food spoilage and preservation Flashcards
what cause food spoilage on a product?
microorganisms
how do microorganisms cause food poisoning?
by producing toxins, waste products or poisons that contaminate the foods
what are the typical microorganisms?
bacteria, yeast, moulds
what the signs of food spoilage?
-a sour smell or taste
-areas of mould on food
-slimy feel to the surface of the food
-a loss of moisture leading to wrinkled food that can be discoloured
what are bacteria most likely to cause?
food poisoning
what are the conditions needed for bacteria growth?
-time (every 20 minutes- called binary fission)
-temperature- (24C=optimum temp + 5C->63C is the danger zone)
-Food- (hbv protein and moisture= ‘high risk food’)
-moisture
-pH(bacteria needs neutral conditions to grow)
-oxygen
what is binary fission?
where the bacteria multiplies every 20 minutes
what is the danger zone?
between 5->63C
what is the optimum temp for growth of bacteria?
24C
what is a ‘high risk food’?
a food that promotes the growth of bacteria and eventually causes food poisoning. a hbv protein with moisture
what does acid do to bacteria?
slows down growth
what are some high risk foods?
meat, eggs, fish, cheese, milk
how does food poisoning happen?
if harmful bacteria contaminate food and then have the correct conditions to grow
what are some causes of food spoilage?
insects, pets, cleaning products (bleach), dust
why may pathogenic bacteria cause death in young children, pregnant women and elderly?
as they have lowered immune systems and their stomach acid can’t fight all the bacteria
what are some examples of pathogenic bacteria?
salmonella and stapphylococcus aureus
what are the sources of salmonella?
raw poultry, eggs, raw meat, milk
what are some symptoms of salmonella?
onset diarrhoea, vomiting, fever
how should you prevent cross contamination?
-wash hands before and after handling food
-never wash raw chicken
-store all foods in the correct position in fridge
-cook meat, eggs and fish thoroughly
-wash fruit and veg
-keep animals away from food
- cover cuts, tie back hair
-use correct chopping boards
how stop/prevent bacterial growth?
chill (fridge)
freeze
cook-chill
cook-freeze
canning
bottling/UHT/pasteurisation + sterilisation
what temperature should a fridge be kept at?
between 1-4C
what should be kept on the top shelf of the fridge? and why?
dairy products, deli items
as the fridge temp cools as rises and they are ‘high risk foods’ so should be kept at the coldest part to prevent food spoilage
what should be kept on the middle shelf of the fridge?
cooked foods, leftovers- must be cooled, cakes, jams, pickles
these should all be kept in leak proof container and they need to be kept away from raw foods to prevent cross contamination
what should happen to leftovers before getting put in a fridge and why?
they should be cooled first as if not steam rises and causes moisture to build up and the liquid can drop and cross contaminate other foods
how long do leftovers have to cool before being placed in a fridge?
90 minutes
what should be kept on the bottom shelf of the fridge?
raw meats and fish
these should be kept in leak proof containers and kept at the bottom as they could leak and cause cross contamination
what should be kept in the crisp drawers of the fridge?
fruit and vegetables to prevent oxygen entering and causing spoilage
what can be kept on the door of the fridge? and why?
drinks, butter etc…
as they only need light refrigeration
what should happen to old and new foods in a fridge?
they should be rotated, so newest at the back and oldest at the front to prevent food waste
what does storing food in a fridge do to the bacteria?
it reduces the growth/ slows it down and extends the shelf life by 5 days
what temperature should a freezer be kept at?
-18C
what is the shelf life of food in a freezer?
3 months
what does freezing do the bacteria?
it makes the bacteria dormant
what temp should a commercial freezer be kept at and what is the shelf life of foods when stored in it?
-29C and extends shelf life of up to 1 year
what are some rules when storing foods in a freezer?
- don’t leave the door open
- temp should be -18C
- label all foods
- don’t re-freeze defrosted foods
- all foods should be kept in air tight containers to prevent cross contamination
why should defrosted foods never be refrozen?
as people can lose track of use-by date, during this time of defrosting bacteria has had time to multiply, increased chance of food poisoning and will decrease the sensory qualities
why do freezer’s have star ratings?
is to let the user know how long the food can safely be stored
e.g. **= 1 month at -12C
***= 3 months at -18C
what temperature should food be cooked to before chilling and storing in a fridge? and what does this do?
63C
kills all bacteria
how long can already cooked be stored in a fridge?
3 days
what happens to foods that are canned?
food is sterilised in airtight containers
if food is stored at room temp, how should it be stored?
in an airtight containers, in neutral conditions, use an acids to slow down bacteria growth as it’s at its optimum temp (24C) at room temp
what is a use-by date?
is the date which after there is no guarantee that the food is safe to eat (about safety). food usually shouldn’t be consumed after this date.
what is the best before date?
encouraged date that the food will be at its best quality and won’t have changed (nothing to do with safety)
what is temperature probe?
a sensor that is used to measure the internal temperature of food.
why is a temperature prope placed in the centre of food?
as the core cooks last
what temperature should the core of the food be to prevent food poisoning?
73C and usually used in high risk foods
how should a temperature probe be used?
-turn on and reset
-sterilise probe
-insert into centre
-don’t let probe touch metal tray (as may affect the final temperature)
what are each coloured chopping used for?
red=raw meat
blue=raw fish
green= fruit and veg
white= hot food
what is food preservation?
helps keep food fresh and edible for longer to prevent it from spoilage
what are some alternative methods to food preservation then chilling (fridge) and freezing?
drying, vacuum packing, sugaring, pickling, canning, MAP, chemical preservation, salting, smoking
when drying food, what does it do?
it slows down the actions of enzymes and it removes the moisture in foods so that bacteria can’t grow. this happens with fruit, e.g apricots
also happens at room temp
when freezing, what do it do?
freezing turns the liquid into ice. bacteria cannot grow live liquid. once defrosted the food should be consumed quickly
happens at -18C
when vacuum packing food, what does it?
it removes all the air. e.g. cheese , bacon
when chilling food, what does it do?
slows down the growth of bacteria and extends shelf life by 5 days
happens between 1-4C
when pickling food, what does it?
it uses vinegar, which acidic that micro-organisms cannot grow in it
when canning food, what does it?
this is when food is cooked and then sealed in cans or jars. the heat kills micro-organisms and then sealed so that it will keep the food fresh for a very long.
when MAP food, what does it do?
its a mixture of gases that surrounds food and extends the product e.g crisps or bags of salad.
