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Summary Molecular Gastronomy lecture notes
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This document contains all relevant text and images of the lectures given by G. Sala and M. Hennebelle in the course Molecular Gastronomy.
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Molecular Gastronomy lecture notesClip Sep 02 2019 – Recent developments in molecular gastronomy and structured approach to
molecular gastronomy (chapter 1, 2, and 3)
Nicholas Kurti (physicist) lecture: The physicist in the kitchen
Quote: it is a sad reflection that we know more about the temperature inside stars than
inside a souffle
Explorations of gastro-physics gaining importance
Brillat-Savarin: The discovery of a new dish does more for the happiness of mankind than the
discovery of a new star
The origin of molecular gastronomy: The scientific exploration of culinary, and more
generally, gastronomical transformations and phenomena as described by cooks or by
culinary books.
It forms part of food science that focuses on: Home and restaurant culinary transformation
and the eating phenomena.
A recipe is a function of variables: Time, temperature, details of process and ingredients.
Molecular gastronomy:
- Explain/de-mystify knowledge in cookbooks and cuisines, and structure the information
into models that capture the essence of a recipe
- Use the knowledge and models to design new dishes/technologies with desired
properties and transfer to the main public
The nouvelle cuisine is a reaction to the classical French cuisine. Light cuisine is inspired by
shorter cooking times, regional dishes, ingredients and techniques.
Systematic approach to new dishes:
1. Applying traditional techniques to extraordinary and prestigious ingredients
2. Influences of other regions
3. Search for new techniques.
A technique is a process or a combination of processes, that makes a product edible or
that induces another type of transition of the product. A concept is the basic idea behind
a dish/recipe.
Structured approach:
All foods are dispersed systems: Complex dispersed systems (CDS) formalism describes
hierarchical structure and nature of its components. Formalism is used to ‘ease the
operations of the mind’. The difficult part is the interaction between these constituents.
Clip Sep 03 2019 – The basics of cooking (chapter 4)
, Cooking: The transfer of energy from flame to pan, to cooking medium to food
Temperature: Measure of the average motion of the molecules of a material.
Speed of heat flows related to the temperature difference and to the resistance of the
material to heating. In the middle of the food product and the heating source also depends
on the speed of the heat transfer.
Sensory properties of cooked food are the result of the physical and chemical changes
induced by heat.
Heat transfer mechanisms:
- Radiation: Transfer of heat by means of emission/absorption of electromagnetic
radiation (microwave ovens, broilers, grills)
- Conduction: Transfer of heat between objects in physical contact (braising (stoven),
cooking in a salt crust)
- Convection: Transfer of heat between an object and its environment due to fluid motion
(boiling, deep-frying, hot air or baking ovens)
- Phase change: Transfer of heat because of evaporation/condensation (steaming)
1. Radiation: No physical contact between energy source and food. The two main types are
- Infrared: Electric ovens heat absorption on the surface. Red light is the strongest.
- Microwave: Microwave ovens deep penetration of heat.
For most cooking techniques based on radiation, also other heat transfer mechanisms
are involved. The colour of the food and the distance between food and radiation
sources play an important role in heating.
2. Conduction: always the most important heat mechanisms for transfer of heat within the food
- Fourier equation . Allows us to estimate the rate of heat transfer,
based on diffusivity and the gradient of temperature within the system.
- Thermal diffusivity: .
It gives you an idea of how fast heat is moving through a system.
- Thermal conductivity: Quantity of heat transmitted through a unit thickness in a direction
normal to a surface of unit area, due to a unit temperature gradient.
- Specific heat capacity: Amount of heat needed to raise the temperature by a specific
quantity (1 degree). This depends on the chemical composition
- Heat transport depends on: Specific heat capacity, density, thermal conductivity and the
mechanisms of heat transfer.
- Conduction calculation:
, - Exercise! Will also be on the exam: What is the cooking
time necessary to arrive to a certain temperature in a
product? Use the yellow diagram.
Water phase diagram:
Physics of water in food:
- High surface tension
- High boiling and freezing point
- Expands when freezing and contracts when melting
- High specific heat capacity
- High latent heat of vaporisation and fusion; When
heating water, temperature will heat up to 100 degrees
and will not change, and suddenly there is a change to a vapour state. This time is
required for the molecules to readjust before they go in phase transition.
- Good solvent for polar compounds.
Consequences of physical properties of water:
- Water subtracts heat when evaporating. Steam releases heat when condensing. Ice
subtracts heat when melting.
- In water containing food the temperature cannot be higher than 100 degrees until the
water has evaporated.
- When cooking in ovens, evaporation of water from the surface of the food requires heat
food experiences temperatures lower than those set.
- With high relative humidity, less water evaporation higher temperature of the food
and faster cooking.
Cooking techniques:
Crust formation is delayed by using steam on the breads. When the temperature of the oven
increases, the gas bubbles inside the loaf will increase as well, expanding the whole bread.
When there is no steam, the loaf cannot expand as easily. Fist expansion, then crust
formation.
, Clip Sep 04 2019 – Recap food physics
Texture definition: Texture is the whole of structural and mechanical properties of food
products as being conceived by humans by their touch, eyes and ears.
In a product: the structure is decided by mechanical properties like elasticity, viscosity,
fracture stress and yield stress. We can measure these. The consumer sees, hear and feel all
these aspects.
Elasticity, viscosity and fracture stress can all be tested using rheological techniques. Viscous
flow is for liquids, elastic deformation is for solids and viscoelastic behaviour is for most food
products.
Important rheological concepts: Record the relationship between the deformation and the
way the material opposes the deformation:
Rheology deals with the relation between stress and strain.
Simple deformations
There can be small deformations and large
deformations. Large deformations are more suitable for sensory perceptions. The modulus is
the expression of the stiffness in your mouth.
Also, in viscous materials we apply deformation. We don’t apply strain, but we apply shear
rate. The liquid that touches the turning machine has more deformation than the liquid on
the bottom. We can also stretch a certain fluid through its length.
A list of types of rheological behaviour which are all linked to the structure of a product, and
the rearrangements of that structure during an imposed flow:
- Newtonian
- Shear thinning
- Shear thickening
- Plastic flow
- Bingham flow
- Thixotropy
- Anti-thixotropy
- Hysteresis
Dependence of viscosity/shear stress on shear rate: Newtonian fluids are fluids where the
shear rate does not have an effect on the shear stress or on the viscosity. As you increase the
shear rate the stress increases linearly so the viscosity will be constant.
Peanut butter is shear thickening.
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