Ice- Cream

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					Ice- Cream
Food Facts & Fallacies
      YSCN0006
          I scream
        You scream
We all scream for ice-cream
What is ice-cream? 1
 • Cool
 • Smooth
 • Yummy
      What is ice-cream? 2
•   Water
•   Fat
•   Carbohydrate
•   Protein
•   Air
      What is ice-cream? 3
•   Solid (at low temp)
•   Liquid (at room temp)
•   A colloid
•   Emulsion
•   Frozen foam
            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
Milk ~ Fat in water emulsion
Butter ~ Water in fat emulsion
Ice-cream
                     Sizes
•   dissolved sugars, polysaccharides, proteins
•   fat globules 1 to 5 µm
•   ice crystals 30 to 50 µm
•   air bubbles 50 to 100 µm
            Making ice cream
•   Ingredients
•   Mixing
•   Freezing
•   Hardening
                 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
           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
 After homogenisation
• Addition of liquid flavours
• Colouring
• Fruit puree
                  Freezing
• Uses a scraped barrel freezer
• Simultaneous beating and freezing
• Beating to
   destabilize fat emulsion
   incorporate air
        The Importance of Air

- 5°C                           - 40°C
              Not Enough Air
•   a solid lump of ice?
•   Too cold
•   Too hard
•   Too rich, percentage fat too high
               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
             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
         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
                  Hardening
•   Continuous blast freezer or batch freezer
•   -40 °C
•   remaining water frozen
•   ice-cream stable if kept below -25°C
                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
      Emulsifiers & Stabilisers
• Emulsifiers
  – help fat globule breakdown
  – essential to stabilise air bubbles
• Stabilisers
  – reduce ice-crystal growth
             Sugar crystals
• formation of lactose crystals detectable as
  gritty sandiness in texture
• avoided by fast freezing and rapid
  formation of glass
                  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)
          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
Dr Ramsden’s special HKU
   chocolate ice -cream
  •   Chocolate 60g
  •   Milk    200ml
  •   Cream 400ml
  •   Sugar 150g
  •   Vanilla 10ml
  •   Egg yolk x 3
        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
• 4°C for 4 hours
• freeze for 30 min
• harden at 30°C 12 h

				
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