Ice- Cream

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Ice- Cream

• Food Facts FallaciesYSCN0006

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• I scream
• You scream
• We all scream for ice-cream

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What is ice-cream? 1

• Cool
• Smooth
• Yummy

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What is ice-cream? 2

• Water
• Fat
• Carbohydrate
• Protein
• Air

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What is ice-cream? 3

• Solid (at low temp)
• Liquid (at room temp)
• A colloid
• Emulsion
• Frozen foam

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What is a Colloid ?

• Physical states
• Solids, Liquids, Gases and.
• Stable mixtures of them are colloids
• Emulsion, solid dispersed in a liquid
• Foam, gas dispersed in a liquid

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Milk Fat in water emulsion
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Butter Water in fat emulsion
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Ice-cream
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Sizes

• dissolved sugars, polysaccharides, proteins
• fat globules 1 to 5 µm
• ice crystals 30 to 50 µm
• air bubbles 50 to 100 µm

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Making ice cream

• Ingredients
• Mixing
• Freezing
• Hardening

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Ingredients

• Sucrose 15
• Milk fat 15 (legal min. 10)
• Non-fat milk solids 10 (lactose casein)
• Corn syrup 5 (fructose dextrins)
• Stabilisers 0.4 (polysaccharides)
• Emulsifier 0.2 (mono or di-glycerides)
• Water

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Making ice-cream

• Mixing of ingredients and homogenisation to give
  small fat globules.
• Pasteurisation to cook and sterilise the mix
• Cooling, allows crystallisation of fat in globules

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After homogenisation

• Addition of liquid flavours
• Colouring
• Fruit puree

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Freezing

• Uses a scraped barrel freezer
• Simultaneous beating and freezing
• Beating to
• destabilize fat emulsion
• incorporate air

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The Importance of Air
- 40C
- 5C
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Not Enough Air

• a solid lump of ice?
• Too cold
• Too hard
• Too rich, percentage fat too high

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Too Much Air

• Dry texture
• Melts too quickly
• Correct quantity around 50 of volume
• overrun of 100
• overrun is used to control the texture of
  ice-cream

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After Freezing

• about 50 water frozen
• Sot texture
• Soft serve ice-cream as used for cones
• Particulate addition, eg. nuts, biscuit crumbs,
  chocolate chips
• Packaging

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Freeze concentration

• dissolved solutes depress the freezing point of a
  liquid
• the higher the concentration the greater the
  depression
• as the ice-cream water freezes the concentration
  of sugars increases
• even at very low temperatures there will be a
  small amount of unfrozen water present

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Hardening

• Continuous blast freezer or batch freezer
• -40 C
• remaining water frozen
• ice-cream stable if kept below -25C

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Ice crystals

• essential to stabilise air bubbles
• too big give a gritty texture
• small crystals formed by
• good nucleation
• rapid freezing
• ice crystals grow if temperature fluctuates

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Emulsifiers Stabilisers

• Emulsifiers
• help fat globule breakdown
• essential to stabilise air bubbles
• Stabilisers
• reduce ice-crystal growth

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Sugar crystals

• formation of lactose crystals detectable as
  gritty sandiness in texture
• avoided by fast freezing and rapid formation of
  glass

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Other Ices

• Sorbet water ices (no milk fat, high fruit)
• Sherbets (added citric acid)
• Frozen yoghourt (fermented milk solids)
• Ice-milk (3-5 milk fat)

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Ice Bars Novelties

• Formed by moulding or extrusion
• Moulding requires a stick!
• Centre filling possible with moulded bars
• After freezing products can be coated and enrobed

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Dr Ramsdens special HKU chocolate ice -cream

• Chocolate 60g
• Milk 200ml
• Cream 400ml
• Sugar 150g
• Vanilla 10ml
• Egg yolk x 3

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Preparation method

• melt chocolate mix with milk
• mix egg yolks with sugar
• add cream and vanilla to chocolate milk and bring
  to boil
• allow to cool then add egg sugar
• mix at low heat for 15 min
• 4C for 4 hours
• freeze for 30 min
• harden at 30C 12 h