A chocolate truffle may be a hollow sphere of hard chocolate filled with a special sort of chocolate filling. The filling inside melts in a unique way.
When you put a truffle in your mouth, the inside chocolate cools your tongue. Is that really possible? Yes it is. It is not merely a psychological effect. Chocolate truffle centers really do cool the tongue.
Chocolate Truffle Centers Cool the Tongue
When the truffle is put into the mouth and the lips close around it, energy comes from the cheeks, the palate, and especially the tongue. The temperature of the tongue generally remains nearly constant and is higher than that of the truffle’s center.
The outer chocolate of the truffle dissolves away slowly. The center ball of chocolate, however, has a somewhat lower melting point (it is designed that way) and so melts quickly. We note a cooling of our tongue, but why?
Going Through a “Phase”
The change from a solid to a liquid is called a phase change. A phase change occurs at a specific temperature or over a very 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. Additional heat energy is channeled into the melting process. After melting is accomplished, firther heating once again raises the temperature.
Compare this with a well-known substance, H₂O. Ice at 0°C turns into 0°C water. The temperature of the H₂O has not changed, the phase has.
The 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!
Note: You might also enjoy The Improbable Making and Chemistry of Chocolate