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Food Processing Technology > 4. Cleaning, sorting, grading > Flashcards

4. Cleaning, sorting, grading Flashcards

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1
Q

what is cleaning

A

preliminary operation to remove contaminants from raw materials that will be processed

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2
Q

purpose of cleaning

A

remove contaminants, from innocuous to hazardous
a. for the sake of final consumer (safety)
b. protecting processing equipments

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3
Q

what to consider in the cleaning stage

A
  1. higher possible efficiency of contaminant removal
    - ratio of energy input and % of contaminants removal
  2. minimal loss or damage to raw materials being cleaned
    - minimizing bumping, cracking, other measn causing physical damages
  3. precautions avoiding recontamination after cleaning
    - arranging process flow to avoid cross contamination
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4
Q

cleaning methods based on application of water

A
  1. dry cleaning
    (screening, brushing, aspiration, magnetism, electricity)
  2. wet cleaning
    (soaking, spraying, fluming, flotation)
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5
Q

advantages and disadvantages of dry cleaning

A

(+)
- low cost
- convenient
- surface left dry

(-)
- spread of dust
- risk of recontamination
-dust explosion hazard

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6
Q

careful control of dust methods

A
  • dust proofing equipments
  • removal of dust by gas-solid separators (cyclones, rigorous housekeeping, etc)
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7
Q

advantage and disadvantage of wet cleaning

A

(+)
- highly efficient for soiled raw materials (eg fruits, vegs, tubers)

(-)
- large quantity of high purity water required
- large quantity of dirty effluent produced

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8
Q

principles of screening

A
  • used to remove contaminants of CONSIDERABLE DIFFERENT SIZE from food being treated
  • usage of size separators based on perforated beds or wire mesh
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9
Q

two methods of screening

A
  1. scalping
    raw material pass through screen, contaminants retained
  2. de-dusting
    raw materials retained, contaminants pass through screen
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10
Q

examples of devices used for screening

A
  1. flatbed screening unit
    - one or more flat sieve decks fixed in a dust tight casing
    - shaken by different devices
  2. rotary screen
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11
Q

principles of aspiration

A
  • exploits differences in aerodynamic properties (buoyancy) of food and contaminants
  • feeding of raw material to carefully controlled upward air stream; denser material will fall, lighter material will be blown away depending of velocity
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12
Q

principles of magnetism

A
  • removal of ferrous metal using permanent/electromagnets
  • particulate foods passed over magnetized drums or conveyor belts; powerful magnets located above conveyors
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13
Q

application of aspiration

A

cleaning cereals, peas, beans

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14
Q

source of metal contaminants

A
  • growing field
  • picked up during preliminary operations
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15
Q

principles of electricty cleaning

A
  • used when surface charge on raw materials differ from contaminating particles
  • distinguish grains from other seeds of similar geometry but different surface charge
  • feed is conveyed on charged conveyor belt, charged particles attracted to oppositely charged elecrode accoridng to surface charge
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16
Q

why should wash time be kept to minimum

A

washing after pee;ing/cutting/pitting may results in loss of soluble components (sugars, vitamins, minerals0

17
Q

benefits of cold water in wet washing

A
  • reduce respiration and retard softening
  • wash water is cooled and chlorinated (10-100ppm) to reduce number of surface microflora
  • fluming in cold water minimizes exposure to air and help retard bruising of fruit enzymatic browning
18
Q

factors affecting efficiency of wet cleaning

A
  1. amt of washing water
  2. temperature
  3. force applied
  4. acidity (may retard enzymatic activity)
  5. mineral content (Ca) may dislodge bacteria from surface
19
Q

how to improve soaking efficiency

A
  1. move water relative to product or move product relative to water
  2. sparging compressed air
20
Q

common wet cleaning/washing methods

A
  1. belt conveyor by sprays of water
  2. roller conveyor by sprays of water (for berries and other soft fruits)
  3. rotary washers (with thin rods or wire mesh at which debris can fall through)
  4. flotation washers (with water recirculation, commonly used for peas)
  5. brush washers (with cylindrical rotating brushes, used for root crops)
21
Q

how does combo washing machine work

A

dry soil removal, water saving, gentle washing and stone rmoval

(version without dry soil/stone removal possible)

22
Q

advantage of combo washing machine

A
  • low water consumption
  • good washing results, even for soil and clay
  • low operating costs
  • dry preliminary soil removal
  • continuous, reliable stone removal
23
Q

difference between sorting and grading

A

sorting: takes into acc one quality attribute only
grading: takes into acc combination of quality attributes

24
Q

principles of sorting machines

A

exploit differences in properties to separate materials based on
1. weight (eggs, fruits, vegs)
2. size (screening, length and diameter separator)
3. shape (disc/cylinder sorter)
4. photometric characteristics (color sorter)
5. aero and hydrodynamic (aspirator/buoyancy separator)

25
Q

equipments for sorting and grading

A
  1. disc separator (based on shape and size)
  2. flat bed screen/vibrating screen (with circular or square cross sectioned holes)
  3. rotating drum screens (concentric drum)
  4. series consecutive roller drums
  5. parallel consecutive drum screen
  6. roller sorter (gap between rollers widen as conveyor moves - small sized particles falll through first)
  7. groves and grader (belt and roller sorter)
  8. twin screw
  9. mechanical color sorting
26
Q

formula for sortation effectiveness

A

[P Xp R (1-Xr)] / F Xf F (1-Xf)

P = product outflow
F = feed outflow
R = reject outflow
Xp mass fraction of desired materials in prod
Xf mass fraction of desired materials in feed
Xr mass fraction of desired materials in rejects

27
Q

Types of peelers

A
  1. abrasive oeeler
  2. roller peeler
  3. lye peeling
  4. dry caustic peeling
  5. steam peeling
28
Q

disadvantage of abrasive peelers

A

generates uneven appearance and considerable waste (25%)

29
Q

mechanism of abrasive peelers

A

cylinder coated with coarse carborundum powder

30
Q

advantage of roller peelers

A
  • good results without flat peeling
  • carborundum coated with varied granularity for low peeling losses
  • rollers with knives for optimal surface quality
  • low water consumption
  • half quick system, easy changeover of peeling rollers
  • all parameters can be set individually
  • easy to operate
  • easy cleaning
  • secondary peeling option for second quality level
31
Q

principles of lye peeling

A

dip product in hot caustic soda (1-2% NaOH, 100-129C), then remove peel with high pressure water

loosening of peel due to beta elimination of cell wall components

32
Q

principles of dry caustic peeling

A

vegetables dipped in 10% NaOH, softened skin removed with rubber disks or rollers

  • reduced water consumption
  • reduced product loss
33
Q

principles of steam peeling

A

produce subjected to steam at high pressure (1500kPa) then discharged suddenly to atmospheric pressure

peel is then removed with brush washers

note: has largely displaced lye peeling

Food Processing Technology (6 decks)

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