What acidulated water means
Acidulated water is plain cold water with a small amount of acid added, usually lemon juice, though white wine vinegar or cider vinegar also work. Its main job is to stop prepared fruit and vegetables from discolouring. Many fruits and vegetables brown when their cut surfaces are exposed to air, because of a natural reaction between compounds in the food and oxygen. The acid in the water slows this reaction down, so the food stays pale and fresh-looking while you get on with the rest of a recipe.
Globe artichokes are the classic example, because they darken very quickly as you trim them, but apples, pears, avocados, potatoes, celeriac, parsnips and Jerusalem artichokes all benefit too. To make it, stir a little lemon juice or vinegar into a bowl of cold water and add the pieces as soon as they are cut. Rubbing cut surfaces with a cut lemon is a quicker alternative for small jobs. Before cooking or serving, drain the food and pat it dry, especially if it is going to be fried or roasted.
Acidulated water is also sometimes used for poaching. You will see it in recipes for artichokes, fruit tarts, salads and root vegetable dishes.