Ice cream

Question 1

Characteristics of fat globules in ice cream

Answer 1

Partially coalesced globules and clumps
5-80 microns
Discrete phases in the serum or stabilising air cells
Used for aeration, retention and meltdown properties

Question 2

What is in the serum phase of ice cream?

Answer 2

Water containing dissolved sugars, salts, proteins and stabilisers

Question 3

What happens to the concentration of components after freezing?

Answer 3

Increases due to ice crystal formation

Question 4

How does serum phase hold the ice cream structure together?

Answer 4

By interacting with other phases

Question 5

How does serum phase prevent phase separation?

Answer 5

Reducing the growth of ice crystals

Question 6

What is the perfect range for the size of ice crystals for a smooth ice cream?

Answer 6

30-50 microns

Question 7

How large are air cells in ice cream?

Answer 7

20-25 microns

Question 8

What are air cells stabilised by?

Answer 8

Destabilised fat globules
Milk protein
Viscosity in the serum phase

Question 9

Why is the mixing stage important?

Answer 9

To disperse and hydrate ingredients

Question 10

What is the step after mixing?

Answer 10

Pasteurisation at 80C for 30 seconds

Question 11

Why is pasteurisation of ice cream important?

Answer 11

Destroy pathogens
Melt fat
Solubilise solids

Question 12

What is the step after pasteurisation?

Answer 12

Homogenisation

Question 13

Why is homogenisation important?

Answer 13

Disrupts phases causing droplet deformation, emulsifier adsorption and droplet collision

Question 14

What is the role of emulsifiers in ice cream?

Answer 14

Allow milk membrane to coat the droplets as surface area has increased

Question 15

What step is after homogenisation?

Answer 15

Cooling at <5C for 4-24 hours

Question 16

Why is fat crystallisation important during cooling?

Answer 16

Fat destabilisation

Question 17

What is fat destabilisation?

Answer 17

Rearrangement of milk fat globule interface with surfactants displacing proteins

Question 18

What are crystalline fat globules formed by in the cooling stage?

Answer 18

Casein micelles in a solution of sugar, salt, whey and stabilisers

Question 19

What is used for the cooling phase?

Answer 19

Scraped surface heat exchanger (SSHE)

Question 20

What occurs in the SSHE?

Answer 20

Air is injected
Air cells are formed but reduce during whipping
Air cell size reduction is affected by viscosity

Question 21

How does the SSHE limit the coalescence of globules?

Answer 21

Destabilisation of emulsion droplets and crystalline fat globules

Question 22

How is the stability of fat globules reduced during cooling?

Answer 22

Displacement of proteins from the fat globule interface

Question 23

What do partially coalesced fat globules do during cooling?

Answer 23

Stabilise air bubbles and form a network in the serum phase

Question 24

What is hardening?

Answer 24

Process after cooling to reduce temperature from -6 to -18

Question 25

What occurs during hardening?

Answer 25

Static cooling causes growth of ice crystals and change in air cell size

Question 26

What causes change in air cell size during hardening?

Answer 26

Disproportionation, coalescence and drainage

Question 27

What are colligative properties?

Answer 27

Properties that depend on number of solute particles

Question 28

What are non-colligative properties?

Answer 28

Properties that depend on identity of dissolved species and solvent

Question 29

How do solutes effect freezing?

Answer 29

Makes ice cream harder to freeze as the liquid is less ordered

Question 30

What does temperature abuse cause?

Answer 30

Ice crystal and air cell changes Loss of volume Lactose crystallisation (sandy texture)

Question 31

Why is temperature increase a problem?

Answer 31

Ice melts and diffuses in serum phase and drains through the product

Question 32

What is meltdown rate?

Answer 32

Mass that drips through the product

Question 33

What is meltdown rate affected by?

Answer 33

Overrun Air cell stability Fat destabilisation Ice crystal size Viscosity of serum phase

Question 34

What increases recrystallisation?

Answer 34

Initial size Insufficient freezing

Question 35

What decreases recrystallisation?

Answer 35

Fat globule network Ingredients with WHC Serum phase viscosity Proteins preventing water molecule exchange

Question 36

How does ice cream shrink?

Answer 36

Loss of air cells Formation of channels Temperature fluctuations