food physics
general introduction
recipe is a function of variables (time, temperature, ingredient, details of process)
viscosity of batter determines success of baking cake
precision is a measure of quality/completeness
recent developments
technique = process/combination of processes that makes a product edible or induces
another type of transition
concept = the basic idea behind the dish/recipe
- carpaccio: thin slices of meat
- salad: mix of greens
spherification:
- if the liquid contains calcium > alginate bath
- if not > add alginate to liquid > calcium bath
adaptation = 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
minimization = obtain a maximum attractiveness with a minimum of ingredients, for instance
present one ingredient in different forms and textures
ingredients originating in food science/technology (hydrocolloids, enzymes and emulsifiers)
are powerful tools to (help) produce dishes that are otherwise impossible to make
structured approach
basics of cooking
cooking: transfer of energy from flame to pan
temperature = measure for the average motion of the molecules of a material
sensory properties of cooked food are result of heat-induced physical and chemical changes
- denaturation, hydrolysis
,heat transfer mechanisms
- radiation: transfer heat by means of emission/absorption of electromagnetic radiation
- no physical contact between energy source and food
- infrared (electric ovens): heat absorption on surface
- color of food and distance play both important role in heating
- microwave (microwave ovens): deep penetration of heat
- conduction: transfer heat between objects in physical contact
- braising, cooking in salt crust
- Fourier equation
- thermal diffusivity:
- quantity of heat transmitted through a unit thickness in a direction
normal to a surface of unit area, due to a unit temperature gradient
- heat capacity = amount of heat needed to raise the temperature by a
specified quantity and depends on chemical composition (low protein
content and/or high fat content = low heat capacity)
- convection: transfer heat between object and its environment due to fluid motion
- boiling, deep-frying, hot air/baking ovens
- phase change: transfer heat because of evaporation/condensation
- steaming
heat transport depends on specific heat capacity, density, thermal conductivity and
mechanism of heat transfer
water:
- high surface tension and specific heat capacity
- high boiling and low freezing point
- expands when freezing
- good solvent for polar compounds
- in water containing food, the temperature cannot be higher than 100 degrees celsius
until water has evaporated (otherwise food experiences temperatures lower than set)
- water subtracts heat when evaporating
- steam releases heat when condensing
- ice subtracts heat when melting
cooking techniques: grilling, broiling, roasting, panfrying, sauteing, stir-frying, boiling,
steaming, stewing, baking, deep frying, microwaves, sous-vide
boiling:
- rice/pasta: rolling boiling (small objects and fast heating (large bubbles))
- fish: simmer (slow heating)
deep-frying:
- steam bubbles when putting product into oil (from water on/in first millimeters of
surface)
cooking sous-vide:
- working with plastic > not very healthy (microplastics)
- 2 step preparation: first in water bath to cook the meat and then fry/bake to create
crust
, - leave product too long in waterbath at 55 degrees celsius: bacteria can easily grow &
some enzymes are very active at this temperature and meat > sort of mouse; a
digested piece of meat
recap food physics
texture = whole structural/mechanical properties of food products as being conceived by
humans by touch/eyes/ears
mechanical properties: elasticity, viscosity, fracture stress, yield stress
- viscous flow (liquids)
- elastic deformation (solids)
- viscoelastic behavior (most food products)
stress (σ): force per unit area applied to material
strain (ε): relative deformation of material
shear modulation: modulus of rigidity and stiffness
hardness: force needed to apply to fall apart
structure and its rearrangements are linked to: Newtonian, shear thinning, shear thickening,
bingham flow, plastic flow, thixotropy, anti-thixotropy and hysteresis
- newtonian liquid: no interactions between particles (too far from each other) or just no
structural elements (to interact with)
- shear thinning (starch, mayo): viscosity decreases under shear strain, more order >
easier flow
- shear thickening (peanutbutter): viscosity increases under shear strain, increased
friction/chaos
- plastic flow: plastic material behaving like shear thinning material
- bingham flow (ketchup): newtonian liquid with yield stress
, - (anti-)thixotropy: related to time-dependency than stress-dependency
- anti-thixotropy isn’t observed in food products
- thixotropy (yogurt): time-dependent shear thinning
- hysteresis: at constant water activity and temperature, a food adsorbs a smaller
amount of water during adsorption than subsequent desorption
tribology: measurement of frictional properties
- rotating rubber disc & pin with rubber ring (that is lowered)
psycho-rheology studies how consumer perceives characteristics of product and its quality
eating process: first impression outside mouth > first impression inside mouth > chewing
properties > impressions after swallowing
surface tension = tendency of materials to reduce the surface area
- higher temperature > lower surface tension
proteins (as surfactants)
- at interfaces change their conformation and form an elastic gel
- change back their configuration to go off (low chance compared to other surfactants)
Laplace pressure: balance energy of volume term with energy of area term
- lower surface tension > lower difference in Laplace pressure
instability in emulsions/foams:
general introduction
recipe is a function of variables (time, temperature, ingredient, details of process)
viscosity of batter determines success of baking cake
precision is a measure of quality/completeness
recent developments
technique = process/combination of processes that makes a product edible or induces
another type of transition
concept = the basic idea behind the dish/recipe
- carpaccio: thin slices of meat
- salad: mix of greens
spherification:
- if the liquid contains calcium > alginate bath
- if not > add alginate to liquid > calcium bath
adaptation = 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
minimization = obtain a maximum attractiveness with a minimum of ingredients, for instance
present one ingredient in different forms and textures
ingredients originating in food science/technology (hydrocolloids, enzymes and emulsifiers)
are powerful tools to (help) produce dishes that are otherwise impossible to make
structured approach
basics of cooking
cooking: transfer of energy from flame to pan
temperature = measure for the average motion of the molecules of a material
sensory properties of cooked food are result of heat-induced physical and chemical changes
- denaturation, hydrolysis
,heat transfer mechanisms
- radiation: transfer heat by means of emission/absorption of electromagnetic radiation
- no physical contact between energy source and food
- infrared (electric ovens): heat absorption on surface
- color of food and distance play both important role in heating
- microwave (microwave ovens): deep penetration of heat
- conduction: transfer heat between objects in physical contact
- braising, cooking in salt crust
- Fourier equation
- thermal diffusivity:
- quantity of heat transmitted through a unit thickness in a direction
normal to a surface of unit area, due to a unit temperature gradient
- heat capacity = amount of heat needed to raise the temperature by a
specified quantity and depends on chemical composition (low protein
content and/or high fat content = low heat capacity)
- convection: transfer heat between object and its environment due to fluid motion
- boiling, deep-frying, hot air/baking ovens
- phase change: transfer heat because of evaporation/condensation
- steaming
heat transport depends on specific heat capacity, density, thermal conductivity and
mechanism of heat transfer
water:
- high surface tension and specific heat capacity
- high boiling and low freezing point
- expands when freezing
- good solvent for polar compounds
- in water containing food, the temperature cannot be higher than 100 degrees celsius
until water has evaporated (otherwise food experiences temperatures lower than set)
- water subtracts heat when evaporating
- steam releases heat when condensing
- ice subtracts heat when melting
cooking techniques: grilling, broiling, roasting, panfrying, sauteing, stir-frying, boiling,
steaming, stewing, baking, deep frying, microwaves, sous-vide
boiling:
- rice/pasta: rolling boiling (small objects and fast heating (large bubbles))
- fish: simmer (slow heating)
deep-frying:
- steam bubbles when putting product into oil (from water on/in first millimeters of
surface)
cooking sous-vide:
- working with plastic > not very healthy (microplastics)
- 2 step preparation: first in water bath to cook the meat and then fry/bake to create
crust
, - leave product too long in waterbath at 55 degrees celsius: bacteria can easily grow &
some enzymes are very active at this temperature and meat > sort of mouse; a
digested piece of meat
recap food physics
texture = whole structural/mechanical properties of food products as being conceived by
humans by touch/eyes/ears
mechanical properties: elasticity, viscosity, fracture stress, yield stress
- viscous flow (liquids)
- elastic deformation (solids)
- viscoelastic behavior (most food products)
stress (σ): force per unit area applied to material
strain (ε): relative deformation of material
shear modulation: modulus of rigidity and stiffness
hardness: force needed to apply to fall apart
structure and its rearrangements are linked to: Newtonian, shear thinning, shear thickening,
bingham flow, plastic flow, thixotropy, anti-thixotropy and hysteresis
- newtonian liquid: no interactions between particles (too far from each other) or just no
structural elements (to interact with)
- shear thinning (starch, mayo): viscosity decreases under shear strain, more order >
easier flow
- shear thickening (peanutbutter): viscosity increases under shear strain, increased
friction/chaos
- plastic flow: plastic material behaving like shear thinning material
- bingham flow (ketchup): newtonian liquid with yield stress
, - (anti-)thixotropy: related to time-dependency than stress-dependency
- anti-thixotropy isn’t observed in food products
- thixotropy (yogurt): time-dependent shear thinning
- hysteresis: at constant water activity and temperature, a food adsorbs a smaller
amount of water during adsorption than subsequent desorption
tribology: measurement of frictional properties
- rotating rubber disc & pin with rubber ring (that is lowered)
psycho-rheology studies how consumer perceives characteristics of product and its quality
eating process: first impression outside mouth > first impression inside mouth > chewing
properties > impressions after swallowing
surface tension = tendency of materials to reduce the surface area
- higher temperature > lower surface tension
proteins (as surfactants)
- at interfaces change their conformation and form an elastic gel
- change back their configuration to go off (low chance compared to other surfactants)
Laplace pressure: balance energy of volume term with energy of area term
- lower surface tension > lower difference in Laplace pressure
instability in emulsions/foams:
