Boiling over

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In kitchen language, boiling over is the term used to describe excessive foam formation when liquids are boiled and the resulting overflow of the contents of the pot. The risk of boiling over exists especially with liquids with a relatively high proportion of protein or starch, such as milk or the cooking water from potatoes , pasta , rice and legumes , also with broth before skimming . The egg white coagulated by the heat or the gelatinized starch stabilizes the gas bubbles that arise during boiling , which only burst after a delay and, as foam, can increase the volume of the contents of the pot many times over. Since the phase transition of the water from liquid to gaseous takes place suddenly when the boiling point is reached, the liquids in question boil over suddenly.

If the cooker boils over, not only is cooking liquid lost, which contaminates the stove, it can also lead to dangerous situations if the flame goes out on gas stoves or if the largely emptied pot is overheated on other stoves.

To prevent boiling over, the food should be heated to a moderate temperature and observed. The use of a milk monitor , a disc lying on the bottom of the pot, leads to a rattling warning tone just before the liquid boils. The addition of fat or vegetable oil at the beginning of the cooking process reduces foam formation, as fat molecules combine with the water-hostile parts of protein molecules and thus reduce their ability to envelop gas bubbles. It is physically impossible to boil over when heating liquids in a water bath or in a simmering pot , since the food only comes into contact with the maximum temperature of 100 ° C and is only heated to just below the boiling point.

In the microwave oven heated water, by bumping boil over, the other causes has in protein than the boiling over and starchy liquids. Under suitable circumstances (very clean, smooth-walled vessel) the nucleation of gas bubbles necessary for the phase transition can be delayed so that water remains liquid at a temperature of up to about 110 ° C. The overheated water can start to boil explosively due to disturbances such as movements (when removing from the stove) or the addition of tea bags, sugar, etc. This can be prevented by using a spoon or something similar that is placed in the vessel before heating, which promotes the formation of germs.

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