Ice cream Flashcards
Characteristics of fat globules in ice cream
Partially coalesced globules and clumps
5-80 microns
Discrete phases in the serum or stabilising air cells
Used for aeration, retention and meltdown properties
What is in the serum phase of ice cream?
Water containing dissolved sugars, salts, proteins and stabilisers
What happens to the concentration of components after freezing?
Increases due to ice crystal formation
How does serum phase hold the ice cream structure together?
By interacting with other phases
How does serum phase prevent phase separation?
Reducing the growth of ice crystals
What is the perfect range for the size of ice crystals for a smooth ice cream?
30-50 microns
How large are air cells in ice cream?
20-25 microns
What are air cells stabilised by?
Destabilised fat globules
Milk protein
Viscosity in the serum phase
Why is the mixing stage important?
To disperse and hydrate ingredients
What is the step after mixing?
Pasteurisation at 80C for 30 seconds
Why is pasteurisation of ice cream important?
Destroy pathogens
Melt fat
Solubilise solids
What is the step after pasteurisation?
Homogenisation
Why is homogenisation important?
Disrupts phases causing droplet deformation, emulsifier adsorption and droplet collision
What is the role of emulsifiers in ice cream?
Allow milk membrane to coat the droplets as surface area has increased
What step is after homogenisation?
Cooling at <5C for 4-24 hours
Why is fat crystallisation important during cooling?
Fat destabilisation
What is fat destabilisation?
Rearrangement of milk fat globule interface with surfactants displacing proteins
What are crystalline fat globules formed by in the cooling stage?
Casein micelles in a solution of sugar, salt, whey and stabilisers
What is used for the cooling phase?
Scraped surface heat exchanger (SSHE)
What occurs in the SSHE?
Air is injected
Air cells are formed but reduce during whipping
Air cell size reduction is affected by viscosity
How does the SSHE limit the coalescence of globules?
Destabilisation of emulsion droplets and crystalline fat globules
How is the stability of fat globules reduced during cooling?
Displacement of proteins from the fat globule interface
What do partially coalesced fat globules do during cooling?
Stabilise air bubbles and form a network in the serum phase
What is hardening?
Process after cooling to reduce temperature from -6 to -18
What occurs during hardening?
Static cooling causes growth of ice crystals and change in air cell size
What causes change in air cell size during hardening?
Disproportionation, coalescence and drainage
What are colligative properties?
Properties that depend on number of solute particles
What are non-colligative properties?
Properties that depend on identity of dissolved species and solvent
How do solutes effect freezing?
Makes ice cream harder to freeze as the liquid is less ordered
What does temperature abuse cause?
Ice crystal and air cell changes
Loss of volume
Lactose crystallisation (sandy texture)
Why is temperature increase a problem?
Ice melts and diffuses in serum phase and drains through the product
What is meltdown rate?
Mass that drips through the product
What is meltdown rate affected by?
Overrun
Air cell stability
Fat destabilisation
Ice crystal size
Viscosity of serum phase
What increases recrystallisation?
Initial size
Insufficient freezing
What decreases recrystallisation?
Fat globule network
Ingredients with WHC
Serum phase viscosity
Proteins preventing water molecule exchange
How does ice cream shrink?
Loss of air cells
Formation of channels
Temperature fluctuations
