The basic method for chocolate ganache is to pour hot cream over finely chopped chocolate, let it sit untouched for a few minutes, then stir gently starting from the centre. As the cream slowly melts the chocolate, it turns into a smooth, glossy mixture.
Ganache's texture depends heavily on the ratio of cream to chocolate; the same method can produce anything from a pourable glaze to a firm truffle filling that can be rolled by hand.
Why is the cream poured over the chocolate?
Heating chocolate directly on the stove can overheat it in spots and scorch it, damaging its structure. Pouring hot cream over finely chopped chocolate spreads the heat gradually and evenly, letting the chocolate melt in a controlled way.
Letting the mixture sit untouched for 2-3 minutes gives the cream's heat time to reach every bit of chocolate; skipping this and stirring right away melts the chocolate unevenly and can leave lumps in the mixture.
Why does stirring technique matter?
Starting to stir from the very centre of the mixture in small circular motions introduces the least amount of air; air bubbles can leave dull patches and a rough texture on the surface of the ganache. Slowly widening the motion outward smooths out the whole mixture.
Stirring too fast or too hard works too much air in, and the ganache can lose its glossy, fluid look and turn dull and foamy instead.
How does the ratio determine texture?
Using cream and chocolate in equal amounts (1:1) gives a pourable glaze that can be poured over a cake. Increasing the chocolate and halving the cream (2:1 chocolate to cream) gives a ganache that firms up at room temperature into a hand-rollable truffle filling.
In-between ratios give a medium-firm ganache for cake fillings, one that holds its shape when sliced but still spreads easily with a knife; this usually comes from cream and chocolate used in roughly equal weight.
What if the ganache turns out too runny or too stiff?
If ganache turns out runnier than expected, stirring in a small amount of melted chocolate can thicken it back up. Chilling it in the fridge for a few minutes can also bring runny ganache closer to a usable texture.
If ganache turns too stiff, stirring in a little warm cream slowly is usually enough to soften it; ganache should never be heated directly on the stove, only warmed gently over a bain-marie or at room temperature.
Does the ratio change for white or milk chocolate?
White and milk chocolate contain more fat and sugar than dark chocolate, so the same cream ratio gives a softer ganache with them. That's why, for white chocolate truffles, the cream should be reduced a little and the chocolate proportion increased, or the ganache won't firm up enough at room temperature.
Dark chocolate, with its higher cocoa content, gives a much faster-firming result with the same amount of cream; this difference needs to be factored in whenever the ratio is adjusted.
Milk chocolate sits somewhere between the two; the ratio is usually found by testing a small batch and checking the texture by eye, aiming for a balance between the dark and white extremes.