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Advanced mulecular gastronomy summary
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ADVANCED MOLECULAR GASTRONOMY SUMMARYIce cream Ice-cream divided in 2: water and total solids
Types of ice cream
- Dairy ice cream (milk or cream)
- Non-dairy ice cream (vegetable fat)
- Gelato (custard based ice cream) (used to consist
eggs in Italy)
- Frozen yogurt (contains lots of sugar instead fat)
- Sorbet (fruit based, no fat or milk)
- Sherbet (similar to sorbet but with some milk)
- Water ice, frozen sugar syrup
- Fruit ice (similar to water ice, but with real fruit)
Ice cream structure
Ice creams starts with a emulsion and in the frozen version it is a foam that contains air bubbles and
ice crystals trapped in the continuous phase (serum phase) with sugar in it. The fat is mostly
surrounding the air bubbles. 60% of the water in ice cream (30% ice crystals) is frozen and only 1/3 of
the water (15% unfrozen matrix/serum phase) is available for the sugar to dissolve in.
Function total solids:
Milk protein → caseins / whey: provide flavour and have
emulsifying properties
Sugar → control amount of ice and make it sweet
Fat → stabilize the foam, creamy texture, slow down
melt, fat-soluble flavours
Emulsifiers and Stabilizers → increase foam and increase shelf-life
Four microstructural elements:
Ice → Amount of ice is determined by the freezing point depression. Determines hardness, coldness,
melting
Matrix / serum phase → Solution of sugars, stabilizers and milk proteins. As water freezes, the
concentration of these ingredients increases
Fat → Fat is present as partially coalesced fat increases the stability of the air bubbles
Air → Sizes of the air bubbles determine sensory properties and influence shelf-life
Freeze depression
Limiting the crystallization of water by adding sugar to
soften the ice cream. Addition of sugar lowers the
freezing temperature. Changes the melting/freezing
temperature of ice.
Chemical potential water = chemical potential of ice:
Freezing point depression formula →
Freezing point is based on the amount of 1 kg of liquids!
Salt is much more effective for freeze depression because salt molecules are smaller.
1) Water starts to freeze at TF (-2ºC)
2) Ice crystals push out the sugar
- sugar concentration in the serum phase will increase
- ΔTF of the serum phase will increase again
3) Stops crystallizing when the TF is the same as the temperature of the freezer (-18ºC)
- Concentration of sugar is +/- 65%, which is a supersaturated state
- Glass solid, solution is very viscous and holds the ice-cream together (need it)
,The 65 % sugar solution (serum) is now a very viscous syrup in rubber/glassy state, it is
the “glue” that holds everything together and provides “body” to the ice cream that
holds the air bubbles in place.
Freezing depression is dependent on the type of sugar (the size of the sugar molecules)
(monosaccharide) glucose is smaller than (disaccharide) sucrose → larger freezing
point depression.
Calculating the mass of ice & the %sugar in the serum
So 470 grams of the total 700 grams of water turned into
ice. That means that 230 grams of water remains in the
serum with 300 grams of sugar → so the serum has a sugar
content of 57%.
Calculating the %ice as a function of T with known msolutes
Pure water: Tm = 0 ºC = 273 K
For ice: Tm = ΔTF = -2 / -3 ºC = 270 – 271 K
Calculating the msolutes as a function of T with known %ice
Sweetness of sugar
Not only influences the type of sugar the freezing point
depression but also the sweetness of the ice-cream. When
replacing a sugar for another sugar with a lower sweetness
and a higher freezing point depression → add less because of
higher freezing point depression → less sweet → lower
sweetening power → even less sweet. Better replacing the
sugar with another sugar with a higher freezing point
depression (smaller Mw!) and a higher sweetness.
➔ Combination of sugars controls the amount of ice and sweetness
Formation of ice crystals during freezing
Formation of ice crystals is a combination of energy
gain (from making water into ice) and energy cost
(making interface between ice and water). So the
energy is dependent on whether the ice crystals
grow or melt. Till a certain crystal radius the crystal
want to melt because it cost energy. But from radius
rc (critical size) the crystal gains energy by growing
even more. When rc is reached → crystal will grow!
Lower half of the diagram is negative side → is
actually positive → energy gain
Low melting temperature → smaller critical radius
Larger difference in temp → smaller critical radius G = gibs energy
y = interfacial tension between
ice and water
u = change in chemical potential
H = enthalpy of freezing
,When rc is reached → crystal will grow. But you want the ice-crystals to be small enough so that the
ice-cream will be smooth.
Small critical radius → many small crystals
Size/amount of crystals is related to mouthfeel:
Large critical radius → few large crystals
- Iciness (size)
T determines partly the critical size.
- Hardness (amount/size) Effect of freezing will influence crystal size
- Smoothness (size) and growth
- Coldness (melting profile, size/amount)
Size/amount of crystals: Can be controlled by
- Freeze depression (additives: sugar, alcohol, salt, etc)
- temperature difference ( freezer, liquid nitrogen)
→ the bigger the dT, the smaller the crystal size
Milk (fat and proteins)
During freezing: freeze concentration drives fat particles together →
partial fat destabilization → partial coalescence. These agglomerated
fat particles form a layer around the air bubbles and stabilizes it. The
agglomerated fat particles can also form a network between different
air bubbles, this contributes to the hardness of the ice-cream and limits
the collapse of the ice-cream by melting of the ice.
Whey proteins sit at the interface so also have a stabilising effect.
Casein micelles can attach to fat globules, this partly prevents
agglomeration of the fat particles because it prevents fat surfaces to
come together → having casein in ice-cream is not wanted!
Emulsifiers
This is why emulsifiers are added. The surfactant compete with casein micelles to stabilize the fat
globules (kick of casein from the fat surface). Surfactant is much smaller than the micelle so fat
globules can come together much more → inducing fat coalescence
➔ Destabilizing effect for fat → Stabilizing effect for air bubbles!
The whey proteins at the interface stabilize and prevent collapse of the air bubbles → have to be
available to form a network around the air. But if the surfactants also kick of the whey proteins, you
increase the coalescence of the air bubbles (because the surfactants are much smaller)
➔ Destabilizing effect for air bubbles → Collapse of ice cream
You want enough emulsifier to chase away the casein of the fat but not too much that it kicks of the
whey proteins of the air interface.
(in sorbet (no fat/proteins) the air bubbles are only stabilized by the viscosity of surrounding serum)
Stabilizers
As stabilizers, mostly different polysaccharides are used.
Polysaccharides have a positive effect on the size of ice crystals (small)
Role / function:
- Water-binding ability → Free water decreases: less ice
- Create smoothness in texture and eating → Viscosity increase
- Reduction of meltdown
- Slowing down moisture migration
- Masking detection of ice crystals
- Incorporation of air
Negative effect of stabilizers:
They bind water, so even less water available for the sugar, increases the sugar content. Max sugar
content reached and sugar crystallizes out of solution “white spots” .
Phase separation of polysaccharide and protein due to depletion interactions. Areas with different
water binding capacity → inhomogeneous in structure and different crystallization behaviour in mix.
, Effect of time and temp on ice crystals
Recrystallization: Increase temp during storage melts away the smallest ice-crystals. Recrystallisation
when decreasing temp again, water binds to already existing crystals (making them larger)
Increase in ice particle Size → effect on mouth feel → > 100 micron: can be detected in the mouth as
icy and gritty.
Accretion: solid version of partial coalescence → touching ice
particles form a neck → grow into one crystal (happens over time)
Ostwald ripening: Solubility of a material is dependent on the
pressure: Smaller radius higher solubility → concentration gradient:
large droplets grow at the expense of the smaller ones.
Polysaccharides increase the viscosity and thereby decrease the
water migration rate (diffusion coefficient) and limits the Ostwald ripening rate.
Ice-structuring proteins (ISP)
Proteins that prevent ice-crystal growth. Protein sits on the ice-crystal and prevent
further growth of the ice-crystal. Protein gives a local freezing point depression.
Formula related to 3 interfacial tensions (protein-water = s-l) (protein-ice = s-s) (ice-
water = s-l)
Air
Air bubbles: 40 microns to 100 microns (softness, colour)
Pressure sensitive → lowering pressure means expanding of the air bubbles → change for
coalescence and air can escape and ice-cream collapses
Coalescence: touching of two droplets (neck) → one air channel of multiple touching droplets.
Prevented by strong interface → adsorption of fat droplets (create strong interface)
Disproportionation: large droplets grow at the expense of the smaller ones (pressure gradient)
Making of ice-cream
- Mix preparation
Blend, disperse and hydrate
Heated at 65 ºC to prevent denaturation of protein
Homogenize to decrease the size of fat crystals
- Aging
Cooled to 4 ºC.
Proteins are replaced by emulsifiers
Fat droplets will crystallize
- Freezing o Subject mix to high shear
Microstructure of the ice cream is determined o Beating shears and breaks bubbles into smaller ones
Simultaneous freezing and mixing o Causes fat droplets to coalesce
Scraper has three functions: →
Freezing step determines: Size of crystals & Size of air bubbles & overrun: ratio of V gas/V liquid
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