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
What is curdling?
Curdling is when the milk protein, casein, joins together or coagulates to form tiny lumps or clots
What nutrients are found in eggs?
- protein
- B vitamins (B12)
- vitamin A and D
- iron
- phosphorous
How is a high level of Omega-3 egg formed?
Polyunsaturated fatty acid Omega-3 would be added to the hens’ feed.
What does sugar contribute to denaturing eggs?
It increases coagulation temperature.
What does acid contribute to denaturing eggs?
It lowers coagulation temperature
At what temperature do egg whites and egg yolks coagulate?
62-65 degrees (egg whites)
65-70 degrees (egg yolks)
What are the factors contributing to the coagulation of eggs?
- concentration
- acid
- sugar
What does adding Salt do when beating egg whites?
- adding salt will help create a more stable, stiff foam without influencing the flavour as if helps bring the proteins together.
- the salt and beating contribute to the denaturation of the egg protein
What does adding acid to water when poaching eggs do?
Adding acid can assist in the denaturation process. Combining heat and an acid helps to denature the egg protein so it coagulates and holds it’s shape at a lower temperature, making the end product more appealing.
Describe the physical and sensory properties of meat
Lean meat is composed of bundles or long muscle fibres. Each fibre has a wall of elastin and is filled with water carrying dissolved protein, mineral and extractives. These fibres create the grain of the meat. The bundles of fibres are held together with collagen, which dissolves into gelatine during wet cooking.
What makes meat tender?
The tenderness of a cut of meat depends on the age of the animal and the part of the body from which it comes.
Describe the properties of the animals legs and neck
The animals legs and neck are hard-working muscles and highly developed, so their is a greater build-up of hard connective tissue-the resulting cute if meat are tougher, darker in colour and have a stronger flavour
Describe the properties of meat around the ribs, back and rear.
The meat around the ribs, the back and the rear move less when the animal is in the pasture and produces the most tender cuts of meat.
What other factors contribute to the tenderness of the meat?
- methods of preparation
- methods of cooking
- cut selected
- meat can be partially tenderised by scoring or pounding or cutting across the grain
- marinating
What is the nutrient content of meat?
- protein
- iron
- zinc
- vitamin B12
- fats (saturated fats, fat-soluble vitamins)
How much of raw lean meat is made of water?
70%, which reduces after cooking
Why is a dry method of cooking used for some meats?
The cuts of meat have enough water present in the tissue to enable the conversion of the protein, collagen, to gelatin.
Why is a wet method of cooking used for some meats?
This is a slow way of cooking meat that is suitable for less tender cuts of meat. These cuts do not have enough water present in their tissues to convert collagen to gelatin. Therefore, the long, slow, wet cooking softens the connective tissue that makes meat tough.
Changes that occur when meat is cooking: muscle fibre
The proteins in the muscle fibre begin to change shape (denature). As the proteins change, there is contraction in the direction of the muscle fibre, resulting in the piece of meat shrinking and becoming hard.
-the longer the meat is heated, the tougher it becomes.
Changes that occur when meat is cooking: connective tissue
The tough collagen, which makes up connective tissue, must be cookies sufficiently to convert it to water-soluble gelatine so that is becomes tender enough for us to bite through
Changes that occur when meat is cooking: fat
During cooking the fat melts and acts as a lubricant so that the muscle fibre appears less tough. Fat also contributes to the flavour and aroma of cooked meat.
Changes that occur when meat is cooking: water
When the meat is heated, a little water will flow out of the meat as the proteins begin to denature. Most of the water remains locked within the proteins.
Meat cooked for too long will become dry because the water has been lost
Nutrient content of poultry
Poultry has the American amount of protein as red and other white meats, less saturated fat and more polyunsaturated fat.
Describe the thigh and leg meat of poultry
They are the active muscles of the bird so they are the tough cuts. They are a darker in colour because they require more oxygen to move about and are higher in fat
-best for wet method of cooking
Describe the breast of poultry
Domestic checked do not fly, so their breast meat is white and tender because there is less connective tissue.
-best for dry method of cooking
Describe the physical and sensory properties of seafood
The muscles are arranged in layer or short fibres. These bundles of short fibres are surrounded by very thin sheet ps of delicate connective tissue. Fish doesn’t contain much connective tissue (3% only) which makes it fragile and easily converted to gelatine
Describe the sensory properties of oily fish
The oil is dispersed throughout a darker coloured flesh and they have a strong flavour.
e.g. Salmon, tuna, trout, sardines, mackerel and gem fish
Describe the sensory properties of fish in the white classification
These fish have a white flesh and a delicate flavour. The oil is contain in a small sac near the liver.
E.g. Whiting, flathead, flake, garfish and bream
Describe the sensory properties of raw fish
- translucent
- firm to touch
- juices are clear and watery
Describe the sensory properties of fully cooked fish
- flesh is opaque
- flakes just begin to separate
- juices are milky white
Describe the chemical properties of seafood
- fish has a high water content (70% of flesh is water)
- 20% of flesh is protein
- fat in fish is a good source of omega 3 (especially oily fish)
