section c Flashcards
why do we cook food?
- adds variety to diet
- aroma in food released
- destroy harmful bacteria
- make food less bulky
- make it easier to eat and digest
- improved flavour
- have hot food in cold weather
- more attractive and colourful
- textures changed
- to destroy natural poisons in foods
how does cooking food make food less bulky?
volume of some food is reduced when cooked e.g., spinach or apples
how does cooking food make it easier to digest?
we change the structure of the food e.g., connective tissue in meat softens
how does cooking food destroy natural poisons?
some contain natural poisons that need to be destroyed to make the food safe to eat e.g., red kidney beans
what is the definition of palatable?
pleasant to taste
what are the three ways of transferring heat?
- conduction
- convection
- radiation
what is the definition of conduction?
where heat is transferred from one molecule to another
list examples of conduction
- boiling
- simmering
- blanching
- poaching
- baking
- frying
- microwaving
- roasting
- braising
- casserole
what is the definition of convection?
where warm molecules rise and the cooler molecules fall closer to the source of heat
list examples of convection
- boiling
- simmering
- blanching
- poaching
- baking
- frying
- roasting
- steaming
- braising
- casserole
what is the definition of radiation?
where heat is passed by EM waves from one place to another
list examples of radiation
- barbecuing
- grilling
- microwaving
- chargrill
what are the water-based methods of cooking?
- steaming
- boiling and simmering
- blanching
- poaching
what are the dry heat and fat based methods of cooking?
- dry-frying
- shallow frying
- deep frying
- stir-frying
how is the nutritional content affected by methods of cooking?
- enrichment/loss
- increasing/reducing calorific value
- vitamin losses
e.g., if we cook foods in fat, fat and calorie content increase
e.g., if we cook foods in liquid, water-soluble vitamins will leach into liquid
how is protein affected by methods of cooking?
not affected
how are carbs affected by methods of cooking?
- fibre is softened; especially w moist methods
- starch reduced when food cooked in water bc starch dissolves
how is fat affected by methods of cooking?
- may be reduced when food cooked e.g., grilling allows fat to drain out of food
- cooking food in fat increases fat and calorie content
how is vitamin A affected by methods of cooking?
not affected except for frying where high temperatures used
how is vitamin D affected by methods of cooking?
not affected and does not dissolve in water
how is vitamin E affected by methods of cooking?
not affected
how is vitamin K affected by methods of cooking?
not affected
how is thiamine (vitamin B1) affected by methods of cooking?
- soluble in water so the cooking liquid should be used e.g., in a sauce or gravy
- easily destroyed by heat
how is riboflavin (vitamin B2) affected by methods of cooking?
- soluble in water
- destroyed by heat in presence of alkali e.g., bicarb of soda
how is niacin (vitamin B3) affected by methods of cooking?
- soluble in water so the cooking liquid should be used e.g., in a sauce or gravy
- more resistant to heat than any other B vitamin
how is folate/folic acid (vitamin B9) affected by methods of cooking?
- less sensitive to heat than other vitamins
- destroyed if food is reheated or kept warm for long
how is cobalamin (vitamin B12) affected by methods of cooking?
soluble in water
how is ascorbic acid (vitamin C) affected by methods of cooking?
- destroyed by moist and dry heat
- dissolves in water so cooking methods should use little to no water
how are minerals affected by methods of cooking?
not affected
how do cooking methods change sensory properties?
- steaming make food light in texture; more palatable
- frying makes food attractive in colour (golden brown)
- bright colour of veg is retained in microwave
what is the definition of a colloidal structure?
when at least two ingredients are mixed together
what are the working characteristics in carbohydrates?
- gelatinisation
- dextrinisation
- caramelisation
what is the definition of gelatinisation?
- flour mixed with a liquid and heated
- causes mixture to thicken
how does gelatinisation occur?
- starch grains cannot dissolve in the liquid
- starch grains form a suspension
- liquid is heated causing starch grains to swell at 60c
- more heat is applied causing the starch grains to break open
- this causes mixture to thicken at 80c
mixture must be stirred as its being heated to prevent lumps forming
how does dextrinisation occur?
the starch in the flour is changed into a sugar
what is the definition of dextrinisation?
- applying dry heat to products with flour
- causes crust of product to become brown
what is the definition of caramelisaton?
the browning of sugar when heated
how does caramelisation occur?
- moist heat applied to sugar
- sugar melts and becomes syrup
- at 154c sugar starts to change colour
- longer the sugar is heated, the deeper the colour of the caramel and the harder it will set when cooled
what are the working characteristics in fats/oils?
- shortening
- aeration
- plasticity
- emulsification
how does shortening occur?
- fat coats flour grains to provide waterproof coating
- prevents development of gluten
- gluten cannot absorb water
- results in crumbly texture
what is the definition of aeration?
the process of trapping air in a mixture to cause it to rise
how does aeration occur?
- fat and sugar creamed together traps air
- mixture heated causing air to expand
- makes cakes rise and gives light texture
e.g., all-in-one cake mixtures, creaming
what is the definition of plasticity?
the ability of a solid fat to soften over a range of temperatures
what is the definition of plasticity?
fats melting at different temperatures. some products designed to have a lower melting point to give a desired quality
e.g., a spread that can spread straight from the fridge
what is the definition of emulsification?
the process of using an emulsifier to prevent a mixture of oil and liquid from separating
how does emulsification occur?
- oil and liquid mixed together e.g., salad dressing
- they will separate when left to stand
- emulsifer added to prevent separation
e.g., egg yolk (containing lecithin)
what are the working characteristics of proteins?
- coagulation
- foam formation
- gluten formation
- acid denature
what is the definition of coagulation?
when moist or dry heat is applied to protein foods, they set. if they are overheated, they become tough and more difficult to digest
what happens to meat when cooked?
- muscle fibres begin to coagulate between 40-60c
- after 60c fibres shrink and juice squeezed out
- changes from red to brown colour
- lean cuts of meat quicker cooked than tougher cuts
what happens to fish when cooked?
- muscles shrink due to small amount of connective tissue
- fibres become tough if cooked too long
what happens to eggs when cooked?
- egg white coagulates at 60c
- egg white changes from opaque to white
- egg yolk coagulates 70c
- if egg heated too quickly, syneresis occurs
what is the definition of syneresis?
usually refers to eggs; if overcooked, proteins shrink as they coagulate and separate from watery liquid
what happens to milk when cooked?
skin forms on top - this is protein coagulating
what happens to cheese when cooked?
protein coagulates
what happens to flour when cooked?
gluten coagulates
what are the uses of coagulation? give examples
- binding ingredients together e.g., fish cakes
- coating products to protect when frying e.g., scotch eggs
- to set a mixture e.g., egg custard
what is the definition of foam formation?
a foam being produced when eggs are whisked
how does foam formation occur in proteins?
- egg whites whisked to produce a mixture of gas (air) and liquid (egg white)
- albumin stretched and traps air
- if left to stand, egg whites eventually collapse and become liquid again
- once collapsed, cannot be whisked again
what is the definition of gluten formation?
strong flour with high gluten content used to provide structure
what are the two proteins found in wheat which form gluten?
- glutenin
- gliadin
how does gluten formation occur?
- gliadin and glutenin form gluten
- gluten developed in bread dough when kneaded
- this creates bread structure
what is the definition of acid denaturation?
acids used to change shape and structure of protein foods e.g., to tenderise meat
how does acid denaturation occur?
- acid causes change in protein structure
- long chains of amino acids unfold
- softens meat tissues
how is vinegar used in acid denaturation?
- tenderises meat as acid softens meat tissues
- provides soft texture
how is lemon juice used in acid denaturation/oxidisation?
- prevents enzymic browning to improve appearance of food
- sets mixtures that contain protein e.g., cheesecakes
what are lemon juice and vinegar examples of?
acetic acids
what is the definition of enzymic browning?
a reaction between a food product and oxygen resulting in a brown colour e.g., potatoes or apples
what is the definition of oxidisation?
occurs when fruit and veg are cut and exposed to the air e.g., apples, bananas
what are the working characteristics of fruit and veg?
enzymic browning/oxidisation
what are the working characteristics of raising agents?
- yeast
- chemical agents
- air
- steam
what is the definition of yeast?
a raising agent used in bread making to give bread lightness and cause it to rise
how does yeast work?
- given food, warmth, moisture and time
- breaks down food into carbon dioxide by fermentation
- gives bread mixture lightness
- causes bread to rise
what is the definition of fermentation?
giving yeast warm, food, moisture and time to produce carbon dioxide and alcohol
what is the definition of chemical raising agents?
chemicals that can be used to make baked products rise
how do chemical raising agents work?
- when heated, co2 produced
- gives food product lightness
what are the properties of food with too little raising agent?
- lack of volume
- close texture
- insufficient rising
- shrinkage
what are the properties of food with too much raising agent?
- poor colour and flavour
- coarse texture
- over-rising then collapsing e.g., sunken cake
list examples of chemical raising agents - give properties
- bicarb of soda: dark colour produced
- baking powder: alkali+acid
what is the function of air in baked goods?
used in whisked sponges and meringues to give lightness
how does air cause baked goods to rise?
- air incorporated into mixture
- air expands quickly
- produced lightness
how can air be added to a mixture?
- sieving flour
- rubbing fat into flour e.g., shortcrust pastry
- creaming fat and sugar e.g., cake mix
- beating mixtures e.g., batter
- folding and rolling e.g., flaky pastry
- adding whisked egg whites e.g., meringues
what is the function of steam in baked goods?
causes products that contain a lot of liquid e.g., eclairs/choux pastries, to rise
how does steam cause baked goods to rise?
- steam produced when products bake from liquid present in mixture
- hot ovens produce sufficient steam
- causes product to rise
what are the liquids that produce steam when baked?
- milk
- water
- eggs
how does sight affect food choices?
- appearance (aesthetics) make it look less/more appetising
- colour, size, shape, garnish and decoration evoke different feelings
- cooking methods affect appearance e.g, golden brown colour from frying
- age affects appearance e.g., red meat becomes darker, fruit ripens and changes colour
- size affects appearance e.g., cakes rise
how does sound affect food choices?
- some food products make sounds
- sizzle of bacon when cooking, crunch of crisps
how does smell affect food choices?
- volatile aromas released from foods
- this can stimulate digestive juices and make food seem more appetising
- some aromas pleasant e.g., spiciness in curry
- others unpleasant e.g., toast burning
how does taste affect food choices?
- bitter, sweet, sour, salt, umami
- flavour develops when food is chewed and mixed with saliva
- ingredients allow detection of flavour
how does touch affect food choices?
- surface of tongue sensitive to different sensations
- moist, dry, soft, sticky, gritty, crumbly, mushy
- mouth feel; if missing, food is considered to be unpalatable
- method of cooking + working characteristics determine different feelings e.g., potatoes soft if boiled but crunchy exterior if roasted
what is the definition of umami?
savoury taste
what is the definition of aesthetic qualities?
properties that make a product attractive to look at or experience
what is the definition of organoleptic?
the sensory qualities of a food product
what is the definition of sensory analysis?
tests that identify the sensory characteristics of products (taste, texture, appearance, mouth feel, colour)
how can you set up a tasting panel?
- dont allow testers to communicate with eachother
- give tasters piece of apple to clear palate
- use small quantities of food and identically sized plates
- use same garnish or decoration
- don’t give too many samples at once
- serve at correct temp
- use clean spoons or forks each time
- use codes for products to prevent testers being influenced by name of product
- have charts ready before testing
- make sure testers know how to fill in charts
why are tasting panels used?
to evaluate product acceptability by finding out the opinions of the consumer
what are rating tests?
giving testers one or more samples of food from ‘extreme like’ to ‘extteme dislike’. there are no details about specific elements of a food product
what is difference/comparison testing used for?
seeing whether people can tell the difference when
- an ingredient or quantity of ingredient is changed
- manufacturers are copying another brand
e.g. triangle testing
what is triangle testing?
- three samples given to tester
- two are the same
- tester asked to identify odd one out
how is a ranking test used?
to sort a variety of foods into order. they are ranked in order of either
- a specific attribute e.g., sweetness
- preference on an enjoyment scale
what is a profiling test used for?
finding out what people particularly like about a food product to build a profile according to a range of sensory qualities e.g., saltiness
how is a profiling test carried out?
- testers give a score out of five for each sensory quality
- scores are totalled and divided by number of testers for each quality
- this gives average scores
what conditions are needed for bacterial growth?
- time
- temperature
- moisture
- food availability
what are properties of bacteria?
- active in warmth, moisture, food and oxygen (optimum conditions)
- able to reproduce rapidly via binary fission
- able to grow rapidly in neutral pH conditions
- most active in temp range of 5-63c (danger zone)
- optimum temp of growth is 37c
- become dormant below 0c
- most cannot survive above 70c
- can grow aerobically and anaerobically
what micro-organisms cause changes in food?
- yeasts
- moulds
- bacteria
what is the definition of deteriorate?
when a food starts to decay and lose freshness
what is the definition of enzymes?
proteins that speed up chemical reactions
what is the definition of micro-organisms?
tiny living things such as bacteria, yeasts and moulds that cause food spoilage; can only be seen through a microscope
what is the definition of bacteria?
single celled organisms present in the air, soil, on animals and on humans
what is the definition of high-risk foods?
foods which are the ideal medium for the growth of bacteria or micro-organisms
list examples of high-risk foods
- chicken
- raw fish
- eggs
- cooked meat
- dairy
- cooked rice
list examples of low-risk foods
- bread
- fresh fruit and veg
- honey
- jam and preserves
- candies
- pickles
what is the definition of pathogenic bacteria?
harmful bacteria which can cause food poisoning
what is the definition of pH?
a measure of alkalinity or acidity
what is the definition of danger zone?
the temperature range (5 to 63) in which bacteria grow rapidly
what are the properties of moulds?
- visible to eye; thread-like filaments on surface of food (black, blue or white)
- reproduced by producing spores which travel in air; spores settle, germinate and multiply into new growths
- harmful when produce mycotoxins (poisonous)
- not all harmful; some used in food manufacture to produce specific flavours e.g., danish blue/stilton cheese
what are the conditions needed for mould growth?
- require oxygen to grow
- grow quickly in moist conditions at temps of 20 to 30
- grow slowly in dry, cold conditions
- grow on food that may be dry, moist, acid, alkaline, or has salt or sugar concs
what is the definition of food spoilage?
damage to food caused by the natural decay of food or by contamination by micro-organisms
what are the conditions needed for yeast production?
- active in warm, moist conditions with food for growth and reproduction
- can grow anaerobically
what foods do yeast cause food spoilage in?
high-sugar foods such as fruit, jam and fruit yoghurts
what are the signs of food spoilage?
- enzyme action; speed up enzymic browning
- natural decay; sped up by enzymes
- yeast production
what is the definition of food-spoilage bacteria?
bacteria that cause food to go bad but do not usually cause food poisoning
how can enzymic browning be reduced?
- high temps e.g., blanching cut veg in boiling water
- acidic conditions e.g., dipping cut fruit into lemon juice
how can micro-organisms be helpful in food production?
- some bacteria used in making cheese and yoghurt
- bread and brewing - enzymes in yeast active in fermentation process
- cheese - enzymes speed up ripening stage
what should you check for when buying food?
- labelling and date marks; provide information about use by date, storage and cooking information
- visual checks; check food looks fresh, is within best before date, packaging isn’t damaged
- reputable supplier; is the shop clean? is the food stored correctly?
what is the definition of shelf life?
how long a food product can be kept safely and remain of high quality
what is the definition of low-risk foods?
foods which have a long shelf life, such as dried foods
what information is required by law on food labels?
- product name
- list of ingredients
- storage conditions
- date marking
- preparation and storage instructions
- place of origin
- weight
- allergies
- nutritional labels
- GM ingredients
what temperature should a domestic fridge be kept at?
0 to 5c
what are the advantages of refrigerators?
- provide safe storage of food
- less risk of food poisoning
- growth of food-poisoning bacteria is slowed
how can you sensibly use a fridge?
- avoid opening door regularly as warm air enters each time
- avoid putting hot food which raises temperature and fills inside with steam, raising temp of other foods
- cover food
- maintain consistent temperature; inc in temp can lead to increased bacterial growth
- keep raw and high-risk foods away from other foods; store on bottom shelf of refrigerator
what temperature should a domestic freezer be kept at?
-18c
what can a freezer be used to store?
- already frozen foods
- cant be used to store fresh foods
- cant be used to store foods with high water content
- veg can be kept frozen
- high water content fruits don’t freeze successfully e.g., strawberries
what happens when a food is thawed?
- structure damaged
- loss of colour, flavour, texture and nutritional value
you should never refreeze food after it has thawed - bacteria grow quickly in thawed food because the cells have been damaged
what is freezer burn?
when greyish-white marks appear on food when it has been packaged badly. the food dehydrates and, although safe to eat, will change colour, texture and flavour
what is the definition of cross-contamination?
micro-organisms transferring from raw to cooked foods and causing infection when preparing food
how can cross-contamination be prevented?
- avoid raw and cooked foods touching each other
- don’t let blood/juices from raw food drip onto cooked foods e.g., putting raw meat above cooked foods in refrigerator (direct contamination)
- don’t let bacteria transfer during handling or preparation e.g., from hands (indirect contamination)
what rules should be followed for food hygiene?
- wash hands thoroughly before handling food and between handling different types of food
- keep raw and cooked foods separate; use different equipment to handle them
- cover cuts and don’t cough or sneeze over food
- keep all working surfaces and utensils clean using antibac spray
- cover and cool cooked foods rapidly and refrigerate as quick as possible
- dont put hot foods in refrigerator as it raises temp of other foods
- keep pets away from food preparation areas
- keep bins covered
what are the main causes of food poisoning?
- leaving food at room temp for longer than safe period of max four hours
- keeping hot foods below 63c
- not reheating foods to correct temp (over 72c) for a long enough time
- not thawing foods properly
- preparing food too far in advance
- undercooking high-risk foods
- not allowing foods to cool before putting them in freezers
- increased microwave use; food not defrosted or reheated to correct temp
- increased use of cooked-chill foods; high-risk
what are the bacteria that cause salmonella and what are their possible sources?
- salmonella: poultry, eggs, meat
- staphylococcus aureus: food handlers
- clostridium perfringens: raw foods e.g., meat and veg
- bacillus cereus: cereals, e.g. rice
- campylobacter: unpasteurised milk, birds
- listeria: soft cheese
- e.coli: cattle, raw meat, raw milk
what are the critical temperatures?
- 72c; cook foods at this temp for at least 2 mins to kill most bacteria (spores not killed)
- 5-63c; danger zone, bacteria multiply rapidly
- 0-5c; bacteria multiply slowly
- 0c; bacteria dormant
- 18c; bacteria will survive but not multiply
