| What are the simple ingredients in ice cream, and then the more in-depth | SIMPLE: Ice, cream, flavours, sugar and air
IN-DEPTH: proteins, fat, emulsifier, sugar, stabiliser, inclusions, flavour and water |
| What % of ice cream is air | 50%. Less air = more premium |
| What does sugar do to the product | Lowers the freezing temperature. More sugar = lower freezing temperature (freezing point depression) |
| Define matrix phase | Holds the ice phase together. Consists of protein, sugars and stabilisers |
| List the composition of ice cream in terms of volume and energy contribution | See image |
| What is the point of proteins inside air bubbles | Structure-in-structure which stabilises the product |
| What is the manufacturing process for ice cream | Mixing (room temperature) -> homogenisation (high pressure) -> Pasteurisation -> Freezing (put air in) -> Extrusion (mould asap) -> Hardening (blast freezer) -> Coating -> Cold store -> Distribution |
| How does the ice cream freezer work | As a surface heat exchanger with a dasher inside a hollow cylinder |
| Why are foams (such as ice cream) annoying | Unstable due to density difference. They are like emulsions but just with different densities |
| What are the name of particles of which stabilise fat droplets in ice cream? | Pickering particles |
| What is the vital role for fat and proteins | Hardening stage when the temperature distribution fluctuates. Proteins stabilise and fats crystallize |
| What are the three foam destabilisation mechanisms (want to avoid these) | Disproportionation, coalescence and creaming of bubbles and serum drainage |
| What are some issues within the ice cream process | Aeration & freezing (pressure drop, coalescence) -> extrusion (low viscosity, disproportionation) -> Harden and store (temperature, abuse and coalescence) -> Transportation (melting) ->consume |
| Why do bubbles expand on extrusion | Due to Laplace pressure difference |
| What are some problems when transporting ice cream | As altitude changes, so does pressure, thus changing volume as P1V1 = P2V2 |
| What are some solution to transporting ice cream | Pressurized transport (expensive)
Leave space in tubs (waste of plastic, consumer wont be happy)
Put in less air (destroys product)
Find a different route (expensive with fuel)
Engineer microstructure to be stable to pressure changes |
| What two things do you want built in stability into the microstructure to ensure the product is stable? | Build in stability to coalescence and disproportionation |
| What is the difference of protein at the surface compared to protein and fat at the surface | Just protein: low surface elasticity and viscosity gives poor stability
Protein and Fat: better bubble stability. High surface elasticity and viscosity and predict improved stability |
| What are the three methods to make an emulsion stable at the interface | Add either proteins, small molecules or mix of both |
| What is emulsion stability related to | Type of adsorbed material, where proteins form very stable emulsions. Ideal level of protein can be found experimentally |
| What are some technical challenges with ice cream (overall challenges with the product) | Make and keep small air bubbles, even through storage abuse. Control bubble stability as matrix is changed. Also, to prevent coalescence and disproportionation |
| How do you reduce coalescence | Thicker interfacial area, high solid fat content and gelled continuous phase |
| Define disproportionation | Solubility difference in smaller bubbles and larger bubbles, where the smaller bubbles dissolves into the larger bubbles |
| How do you reduce disproportionation | Attach proteins, crystals, monoglycerides, Pickering particles or a mixture of proteins and monoglycerides to the bubbles surface |
| Stability of air phase is caused by trapping the structure at what temperature | -18 degrees celsius |
| Define ageing | Sometimes occurs between pasteurisation and freezing. Allows the product to sit and rest or low speed stirring and cooling at 5 degrees Celsius. Aim is crystallisation of fats, hydration and protein rearrangement |
