The shine of a mirror glaze is optics, not a recipe. Reflection happens when the surface is perfectly flat at the microscopic level: any bubble, any irregularity scatters light, and instead of a mirror you get a matte coat. So almost every glaze fault comes down to two things — air inside the mass, and the wrong temperature at the moment of pouring.
Where bubbles come from
There is only one source: air whipped in by a stick blender. Blades working near the surface draw air down and distribute it as minute bubbles that later rise through the glaze on the finished piece.
Correct technique looks like this: the jug is tilted, the blender head is fully submerged and held near the bottom, speed at minimum. The blender is not moved up and down — that movement is precisely what folds air in. The sign you are doing it right: no vortex on the surface.
Even worked carefully, some air will get in. So the glaze always rests after blending — a minimum of 6 to 8 hours in the cold, ideally overnight. In that time the bubbles rise and disperse. Nothing compensates for skipping the rest.
Before pouring, the glaze is passed through a fine sieve: that takes off the surface foam and any stray lumps of gelatine.
Pouring temperature
The working range is 30–35 °C, and it is narrow for a reason.
Above 35 °C the glaze is too fluid: it runs off the piece leaving a thin, uneven coat with the mousse showing through. On top of that, hot glaze melts the surface of the frozen entremet, and a cloudy zone forms at the boundary — there will be no mirror even where the coat did take.
Below 28 °C the glaze thickens: it lays on heavily, with a ridge at the base, and the surface keeps the marks of the pour — the waves that never smooth out.
The exact range depends on the formula: the more gelatine, the higher the working temperature. What to watch is not a number from somebody else's recipe but the behaviour — the glaze should run off a spatula in an unbroken ribbon, not in drops and not as a sheet.
The state of the entremet
The piece must be frozen through and genuinely cold: −18 °C, not "it stood in the freezer for an hour". The point is the sharp temperature difference — the glaze sets on contact, and that is exactly why the coat comes out even.
An under-frozen entremet gives two faults at once: the glaze runs off before it can set, and the surface of the mousse softens and mixes into it.
Frost is a separate problem. If the piece has sat uncovered in the freezer it grows a crystalline rime; the glaze goes over it, the ice melts, and voids and runs appear under the coat. Store entremets sealed, and before glazing pass a palm or a spatula quickly over the surface to take off any frost.
Why the coat runs down to the tray
Three causes, and they are distinguishable by eye.
- An evenly thin coat with the mousse showing through — the glaze was too warm, or too fluid by formula.
- The glaze slid off one side — the piece was not level, or it was moved before setting.
- The glaze gathered in a ridge at the base — the mass was cold and thick, and the flow stopped too early.
Pour in one movement, from the centre, without going back over covered areas: a second pass over a setting coat leaves a visible boundary.
How much glaze you need
Substantially more than the surface area suggests: the mass has to flow freely. A practical guide is roughly two to three times the calculated volume of the coating. Economising here leaves gaps you cannot close afterwards.
Run-off glaze is collected, reheated to working temperature and used again. There is one limit: each cycle adds air and particles of mousse, so sieve it and do not keep it longer than two weeks in the cold.
What to do with a coat that has already failed
If bubbles have surfaced on a finished piece, there is no fixing it — the coat comes off with a warm knife and goes back on after re-freezing.
If the glaze lay evenly but there is no mirror and the surface is matte, the cause is usually condensation: the piece was brought out of the cold into a warm humid room and moisture settled on the glaze. That is its own subject — condensation after defrosting ruins entremets more often than any fault in the glaze itself.
Finished entremets with mirror coatings are covered in the masterclasses Guyana Cake and Noisette Mousse Cake; the neutral glaze has its own lesson.