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64 Cards in this Set
- Front
- Back
why is 28 F considered refrigeration if water freezes at 32F
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thats the freezing point of water but there are solutes, fats etc
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bacteriostatic
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mesophile
keep chilled, prevent growth (freezing, fridge temp) |
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bacteriocidal
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can kill organisms
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soda holds more gas as??
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it cools, increased CO2 solubility
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cooling
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removing heat vs. putting in refer
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when should cooling begin
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immediately at harvest or slaughter
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what happens with corn that loses sweetness?
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doesnt change nutrition, just sweetness bc enzymes are making sugars into starch
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heat removal of leafy vegetables
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spray with cold water
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heat removal of produce
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cold air from evaporating liquid nitrogen can be used
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heat removal of bulk liquids
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heat exchangers: use cold water, glycol or brine
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heat removal with carcasses
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cold air in refrigerated area
-convection ice bath: conduction |
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gentlest form of food processing
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refrigeration/cold storage
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is wet or dry heat more effective for killing pathogens, why?
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wet because heat moves through water faster than dry air
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starches thickening later etc
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can keep them in convection mode longer now because they can thicken upon cooling
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freezing methods
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1. freeze in air
2. freeze by indirect contact with refrigerant 3. freeze by direct contact immersion in refrigeratn |
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explain same product but different cultivars
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company supplies seeds, not as many choices bc of quality
-commercialization of agriculture and loss of farmers choice |
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freezing process
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1. area closest to cold source freezes firt
2. water first 3. concentration of solutes...harder to freeze the rest |
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what happens when water super cools?
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< 32 F
-disturbance leads to crystallization -can be liquid below freezing |
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changes due to freezing
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1. textural
2. break emulsions 3. denature proteins 4. colloidal suspensions 5. dehydration 6. ice crystals |
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explain freezing change in texture
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rupturing of cells, loss of turgor
-leads to precipiation of solutes, conc effect |
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explain denaturing of proteins during freezing
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solutes that concentrate but don't ppt, salt out
-acidic solutes become conc, drop pH, isoelectric pt issue |
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isoelectric point
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pH of minimum solubility...coagulate
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explain colloidal suspensions with freezing
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concentration of anions and cations leads to loss of suspension. ppt out
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explain dehydration with freezing
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water freezes
concentrates solutes water gradient water moves and dehydrates |
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explain ice crystals and freezing
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cells can be ruptured by crystals
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ice cream slow freeze =
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loss of volume
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BTU
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british thermal unit
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calorie
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amt of energy it takes to inrease 1 g of water 1C
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specific heat
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amt of atp it takes to increase a pound of water by 1F
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specific heat with calories and BTUs
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BTU: 1 lb food 1F
cal: 1 g food 1C |
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tons of refrigeration
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number of BTU's it takes to convert 1 ton of water at 32F to 1 ton of ice at 32 F
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144 BTU = ??
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1 lb/1F
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how can you decrease spoilage enzymes even more than just doing the -18C
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blanch them before freezing
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heat removal needed to maintain room
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1. door openings
2. personnel 3. respiration: minimal |
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determining amt of refrig needed in freezing
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1. heat removal before freezing
2. heat related to freezing process (latent heat of crystallization) 3. heat related to heat removal to get to desired temp |
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issues with freezing in air
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1. if unwrapped...
-lose moisture during freezing and -lose moisture during frozen storage 2. freezer burn |
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freezing in air issues are accelerated by
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blast freezer
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sublimation
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frozen water changing to gas w/o going to water state
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still air freezing, conduction or convection
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conduction
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two things you have to do for freeze in air
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1. change temp of air
2. change velocity of air |
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most efficient heating or cooling method
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countercurrent flow
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how do you choose still or agitated retort
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based on the type of food being processed
-size matters |
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how does a tubular heat exchanger work
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1. scrapers will most of internal area
2. forces food to outer region so its in contact with cold surface 3. scrapers keep cold surface free of layer of frozen product 4. scrapers remove any ice crystals which form 5. scrapers keep product moving through the tube, no freezing tube solid |
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what happens when teh scrapers remove the ice crystals
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they go into the food and act as seeds for further freezing of the product
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why are meat/fish cooled more efficiently than vegetables and shrimp?
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larger surface area
-vegs and shrimp might have air pockets in between that serve as insulation |
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pasteurization
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requires that every particle reaches the required temp for the required length of time
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pasteurization is a heat treatment that will...
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kill human pathogens present in a product but not all orgs or spore formers
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how is z value determined
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1. plot D value v temp
2. draw best fit line 3. determine change in temp to get 1 log drop |
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what is the practical value of the z-value
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allows us to determine how long it would take at a temp we never tested
-make determinations on preocessing based on theoretical kill b product degradation that would occur at a given temp |
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why frozen foods
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1. save money, get more food
2. allows for long distance travel of foods 3. convenient 4. eliminate prep time 5. thawing/cooking only thing left and you can do them at the same time |
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how do you determine amt of refrigeration required?
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1. heat from produce/food to reduce it to desired temp
2. heat of respiration during storage 3. heat loss due to door opening/ppl 2F 4. loss due to insulation properties of the cooler, efficiency |
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functions of heating
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1. change sensory props, more palatable
2. change flavor/chemical make up 3. decrease mic load -sterilization: veg cells killed easily but not spores Spores: 121 C wet heat 15 mins, retort -can take a long time, degrades, every part treated to proper time temp 4. inactivate nat enzymes 5. inactivate heat labile toxins |
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refrigeration v freezing
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Refrigeration
-spoilage issue, psychrotrophs -some pathogens, list mono -slows enzymatic degradation -short term storage, days to few weeks Freezing: -greatly decreases microbial spoilage -prevents GROWTH of pathogens -storage time greatly increased, months to years: FIFO |
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must release P in retort slowly to prevent?
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1. cans imploding
2. jars bursting 3. flexible pouches from bursting |
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continuous retorts you must
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regulate the rate at which the product moves from pressurized situation to atmospheric pressure
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still/batch retorts you must
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regulate teh rate the steam is dissipated
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retort loaded...pressure applied =?
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steam
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what happens when moisture in the food starts to vaporize
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builds up pressure equal to the pressure in the applied steam
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when is after pkging in package pasteurization used
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beer...140F...will get killing of spilage microorgs but not overly affect the flavor
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how is direct flame used with after pkging in pkg pasteur
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pass cans directly over gas jets
-not used much |
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after pkg in pkg pasteurization typically runs at ?? P??
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atmospheric pressure
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does after pkg in pkg pasteurization result in sterile or commercially sterile food
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no
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after pkg in pkg pasteurization is gentle on>>?
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glass containers
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after pkg in pkg pasteurization typically uses?
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steam or hot water jets to heat the product
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