4. Cleaning, sorting, grading Flashcards
what is cleaning
preliminary operation to remove contaminants from raw materials that will be processed
purpose of cleaning
remove contaminants, from innocuous to hazardous
a. for the sake of final consumer (safety)
b. protecting processing equipments
what to consider in the cleaning stage
- higher possible efficiency of contaminant removal
- ratio of energy input and % of contaminants removal - minimal loss or damage to raw materials being cleaned
- minimizing bumping, cracking, other measn causing physical damages - precautions avoiding recontamination after cleaning
- arranging process flow to avoid cross contamination
cleaning methods based on application of water
- dry cleaning
(screening, brushing, aspiration, magnetism, electricity) - wet cleaning
(soaking, spraying, fluming, flotation)
advantages and disadvantages of dry cleaning
(+)
- low cost
- convenient
- surface left dry
(-)
- spread of dust
- risk of recontamination
-dust explosion hazard
careful control of dust methods
- dust proofing equipments
- removal of dust by gas-solid separators (cyclones, rigorous housekeeping, etc)
advantage and disadvantage of wet cleaning
(+)
- highly efficient for soiled raw materials (eg fruits, vegs, tubers)
(-)
- large quantity of high purity water required
- large quantity of dirty effluent produced
principles of screening
- used to remove contaminants of CONSIDERABLE DIFFERENT SIZE from food being treated
- usage of size separators based on perforated beds or wire mesh
two methods of screening
- scalping
raw material pass through screen, contaminants retained - de-dusting
raw materials retained, contaminants pass through screen
examples of devices used for screening
- flatbed screening unit
- one or more flat sieve decks fixed in a dust tight casing
- shaken by different devices - rotary screen
principles of aspiration
- 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
principles of magnetism
- removal of ferrous metal using permanent/electromagnets
- particulate foods passed over magnetized drums or conveyor belts; powerful magnets located above conveyors
application of aspiration
cleaning cereals, peas, beans
source of metal contaminants
- growing field
- picked up during preliminary operations
principles of electricty cleaning
- 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
why should wash time be kept to minimum
washing after pee;ing/cutting/pitting may results in loss of soluble components (sugars, vitamins, minerals0
benefits of cold water in wet washing
- 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
factors affecting efficiency of wet cleaning
- amt of washing water
- temperature
- force applied
- acidity (may retard enzymatic activity)
- mineral content (Ca) may dislodge bacteria from surface
how to improve soaking efficiency
- move water relative to product or move product relative to water
- sparging compressed air
common wet cleaning/washing methods
- belt conveyor by sprays of water
- roller conveyor by sprays of water (for berries and other soft fruits)
- rotary washers (with thin rods or wire mesh at which debris can fall through)
- flotation washers (with water recirculation, commonly used for peas)
- brush washers (with cylindrical rotating brushes, used for root crops)
how does combo washing machine work
dry soil removal, water saving, gentle washing and stone rmoval
(version without dry soil/stone removal possible)
advantage of combo washing machine
- low water consumption
- good washing results, even for soil and clay
- low operating costs
- dry preliminary soil removal
- continuous, reliable stone removal
difference between sorting and grading
sorting: takes into acc one quality attribute only
grading: takes into acc combination of quality attributes
principles of sorting machines
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)
