When boiling a substance, the substance is poured into a gas form: gas bubbles arise. Each bell needs a starting point. When cooking ordinary tap water, crystals and impurities in the water provide such a starting point.
In the case of purified substances, these starting points are no longer present in the liquid. As a result, a liquid is heated to above the boiling point without the formation of gas. If, for example, the solution finds some crystallization cores, for example, the solution will boil until the temperature has dropped to a temperature that is present at the pressure.
This process can be very violent: a crystallization core caused by vibration will also cause vibrations due to the formation of a gas bubble and cause new cores. The result is a chain reaction. In the worst case, thousands of new kernels start to cook in a fraction of a second.
Cooking delay can be avoided by using cooking stains. So-called boiling pearls can also be used, but because they are of glass (with a very smooth surface), it works less well. A stir flake or fish (a teflon melted magnet that is moved by a spinning magnetic field) also works well. Also see
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