour you want, brush it thin, and keep it away from any edge that needs to rise.

Bake it badly once on purpose. The failure teaches more than the photograph.