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Food physics summary Molecular Gastronomy (FPH20806)
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A complete summary of all the food physics aspects covered during the course of Molecular Gastronomy (FPH20806)
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LECTURE 1RECENT 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
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