A boil over, in which superheated water and other contents slosh over the sides of a pot, is one of the most dreaded kitchen accidents possible. The mess often finds its way into the inaccessible crevices of an oven, and the spilled food becomes a sticky, burned-on mess. One way to reduce the chances of a disastrous boil over is to use a boil over preventer, a tool or gadget designed especially to prevent water from over boiling.

There is no one device known as a boil over preventer, however. Some cooking experts suggest older solutions such as leaving a clean wooden spoon in the pot as it heats to boiling temperature. Another home remedy for preventing boil over is to make sure the pot is large enough for the volume of the food. Using a larger pot or less water may be an effective and inexpensive form of boil over preventer.

Boil over tends to occur whenever a ingredient added to hot water sheds a starchy coating. This coating floats on the surface of the water and forms a foamy layer over time. The foam, most notably from rice or pasta, tends to prevent natural ventilation, which makes the liquid become superheated. When the liquid becomes too hot and the foam is not skimmed off or stirred in time, a boil over can occur. In theory, an effective boil over preventer would absorb this extra heat and keep the temperature below or at the proper boiling point, or it would prevent foam from building on the surface.

A common boil over preventer found in many stores looks like a glass or ceramic disk. This type of boil over preventer is placed on the bottom of the cooking pot before the water and other ingredients are added. Eventually the boil over preventer will absorb any excess heat build-up created by an unchecked layer of foam. As long as the ceramic or glass boil over preventer is in the water, it should not be able to reach superheated temperatures and boil over the side.

Another type of boil over preventer deals with the excess foam, not the water itself. A conical device attached to the lid of a pot should draw the excess foam back into the water, thus preventing a super heating problem. Pot lids with special steam-releasing holes can also reduce the chances of boil over. One inventor has even begun to market an electric boil over preventer which consists of a small air-blowing unit and a coiled plastic hose. This high-tech boil over preventer is designed to sit next to the pot and direct a steady but gentle stream of air across the surface of the water. If the foam is not allowed to form completely across the surface, it cannot create a super heating situation.