Cold retardation
Cold retardation means holding a shaped loaf in the fridge, usually at 4–6 °C, for anything from a few hours to a day or more.
Cold slows yeast more than it slows lactic acid bacteria, so the rise nearly stops while acid production continues. The result is a deeper, tangier flavour and aroma than a fast warm proof can produce.
The second effect is practical: a cold loaf is firmer and easier to score — the blade runs cleanly and the cut opens better in the oven. It also takes the schedule out of the dough's hands, letting you bake when it suits you.
There are limits. Held too long, the dough turns excessively sour and the gluten weakens, losing spring and holding shape poorly. The right window depends on the strength of your starter, the fridge temperature and the flour, and is found by trial.