Food preservation and fermentation Flashcards
Vacuum drying
- Foods put into a low pressure chamber
- Water evaporates more easily → ~1-3%
water
Freeze drying
- Uses sublimation
- Food frozen to ~-50 to -80°C so water
turns to ice - Placed in a vacuum to decrease pressure
and heat applied so ice→vapour
- Smoking is a process where foods are put into smokers
and exposed to burning wood in a humidity and
temperature regulated environment - Liquid smoke is also often used
- Cold smoking – dries food but does not cook it, ~__-__°C
- Hot smoking – dehydrates food and partially cooks, __-__°C
- Often used alongside salting and drying
25-35°C
74-85°C
ADDING HEAT
When food is heated to above __°C most bacteria and food spoilage organisms are killed
Can be achieved by a range of cooking methods
Temperature danger zone is between _ and __°C
Need to balance safety and sensory qualities
74°C
5 and 60°C
Pasteurisation: a food
preservation process that heats
liquids to __°C for __sec, or ___°C
for __min, or ___-___°C for -
seconds (UHT) in to kill bacteria,
yeasts, & moulds.
72°C, 15
62°C, 30
138-150°C, 2-6secs
Refrigeration:
The standards require food to be cooled from __°C to __°C in a maximum of __ hours
and from __°C to 5_°C within a further maximum period of _ hours.
60°C to 21°C
2
21°C to 5°C
4
Acid
Water activity first decreased by ______/_______
Food then submerged in vinegar - ≥ _% acetic acid
Firm vegetables and fruits are prepared, hot pickling liquid of vinegar, water, some sugar and flavours is poured over and allowed to cool.
Some foods are first ________ by simmering
salting/brining
5
softened
Fermentation
Fruits and vegetables are _____ and put in a closed container
They leach water due to _____ creating a brine – harmful microorganisms inhibited, beneficial bacteria thrive
Bacterial fermentation of sugar in the vegetables produces ____ ___ which _____ the pH
Examples include white cabbage, cucumbers and green beans
salted
osmosis
lactic acid
lowers
Alcohol
* Alcohol acts as a _______ by killing microorganisms
* Bacteria and fungi cell walls become permeable → ______ of their protein → death
* Usually involves mixing fruit, sugar and hard spirits and leaving for some time
* E.g. rumtopf
* ____ is NOT applied so alcohol remains!
preservative
denaturation
Heat
ADDING FOOD PRESERVATIVES
_________ – inhibit growth of microorganisms e.g. sulfur dioxide, nitrite, nitrate, benzoic acid, sorbic acid
__________ – reduce food oxidation e.g. vitamin C, vitamin E, vitamin A, butylated hydroxyanisole
Antimicrobial
Antioxidant
MODIFIED ATMOSPHERE PACKAGING
_____ removed and replaced with ________ _____/other gases
_________ _____: foods that have been
packaged airtight by a commercial sealing
process.
Oxygen
carbon dioxide
Hermetically sealed
The purpose of edible coatings is:
- To increase shelf life by acting as a barrier to moisture, O2,
CO2, volatile aromas & other compounds whose loss would
lead to deterioration. - To impart improved handling characteristics, such as the
ability to bend more easily without breaking. - To improve appearance through gloss & colour.
- To serve as a vehicle for added ingredients such as flavours,
antioxidants, antimicrobials, etc.
Irradiation:
a food preservation process in which foods are
treated with low doses of gamma rays, x-rays, or electrons.
Effects of irradiation on food:
renders the food less susceptible to deterioration & destroys
many of the micro-organisms
reduces spoilage
lengthens shelf life
sterilises or kills insects
can protect the public from many bacterial foodborne diseases
Define fermentation
The conversion of carbohydrates to carbon dioxide and alcohol by
yeast or bacteria
Sourdough bread
* Starch is broken down by ______ to _____ and ______
* _____ and ______ are metabolised by yeasts and bacteria in the bread
* Yeast and bacteria composition depends upon: _______
- Yeasts follow the _______ _______
amylase
maltose
glucose
maltose
glucose
- pH
- Dough hydration & yield
- Number of back-slopping steps
- Fermentation time between starter feedings
- Leavening
- Storage temperature
- Microbial, chemical and enzymatic characteristics of the flour
homofermentative pathway
Beer
malt production:
* Yeast requires the ___ from the grain to be simple in chemical
structure i.e. ____
* Malt is then mixed with ____ & heated to make it further available to the yeast -> this produces ___ (pronounced wert) a high ____ liquid
brewing:
* involves ______ the wort
* ___ are added and the mixture boiled
* This process -> _______ & _______ the wort; inactivates
enzymes; precipitates protein that contribute to haze & caramelises the sugars
Fermentation:
* Yeast is added which converts the sugars into _____ & ____
gas and fermentation proceeds several days at __°C
* The liquid is chilled to _°C to stop fermentation
CHO
malt
water
wort
sugar
heating
Hops
concentrates & sanitises
alcohol
CO2
10°C
4°C
WINE
______ is produced by fermenting the carbohydrate in grape juice by yeasts
Red wine is fermented at __-__°C
White wine is fermented at __-__°C
Primary fermentation – _ to __ days.
Secondary fermentation – ____ depending on type.
Factors that influence ethanol production are -
Ethanol
22-28°C
12-15°C
3-14
weeks
temperature, sugar concentration, acidity and strain and activity of the yeast
YOGHURT
_____ is broken down to _____ and _____
_______ and ______ are metabolised to ___ ____ following addition of a starter bacteria
Yoghurt is ______ before the addition of _______ _______.
Heating reduces the amounts of other competitive bacteria and also _____ the ____ and _____ proteins.
The mixture is cooled to __-__°C before starter culture is added
Microorganisms interact symbiotically during fermentation in ways
that stimulate each other’s _____
The production of ____ ____ as fermentation progresses reduces
the __. This neutralises the negative charges on the _____ micelles
This means they move closer together forming a __
When the desired ___ and texture are reached fermentation is
stopped by either _____ or ______ the yoghurt.
Lactose
galactose and glucose
galactose and glucose
lactic acid
heated
starter culture
denatures
whey and casein
40-45°C
growth
lactic acid
pH
casein
gel
pH
cooling or heating
