Icing, glaze and ganache are the same idea at three ratios

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

Ratio does almost all the work

A glaze, a spreadable icing and a firm covering can all be made from the same two ingredients in different proportions. More liquid gives something that flows and sets thin, while more solids give something that holds a shape. This means most icing problems are a ratio problem rather than a technique problem, and they are fixed by adding one side or the other.

Adding liquid a very small amount at a time is essential, since the transition from thick to runny happens quickly. Understanding the ratio also means you can make any of the three without a specific recipe for it.

Fat determines the room-temperature behaviour

A mixture built on fat, whether butter or the cocoa butter in chocolate, is firm when cool and soft when warm. A mixture built on sugar and water sets by drying and crystallising rather than by cooling, and it stays set in warmth. That is why a water-based glaze survives a warm room while a butter-based one does not.

It also explains why one type must be refrigerated and another must not, since cold makes fat-based coverings hard and dull. Choosing between them is therefore a practical decision about where and when the item will be eaten.

Ganache and the emulsion problem

Chocolate and cream form an emulsion, with fat droplets suspended in the water phase of the cream. It splits when the emulsion breaks, which usually happens from overheating or from adding liquid too quickly. A split ganache often comes back with a small amount of warm liquid whisked in gradually from the centre outwards.

The ratio of chocolate to cream determines whether it pours, spreads or sets firm enough to be rolled. Different chocolates contain different amounts of cocoa butter, which is why a ratio that works with one can fail with another.

Temperature at application

A glaze applied warm flows into a thin even layer, while the same glaze applied cool sits in ridges. A covering applied to a warm cake melts and runs off, which is why complete cooling comes first. Butter-based icings need to be at a workable temperature, since too cold tears the surface and too warm slides.

At the stove, chilling a cake briefly before applying a final coat firms the crumb and reduces the crumbs that come away.

These are small procedural details that make the difference between a tidy finish and a messy one.

The crumb coat and why it exists

A thin first layer traps loose crumbs against the cake so the final layer goes on clean. It is allowed to firm before the second layer, which takes a short time in a cool place. Skipping it is the main reason a home-iced cake has crumbs suspended visibly in the surface.

The part that matters: the same principle applies to a glaze, where an initial thin coat gives the second one something smooth to sit on. It costs a few minutes and it is the single largest improvement available to the appearance of a finished cake.

Fixing common faults

An icing that is too thin needs more solids rather than time, since it will not thicken meaningfully by sitting. An icing that is too thick and tears needs a very small amount of liquid worked in gradually. A grainy sugar icing usually contains undissolved sugar, and sieving the sugar before mixing prevents it.

The part that matters: a dull chocolate covering has usually been cooled too fast or too cold, which affects how the cocoa butter crystallises. Each of these is diagnosable from the appearance alone once you know which of the three types you are dealing with.

The takeaway

Decide whether you want it to pour, spread or set, then adjust the ratio rather than hunting for a different recipe.

The good version is the one you can make on a Wednesday.