Evaporated milk
Milk with much of its water removed and nothing added — which makes it concentrated milk, and makes it categorically different from condensed milk.
Also called unsweetened condensed milk (US); tinned milk (UK); milk vs evaporated milk (INTERNATIONAL); condensed milk (INTERNATIONAL) — USUALLY MEANS SWEETENED condensed milk, which is a different product: around half sugar by weight and not interchangeable with evaporated milk in any formula.
Evaporated milk is milk with roughly half its water driven off and then heat-sterilised in the tin. Nothing is added.
That concentration is the whole of what it does. Per gram it carries more protein, more lactose and more milk fat than fresh milk, and correspondingly less water. In a bake this gives more browning, because there is more lactose and more protein present to brown, and a richer, denser crumb.
The heat treatment also matters. Sterilising in the tin drives some Maillard browning before the tin is ever opened, which is why evaporated milk is faintly caramel-coloured and tastes cooked rather than fresh.
Diluting it roughly one to one with water gives something close to ordinary milk, and it is a reasonable substitution in that direction. The reverse — using it undiluted where milk was specified — concentrates everything, which is sometimes exactly what is wanted and is never a neutral swap.
The naming is a genuine trap. In British usage condensed milk almost always means SWEETENED condensed milk, which is around half sugar and behaves nothing like this. American recipes sometimes say 'unsweetened condensed milk' for what is sold here as evaporated milk.
What changes if it is left out
Milk works where the concentration was incidental, and does not where it was the point — a fudge or a caramel built around evaporated milk depends on there being little water to drive off. Diluting evaporated milk with an equal volume of water approximates fresh milk in the other direction.
Follows from the concentration described above rather than from a measured comparison.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
Hydration
Concentrated milk is still mostly water and still a liquid. Roughly half the water of fresh milk has been driven off, so per gram it hydrates less.
Browning contribution
More lactose and more protein per gram than fresh milk, so more of both are present to brown — and the tin has already been through a heat sterilisation that starts the process.
Flavour contribution
The cooked, faintly caramel note is Maillard browning that happened during sterilisation rather than anything added.
Can stand in for
Milk— for the liquid, when diluted — undiluted it concentrates everything
Diluting roughly one to one with water approximates fresh milk and is a reasonable swap. Using it undiluted where milk was specified is never neutral: it raises the protein, the lactose and the browning together.
Compared in
Evaporated milk vs condensed milk
One side of the comparison.
Commonly confused with
Two tins that look alike and sit beside each other, one of which is mostly sugar. The single most consequential mix-up in the dairy aisle for a baker.