food preservation Flashcards
what are the principles of food preservation
-inhibits the microbial activity that causes spoilage and food poisoning
-inactivates the enzyme activity that causes food spoilage
-prevents microorganisms re-entering food, by sealing it
-maintains colour, taste, texture, flavour and nutritional value of food as much as possible
what are the advantages of food preservation
-preservation avoids food waste as foods can be preserved before they spoil
-preservation makes out-of-season foods available all year around
-preservation adds variety to the diet, as it enables new foods to be produced
-preservation saves money as preserved foods have a longer shelf life, so consumers can stock up when foods are on special offer
what are the methods of home preservation
-freezing
-heat treatments
-chemical preservation
-dehydration
what is the underlying principle of freezing
-using low temperatures to inactivate microorganisms growth and slow down enzyme activity
-converting water in food into ice, making it unavailable to microorganisms
what are the methods of home freezing
quick freezing and slow freezing
what is quick freezing
food is quickly frozen at -25C in the fast-freeze section of the freezer
what are the effects of quick freezing
-forms small ice crystals in food, causing little damage to the cell walls as the crystals don’t tear or puncture them
-nutritional value, texture, colour and flavour are retained on thawing
what is slow freezing
food is frozen at 0 to -18C in the ice box in a fridge or storage section of a freezer
what are the effects of slow freezing
-forms large ice crystals in food, causing large damage to the cell walls as the crystals puncture or tear them
-loss of nutritional value, texture, colour and flavour occur on thawing
what foods are suitable for freezing
-most fruit and vegetables
-meat, fish and poultry
-soups and sauces
-bread, cakes and pastries
what foods are unsuitable for freezing
-mayonnaise
-cucumbers
soft cheeses
what are the advantages of freezing
-retains the nutritional value and sensory characteristics of food
-saves time, as individuals can bulk-purchase perishable foods avoiding numerous supermarket visits
-saves money, as individuals can bulk-freeze meals for busy days avoiding the need for takeaways
-makes out-of-season foods available all year
-avoids food waste as foods can be frozen before they spoil, extending shelf life
what are the disadvantages of freezing
-the initial cost of a freezer can be expensive
-bulk-freezing meals can be time-consuming as large quantities of food must be prepared and cooked
-packaging is needed for freezing, which can be costly
-defrosting the freezer can be time-consuming and laborious
what are the guidelines for home freezing
-preparation
-packaging
-freezing
-storing
-thawing
explain preparation as a guideline for home freezing
-cool food before freezing to avoid the internal temperature of the freezer increasing causing other food to defrost
-freeze foods in usable quantities to avoid having to defrost more food than is needed
-blanch vegetables before freezing to avoid enzymic spoilage over time
-turn of fast-freeze button 3-4 hours in advance to reduce the temperature from -18C to -25C. this results in quick freezing that retains nutritional value and sensory characteristics of food
explain packaging as a guideline for home freezing
-use good quality packaging that is strong, airtight and moisture-proof
-remove as much air as possible to save space in the freezer
-seal packaging well, otherwise freezer burn may occur, resulting in discolouration, toughening and drying out of protein foods
-if freezing liquids, make sure to leave room for expansion in packaging to prevent tearing
explain freezing as a guideline for home freezing
-place food in the fast-freeze component to allow for quick freezing to retain the nutritional value and sensory characteristics of food. after 24hrs place in the storage section of the freezer
-open freeze foods that will stick together. place in a container after freezing
explain storing as a guideline for home freezing
-keep the freezer full to capacity
-avoid keeping the freezer door open for long periods as warm air will increase the internal temperature causing food to thaw
-use foods in rotation by following the FIFO system
-store similar foods together to avoid unnecessary searching and make it easier to determine when additional foods need to be purchase
explain thawing as a guideline for home freezing
-read cooking instructions on packaged foods before thawing, as many do not require prior to cooking
-place meat or fish to be thawed on a plate at the bottom of the fridge to avoid drips onto other foods, leading to cross-contamination
-thaw food in the fridge, as thawing at room temperature can provide optimum temperatures for bacterial growth
what is blast freezing
-this is the most common method of commercial freezing
-food is subjected to a blast of cold air -30C to -40C that circulates around food as it travels through a specially designed tunnel on a conveyor belt
-approximately takes two and half hours to freeze food
-uses: freezing fruit, vegetables and meat
what is cryogenic freezing
- this is the most expensive method of freezing but it produces the most superior product due to its low temperature which results in tiny ice crystals
-food is placed on a conveyor belt and ,oved into the insulated chamber where it is cooled by spraying with liquid nitrogen
-it freezes food within minutes
-uses: freezing small fruits, e.g. strawberries and shellfish
what is the underlying principle of irradiation
irradiation preserves food by exposure to low levels of radiation which passes through food and:
-destroys microorganisms
-kills pests, e.g. whiteflies
-prevents sprouting on vegetables and slows ripening on fruit
what are the advantages of irradiation
-extends shelf life as it destroys microorganism
-kills insects pests
-slows the ripening of fruit and prevents the sprouting of vegetables
-retains sensory characteristics of food including texture, colour and flavour
