Double cream
Milk fat concentrated to the point where the fat, not the water, governs the behaviour — which is why it whips and why it is a poor substitute for milk.
Also called heavy cream (US); heavy whipping cream (US); whipping cream (INTERNATIONAL)
Cream is milk with much of the water removed and the fat left behind, and the fat fraction is what the names are about: UK double cream and US heavy cream sit at the top of the range, single and light creams well below it. That fraction decides whether it will whip.
Whipping works because fat globules, partly crystallised at chilling temperature, collide and clump around air bubbles as the cream is agitated. Below roughly the double-cream fat level there is not enough fat to build that network and the foam collapses. Warm cream fails for the same reason, because the crystals that hold the structure have melted.
In baking, cream is used where richness and a soft set are wanted rather than where liquid is wanted. Its water is real, but enough of it is bound up in an emulsion with fat that treating cream as a liquid gives a far richer result than intended.
What changes if it is left out
No substitution preserves both the whipping behaviour and the richness. Lower-fat creams pour and taste similar and will not hold a foam; milk with melted butter stirred in approximates the composition and not the emulsion, so it will not whip at all.
Follows from the fat-network mechanism described above rather than from a measured comparison.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
Aeration
Partly crystallised fat globules clump around air bubbles as the cream is agitated, building a network that holds the foam. Below roughly the double-cream fat level there is not enough fat to build it, and warm cream fails because the crystals have melted.
Gluten inhibition
Cream is a fat first and a liquid second, which is why it enriches rather than hydrates.
Compared in
One side of the comparison, so it is reachable from the record a reader is more likely to land on first.
Used in
Supplies the water phase that holds the fat in suspension. Running short of it is what a split ganache has done.
Below roughly this fat level there are not enough globules to build a network, and no technique compensates.
Keep reading
Every ingredient, by what it does
Grouped by function rather than by shelf, so a substitution question has somewhere to start.