Chocolate Truffle Centers Cool the TongueTo begin, when the truffle is put into the mouth and the mouth is closed, all the heat energy thereafter comes from within the mouth, especially from the tongue. The temperature of the tongue generally remains constant and is higher than that of the truffle and the melting point of the truffle center.
The outer chocolate of the truffle melts slowly. But if we chew the morsel rather than let it melt, we won’t notice a change in temperature. The center ball of chocolate, however, has a lower melting point (it is designed that way) and so melts quickly. We note the sudden cooling of the tongue.
Going Through a “Phase”The change from a solid to a liquid is called a phase change. It occurs at a specific temperature or within a narrow temperature range. When the temperature is below that melting temperature, adding heat raises the temperature. However, once the melting point is reached, the temperature stops rising. Any additional heat energy is channeled into the melting process. After melting is achieved, additional heating continues to raise the temperature.
Compare this with a well-known substance, H₂O. Ice at 0ºC turns into 0ºC water. The temperature of the H₂O has not changed, the phase has.
FinallyThe center of a truffle is designed to melt quickly in a narrow temperature range. The center thus melts quickly. Energy is depleted from the tongue faster than it replenishes. Tongue temperature plummets.
After the center melts, tongue temperature returns to normal. The temperature of the liquefied chocolate also rises. It would reach the tongue’s temperature, except we swallow the chocolate first. Better living through chemistry!
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