Food Preservation Flashcards
What are the principals of food preservation
Inhibits microbial activity that causes food spoilage and food poisoning
Inactivates enzymes that cause food spoilage
Prevents microorganisms re entering food by sealing it
Maintains colour taste texture flavour and nutritional value of food
Advantages of food preservation
Avoids waste as they can be preserved before spoil eg apples made into chutney
Preserved out of season food eg frozen strawberries
Add variety as it allows new foods to be produced eg pickles
Saves money as food last longer consumers can stock up
Name 4 methods of home preservation
Freezing
Heat treatements eg jam making
Chemical preservation eg pickling
Dehydration eg drying herbs
What are the underlying principals of freezing
Using low temperatures below 0 degrees to inactivate microorganism growth snd slow down enzyme activity
Converts water into ice making it unavailable to microorganisms
Before freezing foods should be wrapped well
What are the two methods of home freezinf
Quick freezing and slow freezing
What is the method of quick freezing
Food quickly frozen at -25degrees in the fast freeze section
Small ice crystals are formed causing little damage to cell walls
Texture colour and flavour are retained on thawing
What is the method of slow freezing
Food is frozen between 0-18 degrees in the ice box in a fridge or freezer
Large crystals are formed causing damage
Low of nutritional value, texture, colour and flavour on thawing
What are foods that are not suitable for home freezing
Mayonnaise - emulsion separates
Whole eggs - crack due to white expanding
Foods with high water content eg cucumber
Soft cheese - dry and crumbly on thaw
What are the advantages if freezing
Retains sensory characteristics and nutritional value
Saves time as you can bulk buy and freeze
Saves money as individuals can bulk freeze meals for busy days instead of takeaway
Avoids food waste
Makes out of season food available
What are disadvantages of freezing
Initial cost of the freezer can be costly
Bulk freezing can be time consuming
Packaging is needed which can be costly
Defrosting can be time consuming
Guidelines for home freezing
Turn on fast freeze button 3-4 hrs before to reduce temperature from -18 to -25
Cool food beofre freezing
Avoid freezing more then one tenth of the freezer within 24 hrs as it puts pressure on the motar
Freeze foods in usable quantities
Blanch veg before
How to blanch veg
Bring one litre to the boil
Wash peel and chop 100g carrots
Place carrots in boiling water for 3-5 mins
Immedietly place in cold water with ice for 5 mins
Place in freezer bags in usable portions and label with food and date of freezing
Fast freeze section of the freezer
What packaging to use for freezing
Good quality that is strong and airtight and moisture proof
Seal packaging well otherwise freezer burn will occur
If freezing liquids leave room for expansion
Label the name of food quantity and date of freezing
What are guidelines for storing
Store similar foods together to avoid unnecessary searching
First in first out
Foods should only be stored for recommended storing time g beef and chicken 12 mths
Keep freezer full to capacity as majority of energy is used to cool between foods
Avoid keeping door open for long periods of time
How to thaw food
Read instructions as some retain their nutritional value and sensory characteristics if cooked from frozen
Thaw food in fridge as room temo is optimum temp for bacterial growth
Never refreeze thawed food unless cooked
What are the underlying principals of jam making
Boiling fruit at 100 degrees to destroy microorganisms and inactivate enzymes
It also softens food by breaking down cell walls
Adding sugar acts as a preservative the sugar solution draws water out of microbial cells
Presence of pectin and acid allows fruit to set
What are the ingredients of jam
Fruit
Sugar
Pectin
Acid
How to add extra pectin
Commerical pectin eg certo
Use sure set sugar
Mix with pectin fruit eg apples
What does acid prevent
Crystallisation
How to make jam
Weigh our ingredients
Wash jars un hot soapy water and dry and place on baking tray to sterilise in the oven at 140 for 20 mins to remove microbes
Fruit prep remove bruises wash peel and remove stalks
Cook fruit in a greased saucepan and simmer gently to release pectin
Warm sugar at 140 degrees for 5 mins
Add sugar and stir till dissolved
Bring to boil and stir occasionally
If jam is set skim scum from thr top using a ladle and spoon into sterilized jars leaving 1.5 cm at the top
Cover with a wax disk and apply a cellophane cover
Label
Store in a cool dry place
How to set test
Wrinkle - spoon jam into a refrigerated plate and push with finger
Flake - dip a spoon into the jam and allow it to cool flr a minute tilt the spoon and allow jam to run off if set the jam will fall in one large flake
Thermometer test - place sugar thermometr into a pot of jam when it reads 105 jam is set
What are the problems that can occur when making jam
Crystallisation- when too much sugar is added, if jam isnt boiled for long enough, sugar not stirred continuously
Unset jam- insufficient pectin or acid, jam not boiled for long enough as not enough pectin released , jam poured before setting point
Fermentation - insufficient sugar, poor quality fruit, jam not boiled for long enough
What are the underlying principals of chutney making
Boil fruit and veg @100 then simmer to destroy microorganisms
Add sugar
Add vinegar - preservative as it lowers PH
Why use plastic funnel and wooden spoon when making chutney
And plastic lids
Metal can react with the acid in vinegar
Why use brown sugar for chutney
Brown sugar gives richer colour
What are the underlying principals of chemical preservation
Concentrated solution causing water being drawn out of microbial cells by osmosis
Acids lower ph inhibiting microbial growth and inactivation enzymes
What are types of home chemical preservation
Jam making
Chutney making
Pickling
What are the underlying principals of dehydration
Removing moisture and inhibiting microbial growth and inactivating enzymes
What foods are suitable for dehydration
Herbs
Fruit
Veg
Name the 4 types of commercial preservation
Blast freezing
Contact freezing
Cryogenic freezing
fluidised bed freezing
Explain blast freezing
Most common
Food subjected to a blast if cold air -30–40 that circulates food as it travels through a tunnel on a conveyor belt
Takes approx 2.5 hrs
Explain plate freezing
Food placed on or between cold metal pkates by direct contact that have been cooled by circulation of a refrigerant eg ammonia at -30–40
Takes 60-90 mins
Explain cryogenic freezing
Most expensive but produces most superior product
Food placed on a conveyor belt and moved into an insulated chamber and cooled spraying liquid notrogen (-196 degrees)
Freezes within minutes
Explain fluidised bed freezing
Food blasted with cold air from underneath a conveyor belt so food separates separately
What are the underlying principals of canning and bottling
High temps destroy microorganisms and inactivate enzymes
Sealing food in airtight containers prevent re entry
What are the stages in canning process
Food is preped eg veg washed, bones removed, meat ir fish cooked and veg blanched
Cans are lacquered to prevent reaction between food and metal
Either syrup or brine added
Air removed
Cans are hermetically sealed in sterile environment
Cans and food are sterilised snd cooled
Cans are labelled
What are the 3 methods of canning
Aseptic
High acid
Low acid
Describe aseptic canning
Cans and food are sterilised separately at high temps
Food to 120 degrees
Food placed into cans and hermetically sealed and cooled and labelled
Short process
Describe high acid food
Hugh acid food eg fruit require short processing time due to low ph
Heated to 100 degrees for less then 30 mins
Describe low acid canning
Heated to 115 for more then 30 mins
What are the commercial dehydration methods
Fluidised bed drying Acceleration freeze drying Sun drying Fermentation Irradiation
Whats fluidised bed drying
Food subjected to blast of hot air
Food continuously moved to prevent sticking together
20-40 mins
Whats acceleration freeze drying
Food initially frozen at low temps Small ice crystals are formed Ice crystals are then evaporated inna vaccuum chamber by sublimation Takes 9-24 hrs Used for coffee fruit veg ect
What is sun drying
Exposed to direct sunlight in hot climates eg california
Water is evaporated
What is fermentation
Breakdown of carbohydrate by microorganisms to produce carbon dioxide, alcohol and energy
What is irradiation
Exposure to low levels of radiation which passes throigh foods destroying microorganisms, pests and prevents sprouting
What is irradiation legislation
Any irradiation products on sale in Ireland as ther are no irradiation facilities
Any imported food must have RADURA SYMBOL
must contain words irradiated or ionising radiation
What are the disadvantages of irradiation
Vitamin can be eliminated or reduced
Can cause chemical composition of high fat foods to change
May mislead customers into thinking foods are fresh
Can cause large numbers of free radicals to occur
