Food physics summary Molecular Gastronomy (FPH20806)

LECTURE 1
RECENT DEVELOPMENTS IN MOLECULAR GASTRONOMY

- Cornerstone is creativity which means you do not copy  no recipe books
- Nouvelle cuisine was different from traditional French cuisine because the portion sizes were much
smaller than traditional French cuisine

Terminology

- Adaption: Adapting a recipe to ones liking
- Deconstruction: Modification of each of its elements
- Reconstruction: Takes the elements of one dish and changes their arrangement, not always changing
elements
- Non-construction: Taking ingredients and making something new out of it, without recognizable form
of a dish

The modernist cuisine

- Focusses more on the holistic approach of the eating experience and less on the techniques/skills
needed to make the food.

STRUCTURED APPROACH TO MOLECULAR GASTRONOMY

- The microstructure of food is very relevant for the material properties
- Most foods we prepare are examples of dispersed systems and the sensory properties are
determined mainly by the microstructure
- Complex Dispersed System (CDS) formalism describes hierarchical structure and nature of its
components

,LECTURE 2: THE BASICS OF COOKING
COOKING AS A HEAT TRANSFER PROSCESS

- Cooking is the transfer of energy from flame (energy source) to pan (holding food)
- Temperature: measure of the average motion of the molecules of a material
- Speed of heat flow is related to the temperature difference and to the resistance of the material to
heating
- Sensory properties of cooked food are the results of the physical and chemical changes induced by
heat
- What can go wrong in cooking?
o The amount of energy added can be problematic, too much or too little

HEAT TRANSFER MECHANISMS AND PARAMETERS INVOLVED IN HEAT TRANSFER

1. Radiation
o Transfer of heat by means of emission/absorption of electromagnetic radiation (microwave,
broilers, grills)
o No physical contact between energy source and food
o Two main types of radiation
 Infrared: electric ovens  heat absorption on the surface
 Microwave: microwave ovens  deep penetration of heat
o Problems?
 Heat is not distributed homogenously
o For most cooking techniques based on radiation, also other heat transfer mechanisms are
involved (convection)
o The colour of the food and the distance between food and radiation source play an
important role in heating
 The darker the product, the more radiation it will absorb which will most likely
result in burning
 Amount of transported energy is inversely proportional to the square root of the
distance between the food and the radiation source  increasing the decreasing
the distance by factor 2, 4 times less radiation.

2. Conduction
o Transfer of heat between objects in physical contact (braising, cooking in a salt crust)
o Most important heat transfer mechanism by which heat is transferred within food

, o Thermal diffusivity: Every material has thermal diffusivity which is the thermal conductivity
of a substance divided by the product of its density and its specific heat capacity
o Thermal conductivity: Quantity of heat transmitted through a unit thickness in a direction
normal to a surface area, due to a unite temperature gradient
o Specific heat capacity: Amount of heat needed to raise the temperature by a specific
quantity
 Dependent on the chemical composition of the food material
o Therefore, heat transport depends on
 Specific heat capacity
 Density
 Thermal conductivity
 Mechanism of heat transfer
o Conduction charts (be able to use them for the exam)
 Plotted for a certain diffusivity
 First line (left) used when food (meat) product is in the form of a cube, whose 3
dimensions are all the same
 Second line (right) is used for a steak whose length and width are quite large
relative to their thickness




 First calculate parameter T
 Using T find the F-value from the curve
 Use the F-value to find the cooking time needed

3. Convection
o Transfer of heat between an object and its environment due to fluid motion (boiling, deep-
frying, hot air ovens)
o Always important when a fluid in involved

4. Phase change
o transfer of heat because of evaporation/condensation (steaming)

, PHYSICS OF WATER IN FOOD

- water is a cooking medium but also an ingredient in our food  water is important




Figure 1: Water phase diagram


- high surface tension
- high boiling and freezing point
o due to the strong hydrogen bonds in the molecule
- expands when freezing and contracts when melting
- high specific heat capacity
o changes based on the physical phase (water, ice, steam)
- high latent heat of vaporization and fusion
- good solvent for polar compounds

Q: In the water phase diagram why does the melting point of water decrease as the pressure increases?

A: When water freezes the material tends to expand. Increasing the pressure ‘encourages’ ice to melt.

Consequences of physical properties of water

- water subtracts heat when evaporating and steam releases heat when condensing. Ice subtracts heat
when melting.
- In water-containing foods the temperature cannot be higher than 100°C until the water has been
evaporated.
- When cooking in ovens, evaporation of water from the surface of food requires heat  food
experiences a lower temperature than that which is set on the oven.
- With high relative humidity there is less water evaporation  because there is less evaporation from
the food the temperature of the food is higher which results in faster cooking
o Exception for bread/cake  delayed crust formation because there is less evaporation
o In bakers’ ovens there is an injection of steam (high humidity)  they want to delay crust
formation because for a good bread you first need expansion of the loaf and then crust
formation

COOKING TECHNIQUES

ELABORATE FROM READER FOR EXAM

1. Boiling
2. Deep-frying Described below