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I c e - C r e a m

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  1. Ice- Cream Food Facts & FallaciesYSCN0006

  2. I scream You scream We all scream for ice-cream

  3. What is ice-cream? 1 • Cool • Smooth • Yummy

  4. What is ice-cream? 2 • Water • Fat • Carbohydrate • Protein • Air

  5. What is ice-cream? 3 • Solid (at low temp) • Liquid (at room temp) • A colloid • Emulsion • Frozen foam

  6. 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

  7. Milk ~ Fat in water emulsion

  8. Butter ~ Water in fat emulsion

  9. Ice-cream

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

  11. Making ice cream • Ingredients • Mixing • Freezing • Hardening

  12. 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

  13. 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

  14. After homogenisation • Addition of liquid flavours • Colouring • Fruit puree

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

  16. The Importance of Air - 40°C - 5°C

  17. Not Enough Air • a solid lump of ice? • Too cold • Too hard • Too rich, percentage fat too high

  18. Too Much Air • Dry texture • Melts too quickly • Correct quantity around 50% of volume • = overrunof 100 • overrun is used to control the texture of ice-cream

  19. 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

  20. 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

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

  22. 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

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

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

  25. 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)

  26. 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

  27. Dr Ramsden’s special HKU chocolate ice -cream • Chocolate 60g • Milk 200ml • Cream 400ml • Sugar 150g • Vanilla 10ml • Egg yolk x 3

  28. 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