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I c e - C r e a m. 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 - PowerPoint PPT Presentation
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Ice- Cream
Food Facts & FallaciesYSCN0006
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
- 40°C- 5°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