### How Phase Changes Cause Deliciousness

#### Overview of this Week's Science

###### The transformations that occur during sous vide cooking can be represented on a one-dimensional phase diagram, such as these charts from Dave Arnold:
• Eggs undergo numerous transitions, separated by just a few degrees in temperature.
• The color of a steak changes from red to brown, as the meat becomes tougher.
• Salmon changes from raw and toothy to overcooked and dry.
###### What's special about the phase transitions that occur during cooking?
• Simple phase transitions, like freezing and boiling, are reversible. In other words, the state of the material can be entirely described by its position on the phase diagram. The material can be returned to its original phase by getting back to the same conditions (e.g. temperature and pressure).

image source

• More complicated phase changes, like cooking a steak, are irreversible; cooling the meat down does not make it raw again. The physical structure of the food has permanently changed.

#### Equation of the Week

###### Calculate the energy needed to cause a phase transition is proportional to the mass of the food; the constant of proportionality is different for different materials.
• At the macroscopic level, the energy, U, needed to cause a phase transition is related to the mass, m, by a constant, L:

$$U = m L$$

• Some common values for latent heats of melting and vaporization are:
Material Heat of
melting (J/K)
Heat of
vaporization (J/K)
ethanol 108 846
nitrogen - 199
water 334 2257

#### Beyond the Lecture

###### Chocolate chantilly

How can you transform chocolate from a solid bar into a scoopable foam? As demonstrated by Bill Yosses, chocolate chantilly is a whipped mixture of molten chocolate and warm water. Air is incorporated as the chocolate mixture solidies, leaving behind a mousse-like foam.

To read more, check out the Fooducation blog post.