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
Sizes
• dissolved sugars, polysaccharides, proteins
• fat globules 1 to 5 µm
• ice crystals 30 to 50 µm
• air bubbles 50 to 100 µm
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
Freezing
• Uses a scraped barrel freezer
• Simultaneous beating and freezing
• Beating to destabilize fat emulsion incorporate air
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
Top Related