Rescues · TO CARAMELIZE
The sugar crystallised into a gritty mass.
Why it happens
A stray crystal or a stirred pan seeded crystallisation. Do not stir a dry caramel; swirl the pan, and brush the sides down with water.
Recovering it
Crystallised caramel can be melted again with a little water and re-cooked, which works completely. Burnt caramel cannot; it is bitter through and should be discarded, and the pan soaked rather than scrubbed. Under-caramelised onions simply need more time and a little patience, and adding a pinch of sugar or a splash of water to deglaze speeds them without much loss.
The mechanism
Caramelisation is sugar decomposing under heat, and unlike the Maillard reaction it needs no protein at all. Different sugars start at different points: fructose from about 110°C, sucrose from around 160°C, so honey and fruit brown long before table sugar does. As it proceeds, sweetness actually falls while bitterness and aroma rise, which is why a dark caramel tastes less sweet than a pale one. This is also where the phrase 'caramelised onions' is doing two jobs — real caramelisation of the onion's own sugars, and Maillard browning between those sugars and its amino acids. Both are happening, both take time, and neither is achievable in the ten minutes most recipes claim: properly caramelised onions take closer to forty-five, and every shortcut trades depth for speed.
The full TO CARAMELIZE lesson — how to tell, where to practise it, what it carries to.