Demonstrating a chocolate emulsion, Barcelona-based pastry chef and chocolatier Ramon Morató whisked vanilla water into melted chocolate. After a moment, he held up the whisk and a grainy, tough mixture plopped into the bowl.

“Our chocolate is completely broken,” he said in a thick Spanish accent as the audience laughed. “This is a disaster. This is not my chocolate.”

Amid residual chuckles, Morató added the rest of the water.

“We frictionate our chocolate,” he said. At last, the chocolate became smooth and thick. The audience had been tricked, but applauded nonetheless.

Morató spoke Monday with the occasional assistance of a translator as part of the public lecture series accompanying the Science and Cooking undergraduate course at Harvard. His lecture, titled “The Many Faces of Chocolate,” explored the importance of temperature in working with cocoa.

Throughout the lecture, Morató waved around a temperature gage.

“For us, the thermometer is a third arm,” Morató said.

Science and Cooking Professor David Weitz began the lecture with an explanation of the phase transitions of milk, relating them to the behavior of chocolate and the fact that cocoa butter can form a variety of crystals when solidified. Weitz described the method of tempering chocolate, in which chocolatiers heat and cool chocolate around its melting point, to reach a preferred crystal structure.

“By controlling the kinetics of these phase transitions, experts in chocolate can control the way chocolate behaves,” Weitz said.

Morató did just that. He described and occasionally demonstrated six applications of chocolate: melted chocolate, chocolate emulsion, chocolate mousse, molten chocolate cake, velvet effect technique, and thermal shock technique.

Each example elicited murmurs of hungry delight throughout the packed lecture hall. The velvet effect technique—presented in a series of photos—involved spraying a frozen, chocolate chicken with hot, liquid chocolate, creating a surface that mimicked velvet. Morató mentioned that he used that method a few weeks ago for a tart at actress Salma Hayek’s wedding.

During the final example, Morató poured melted chocolate onto a frozen marble tray. The chocolate hardened and was elastic for a few seconds before becoming brittle. In those seconds, Morató bent the chocolate into a structure resembling a crumpled-up tissue. The crowd laughed at the lack of artistry but quieted when Morató presented pictures of his other delicate, intricate designs.

Morató also taught the audience how to best enjoy chocolate.

“Who eats chocolate? The humans. Which is our corporal temperature?” Morató paused and pointed his temperature gauge into his assistant’s mouth. The audience laughed heartily. “36! One degree more or less than the melting point. If we are gourmets, we let it melt. At that moment, we can taste the product in our mouth at its best.”

Morató’s lecture attracted an audience from the greater Cambridge area. Before the lecture, people waited in a line that winded around the Science Center.