In order to boil, water must reach 212
oF (100
oC) at sea level, at which temperature water bubbles rapidly. The high temperature and agitation of boiling water are reserved for the tougher, textured vegetables and for dried pastas and beans.
A common technique is to bring a liquid to a rolling boil, gradually add the food, distributing it evenly, and then bring the liquid back to a full boil before reducing the heat so that boiling becomes gentle. A lid on the pot or pan will bring the liquid to a boil more quickly by increasing the pressure. It is always recommended to reduce the heat setting once a boil has been reached, because food will not cook any faster at a higher setting than at the one required to maintain a gentle boil. Spillovers, burns, and loss of cooking liquid form evaporation can be avoided if a gentle boil is used.
Food may also be parboiled in boiling water, after which it is removed and its cooking completed either at a later time or by a different heating method. Parboiling is used frequently in restaurant service when food must be prepared in advance and finished to order. Another use for boiling water is for blanching, which sets the color of green vegetables, loosens the skins of fruits, vegetables, and nuts for peeling, and destroys enzymes that contribute to deterioration. Foods are often blanched before being canned or frozen.
