What acidulate means
To acidulate means to add a small amount of acid, such as lemon juice, lime juice or vinegar, to water or another liquid, or directly to food. The most common use is to make acidulated water, a bowl of cold water with a little acid stirred in. Many fruits and vegetables, including apples, pears, avocados, potatoes, celeriac and especially artichokes, start to turn brown as soon as their cut surfaces meet the air. Dropping the pieces into acidulated water as you prepare them slows this browning and keeps them looking fresh.
The water does not need to taste strongly sour, and too much acid can leave the food tasting sharp. Cooks also acidulate liquids for poaching eggs, fish or fruit, where a little vinegar or lemon juice helps flavour or appearance, and they may acidulate a sauce or dressing to lift its flavour. The word is a little old-fashioned and formal, and many modern recipes simply say to add a squeeze of lemon instead. You will still see it in classic cookbooks, professional training and recipes for artichokes, salads and fruit desserts, where preventing discolouration matters.