Mousse
A mousse is an aerated dessert in which lightness comes from folding air into a stabilised base. Three components decide the outcome: the flavour base (purée, chocolate, anglaise), the aerator (whipped cream or meringue) and the stabiliser (gelatine, chocolate or starch).
The order and temperature of combining matter. The base is brought to around 30–35 °C: too hot and the whipped cream collapses, too cold and the gelatine starts setting in lumps before it is folded through. The aerator goes in in stages, with folding strokes, to keep the bubbles.
Density is set by the proportion of aerator: more gives a lighter texture but a less stable structure. Mousses built on whipped cream come out denser and more dairy-forward; those built on meringue lighter and airier.