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