Boiling, blanching, poaching, and braising all involve cooking in a pot of hot water, but that's where their similarities end.
Water is as hot as possible (212 degrees at sea level), with many large bubbles constantly breaking the surface. This method is reserved mainly for cooking pasta or starchy foods such as potatoes. Since prolonged boiling can compromise color and flavor, we don't recommend it for most vegetables.
Blanching involves quickly involving food into boiling water, then transferring it into ice water (called "shocking"). We like to blanch green vegetables—such as green beans, broccoli rabe, and snap peas—to help set their color and remove any bitterness. Blanching also helps loosen the skins of nuts or soft fruits such as tomatoes and peaches.
This technique uses water between 160 and 180 degrees (depending on the delicacy of the item being cooked), at which point small bubbles just begin to break the surface. This gentle cooking method is good for delicate foods such as fruit, fish, or eggs. The poaching liquid is often seasoned with aromatics or alcohol to induce an exchange of flavors between the food and the liquid.
This method calls for slowly simmering food in a small amount of liquid in a tightly covered pot. (The temperature of the simmering liquid is 180 to 190 degrees.) Braising is most often used for tough cuts of meat that need to cook gently until tender. Braised items are usually browned in hot oil before aromatics and flavorful liquids such as wine or stock are added.