The Process

• Foods are usually blanched by immersing them briefly in hot water, though in commercial kitchens powerful pressure steamers are also used. It's important to use a large pot holding lots of water, so its temperature doesn't drop below the boiling point when food is added. After boiling briefly -- two to four minutes for most foods, and even less for some -- the foods are removed to a bowl of ice water. This stops the cooking process immediately and, after a few minutes in ice water, the foods can be drained and dried for later use.

Green Vegetables

• Green vegetables, including spinach and other greens, asparagus, beans and peas, are often blanched to enhance their color. The green color in most vegetables is muted by the air trapped inside their cell walls, just as soapsuds turn clear water opaque. When the vegetables are dropped in boiling water that air expands in the heat and escapes from the cells, revealing the vivid green of the chlorophyll in the plants. When shocked immediately, the vegetables retain that green even during later cooking.

Dense Vegetables

• Restaurants also use the blanching technique for dense, slow-cooking vegetables, such as carrots or parsnips. These vegetables are blanched for a longer time than most others, often several minutes, to par-cook them. Shocking the vegetables stops the cooking, and the vegetables can then be drained and refrigerated until mealtime. When needed they can be finished after a relatively brief cooking time, allowing the cook to include long-cooking vegetables with other ingredients that cook more quickly.

Produce for Preserving

• Blanching is also important for any produce items that are to be frozen or dried for long-term storage. Contact with the boiling water kills bacteria, fungi and mold spores, insects and insect eggs that might otherwise contaminate the preserved foods. It also deactivates the natural enzymes that cause foods to decompose, which otherwise would continue working in the frozen or dried foods. Blanching and shocking fruit and vegetables before freezing or drying helps extend their storage life, and ensures better flavor and texture throughout that time.