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 - 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 Milk200ml Cream400ml Sugar150g Vanilla10ml 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