Food Tech: Chapter 4 Flashcards
Describe the physical and sensory properties of goats milk
Goat’s milk is sweeter and whiter in colour than cow’s milk. Its nutritional composition is similar to cow’s milk
Describe the physical and sensory properties of cow’s milk
Cow’s milk is a white, opaque liquid which contains almost three times more protein than human milk
Describe the physical and sensory properties of sheep’s milk
Sheep’s milk has a much higher fat content than cow’s milk, providing almost twice the fat content. This high fat content gives it a sweeter and richer flavour and much whiter colour.
Name the nutrients found in milk
- protein
- fat
- carbohydrates (sugars, lactose)
- vitamins (vitamin A and D)
- minerals (calcium, phosphorus)
- water (87% water)
Name the dairy products made from milk
Liquid milk, concentrated (condensed) milk, powdered milk, buttermilk, milk proteins, yoghurt, cream, butter, ice-cream, cheese.
Describe pasteurisation
Pasteurisation destroys pathogenic or disease-causing bacteria and also extends the shelf life of milk. The milk is heated to 72 degrees for 15 seconds and the is cooled rapidly to 2 degrees.
Describe UHT (ultra high temperature)
UHT refers to processing milk at higher temperatures than for pasteurisation, but for a much shorter time, killing all bacteria in milk, including those that turn milk sour. The milk is heater to 135 degrees for 2-3 seconds. UHT milk can be stored for 3-6 months without refrigeration.
Describe homogenisation
The milk is forced through small nozzle-like openings or between closely position plates to break down fat globules and evenly distribute cream to create a smooth, creamy texture
What are the advantages of homogenising milk?
- uniform distribution of fat, so there is no cream layer
- more full-bodied flavour
- white, more appealing colour
- faster coagulation in the manufacture of cheese
Describe membrane technology
Membrane technology involves using a porous membrane or filter to separate the particles in a fluid. Two of the most commonly used forms or membrane technology in food production are ultrafiltration and reverse osmosis.
Describe ultrafiltration
Ultrafiltration is a form of membrane technology in which milk is pumped across a membrane to collect the protein and fat and some of the calcium molecules, but the water and lactose are allowed to pass through.
Describe reverse osmosis
Reverse osmosis is a form of membrane technology similar to ultrafiltration but the pores in the membrane are smaller and allow only water to pass through, leaving behind concentrated milk solids
Describe the primary processing of milk
- milking of cows
- collection of milk
- analysis
- membrane technology filtration
- pasteurisation
- homogenisation
- packaging or secondary processing
Describe the secondary processing of milk (production of cheese)
- curd formation
- syneresis (the curd is gently heated so it shrinks and toughens)
- milling (curd is cut into small, even sized pieces)
- salting
- moulding (cheese is pressed into shape)
- maturation (cheese is stored Ina cool environment to develop flavour and texture, the longer the sharper the flavour and crumblier texture)
- packaging and labelling
Define coagulation
Coagulation is a form of denaturation and occurs when there is a permanent change in the protein from a liquid into a thick mass as a result of heat, or the addition of acids.
Define denaturation
Denaturation describes a permanent structural change of the protein molecules in food. This can occur with the application of heat, mechanical action or the addition of acids.
What happens when you heat milk to 100degrees?
- Milk starts to boil at 100 degrees.
- The proteins present on the surface of the milk combine with the fat to form a skin.
- Milk boils over as a result of pressure of steam forcing its way through the skin.
What happens when you combines egg with milk?
- A custard mixture is formed.
- The consistency of custard depends on the proportion go eggs to milk. The more eggs than milk, the thicker it will be.
- The smooth texture is due to the gentle cooking, making sure the eggs coagulates or sets evenly within the milk at a temperature between 65-70 degrees.
- custards can be baked or cooked on a stove top
Why is a double boiler used to prepare a custard?
Cooking a custard in a water bath helps prevent the delicate mixtures from curdling or separating.
-If the custard is overheated, the proteins from the egg and milk begin to over-coagulate to form small limos and separate from the whelmed and the smooth, rich texture is lost.
What happens when you combine acid with milk?
- Adding lemon juice to fresh milk will cause the milk to curdle.
- The flavour of the milk becomes sour to taste
- Some products rely on this reaction to create a unique texture