Ice- CreamFood Facts & Fallacies YSCN0006

I scream You scream We all scream for ice-cream

What is ice-cream? 1CoolSmoothYummy

What is ice-cream? 2WaterFatCarbohydrateProteinAir

What is ice-cream? 3Solid (at low temp)Liquid (at room temp)A colloidEmulsionFrozen foam

What is a Colloid ?Physical statesSolids, Liquids, Gases and.Stable mixtures of them are colloidsEmulsion, solid dispersed in a liquidFoam, gas dispersed in a liquid

Milk ~ Fat in water emulsion

Butter ~ Water in fat emulsion

Ice-cream

Sizesdissolved sugars, polysaccharides, proteinsfat globules 1 to 5 mice crystals 30 to 50 mair bubbles 50 to 100 m

Making ice creamIngredientsMixingFreezingHardening

IngredientsSucrose 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-creamMixing of ingredients and homogenisation to give small fat globules.Pasteurisation to cook and sterilise the mixCooling, allows crystallisation of fat in globules

After homogenisationAddition of liquid flavoursColouringFruit puree

FreezingUses a scraped barrel freezerSimultaneous beating and freezingBeating to destabilize fat emulsionincorporate air

The Importance of Air- 40C- 5C

Not Enough Aira solid lump of ice?Too coldToo hardToo rich, percentage fat too high

Too Much AirDry textureMelts too quicklyCorrect quantity around 50% of volume= overrun of 100overrun is used to control the texture of ice-cream

After Freezingabout 50% water frozenSot texture =Soft serve ice-cream as used for conesParticulate addition, eg. nuts, biscuit crumbs, chocolate chipsPackaging

Freeze concentrationdissolved solutes depress the freezing point of a liquidthe higher the concentration the greater the depressionas the ice-cream water freezes the concentration of sugars increaseseven at very low temperatures there will be a small amount of unfrozen water present

HardeningContinuous blast freezer or batch freezer-40 Cremaining water frozenice-cream stable if kept below -25C

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 & StabilisersEmulsifiershelp fat globule breakdownessential to stabilise air bubblesStabilisersreduce ice-crystal growth

Sugar crystalsformation of lactose crystals detectable as gritty sandiness in textureavoided by fast freezing and rapid formation of glass

Other IcesSorbet & water ices (no milk fat, high fruit)Sherbets (added citric acid)Frozen yoghourt (fermented milk solids)Ice-milk (3-5% milk fat)

Ice Bars & NoveltiesFormed by moulding or extrusionMoulding requires a stick!Centre filling possible with moulded barsAfter freezing products can be coated and enrobed

Dr Ramsdens special HKU chocolate ice -creamChocolate 60gMilk200mlCream400mlSugar150gVanilla10mlEgg yolk x 3

Preparation methodmelt chocolate & mix with milkmix egg yolks with sugaradd cream and vanilla to chocolate milk and bring to boilallow to cool & then add egg sugarmix at low heat for 15 min4C for 4 hoursfreeze for 30 minharden at 30C 12 h