Qual Review of Food Processing

What is food processing?

Food preservation method, creates functionality, and increases nutrition

Why is scale important? What is scale up?

This is very important for having to feed over a million people. A scale up is increasing the production from a benchtop to a pilot plant scale to an industrial scale. This has a big effect on mass production including the overall cost (reduction) and quality control

What is a unit operation?

It is a basic step in an operation

What are some examples of unit operations?

Evaporator, storage tanks, filler, shipping, peeler/dicer, washing, mill, pasteurizer, grinding, extraction, drying

What are the five classes of unit operations?

Fluid flow (fluids transportation, filtration, solids fluidization) heat transfer (canning, freezing, blanching) Mass Transfer (extraction, dehydration, frying) thermodynamic processes (gas liquification, refrigeration) Mechanical processes (solids transportation, crushing and pulverization, screening and sieving)

What is mass balance? Why is it important?

Input-output=accumulation, and in a steady state process accumulation = 0 so: mass in =mass out

What is the difference between total mass balance and individual mass balance?

There is a balance equation for each component and then there is a balance that takes everything into account. For example if a unit like apples involves 3 components (sugar, water, solids) then you will have 3 independent mass balances and one total mass balance

What is the importance of evaporation?

One of the big reasons is that we want to minimize the material that we have to ship, for example orange juice, you can ship a lot more as concentrate than as juice, saving lots of money on shipping and space for storage.

What is the mechanism of evaporation?

Evaporation is an endothermic process (gets colder as it reaction goes on), evaporation lowers the temperature because the higher moving faster (hotter) molecules are being removed. Cohesive forces keep molecules together, and evaporation is the escape of those molecules

How does vapor pressure effect evaporation?

Water will naturally evaporate into the air until the rate of evaporation = the rate of condensation

How is boiling point linked to evaporation?

Boiling point is the temperature at which the vapor pressure of the liquid is equal to the external pressure

How does elevation effect boiling point?

As altitude increases the air pressure (external pressure) decreases, therefore at higher elevation the air pressure is less so the boiling point lowers. This is important in the food industry because if you want to minimize quality degradation then evaporation should take place at higher elevations where it doesn't have to reach as high of a temperature to achieve the same effect.

Why do bubbles form in boiling but not during evaporation?

Bubbles can't form in evaporation since the vapor pressure is less than the atmospheric pressure. Bubbles DO form in boiling because the vapor pressure can overcome the atmospheric pressure.

What is a steam table? What is it used for?

A steam table gives different boiling point and what the vapor pressure has to be to achieve boiling (local pressure=vapor pressure at boiling) and then what the enthalpy of liquid vapor and liquid is at that temperature and you can subtract the two to get latent heat. It is used to find the boiling point at different pressures and also the amount of energy needed for vaporization at that point.

How do you get latent heat from the steam table?

You take the enthalpy of saturated vapor minus enthalpy of liquids, or there will be a column enthalpy of evaporation which is equal to latent heat

What is latent heat of fusion?

Temperature remains constant as solid turns to liquid

What is latent heat of vaporization?

Temperature remains constant as liquid turns to gas

What does a gauge tell you?

A gauge can only tell you the difference between the pressure it is measuring and the atmospheric pressure.

What is Gauge pressure?

Positive difference between atmospheric pressure and absolute pressure, measures pressures greater than atmospheric pressure

What is vacuum pressure?

Negative difference between atmospheric pressure and absolute pressure, measures pressure less than atmospheric pressure

What is absolute pressure?

It is the atmospheric pressure + Gauge pressure or - vacuum pressure.

What is industrial evaporation?

Boiling

What are the 4 purposes of evaporation in industry?

To reduce the volume of the product, to economize on packaging, shipping storage and distribution costs. To pre-concentrate liquid foods such as fruit juice, milk and coffee before product enters a dehydration process, thus saving energy in subsequent operations. To increase solids content of food and hence preserve it by lowering water activity. To reduce the microbial load and stabilize the product

What are the three heat transfer modes?

Convection - flow of air or water over a physical body, maintains large gradient. Conduction - direct transfer between two physical bodies (surface area, gradient, heat, conduction) . Radiation - transfer of heat between two physical bodies that are not in direct contact with each other. (Evaporation) - liquid becomes gas (heat loss), release of energy in the form of heat

What is the equation for conduction and how can you reduce evaporation time?

Q=KA[ΔT/L) where Q equals the heat rate, K is thermal conductivity, L is thickness of wall, A is surface area of the wall, ΔT is the difference in temperature between two sides. When you increase the area you increase A and reduce evaporation time, also when you increase the temperature difference you increase Q and reduce evaporation time

What is the equation for convection and how can we effect heat transfer?

There are two mechanisms - random molecular motion (diffusion) and bulk motion of the fulid (when velocity = 0 only diffusion, when velocity ≠0, diffusion + bulk motion). Equation : Q=Asteam hsteam(ΔT) then conduction through wall then Q=Ajuice hjuice(ΔT) where h is the convective heat transfer coefficient. Relationships: as increase velocity of the fluid, then decrease the boundary layer, then increase the heat transfer coefficient, and increase hear transfer rate. If increase viscosity, then increase boundary layer and decrease heat transfer coefficient and decrease heat transfer rate.

Why do we care about the heat transfer rate (Q) ?

Because if we increase heat transfer than we decrease residence time, and increase the capacity, this lets us reduce capital investment and increase profit. Also if decrease residence time then you will decrease quality degradation

What is the overall heat transfer coeffiecent?

Q=Asteam hsteam(ΔT) then conduction through wall then Q=Ajuice hjuice(ΔT) where h is the convective heat transfer coefficient , can combined and get Q=AU(Tsteam-T) where U = overall hear transfer coefficient, it is a combination of conduction and convection (convection heat transfer coefficent and thermal conductivity)

How do natural and forced circulation affect the boundary layer?

Natural circulation has laminar flow and an increased boundary layer, and forced circulation is turbulent flow and therefore decreases the boundary layer

How do soluble solids affect the boiling point and freezing point of a solution?

When a solute (soluble solid) is added it lowers the vapor pressure above the solution therefore causing boiling point elevation because more vapor has to be created to overcome the atmospheric pressure and it also causes freezing point depression

What does the Bernoulli equation allow us to calculate?

It allows us to find the pressure at a particular height

How are the units: inches of mercury, atmosphere, pascal and psi (pound per square inch) related?

1 atm = 760 mmHg = 30in HG = 101,325 Pa = 14.696 psi

What is the definition of an evaporation?

A device wherein liquid is evaporated from a thin (low concentration) feed material in order to produce a more dense or thick product (concentrate). The feed may be a solution, slurry, or suspension of solid material in a liquid. The hear necessary for vaporization is supplied through heat transfer across metallic surface by condensing steam.

What unit operations take place during evaporation?

Thus evaporator operations basically involve energy transfer (heat for vaporization and condensation), mass transfer (moisture removal), fluid flow (feed and vapor flow)

What are the different types of evaporators?

Batch pan, tubular evaporators (natural circulation, rising film, falling film, rising falling film, forced circulation evaporator, agitated thin film [wiped film]) plate evaporators ( rising falling, falling, parvap, paraflash

What is the batch pan method, how does it work, what is it used for?

Oldest method of evaporation next to solar evaporation, heating of sample using jacket or internal coils, it has high residence time (many hours). Still used to make jams and jellies

What is the natural circulation tubular method, how does it work, what is it used for?

Utilizes the density difference between the liquid and the generated vapor to circulate the liquid past the heating surface. It is a continuous process and the residence time is 10-20 minutes. It is used for cane sugar solutions

What is the rising film tubular method, how does it work, what is it used for?

This is the first modern type of evaporator, the forming of vapor bubbles inside the tubes causes a pumping action giving high liquid velocities. Residence times are low, hear transfer coefficients are high and hence heating area is reduced and initial capital is lowered. Need at least 25F temp difference to establish a well developed film. It is used for condensed milk.

What is the falling film tubular evaporator, how does it work, what is it used for?

Going with gravity instead of against it, this results in thinner and faster moving film and gives rise to shorter contact time and further improvement in the heat transfer coefficient. The key technical hurdle is the even distribution of liquid to each of the tubes

What are the two types of distribution systems for falling film evaporators?

Static distribution system (bowl with smoothing plate) and dynamic distribution system (liquid distribution by means of a full cone nozzle)

What is the rising-falling film evaporator, how does it work, what is it used for?

Combines the previous two, the purpose is to save headroom, about half the height of the previous two methods

What is the forced circulation evaporator, how does it work, what is it used for?

This is for viscous fluids, liquids with suspended solids and some degree of scaling and fouling. Product is pumped at high velocity through a heat exchange section where boiling is prevented by the application of hydrostatic pressure. High velocity helps to prevent scaling and fouling and to increase heat transfer rate, absence of boiling also helps reduce scaling, capital investment and operation cost high

What is the agitated think film tubular evaporator, how does it work, what is it used for?

For very viscous foods, feed is spread on the inside of the cylindrical heating surface by wiper blades, small heating area and high cost.

What are the plate type evaporators that are used?

Rising film, falling, parvap (similar to wiped film) and paraflash (similar to forced circulation)

What factors do you need to take into consideration when doing evaporator calculation?

Mass balance equations (total balance, solute/solid, water, evaporation rate, feed rate) energy balance (energy input from steam, energy consumed by evaporator)

What is vapor recompression?

to increase the pressure and temperature of the vapor to be used again in evaporation

What is thermal vapor recompression?

As a way to reduce energy consumption a thermocompressor which uses high pressure steam as a motive fluid is added to a typical steam heated evaporator. The motive steam at approximately 150 psig enters the thermocompressor and expands as it passes through a diffuser=

What is mechanical vapor recompression?

Use compressor to increase pressure of vapor to increase energy efficiency. Mechanical energy supplies via a compressor or fan compresses the process vapor to a higher pressure (and condensing temperature) where it is reused as the heating steam

What is the multiple effect design?

Where vapor from the previous evaporator is used to evaporated more water from the concentrate in the next evaporator. utilizes the latent heat of the vapor

Compare thermal vapor recompression to mechanical vapor recompression

$ Vapor compressed Energy savings Draw-back TVR Low A fraction One effect MVR High All ≥ 15 effects Noisy

What is freeze concentration?

Freeze concentration is fundamentally a crystallization and separation process. It involves partial freezing of product and removal of ice crystals.

What is the point on the phase diagram where ice crystals and sugar crystals form?

It happens at the eutectic temperature

What happens to the freezing point as ice is removed?

As water is removed from the system and the concentration of solids increases and the freezing point of water decreases.

What are the steps in freeze concentration?

Step 1: It all starts from the ice crystal point of view by removing heat from the solution, Typically done by using a scraped surface heat exchanger ( inside scraped by a rotating shaft while outside cooled by refrigerant). Tiny ice crystals are formed at this cold surface. Step 2: Once crystals formed in SSHE, enter a mixed vessel (recrystallizer). Most of the small crystals will melt allowing larger ones to grow. Why? Bc melting required the addition of heat and changing from solid to liquid. Known as ripening and forms the heart of separate nucleation and growth process. Step 3: Since we want a continuous flow of small crystals to the recrystallizer, we must extract liquid from a filter in the recrystallizer and circulate that over the SSHE (scraped surface heat exchanger). Step 4: Once sufficient crystals in recrystallizer can start separation from concentrated liquid, This is done with wash column, where crystals sep from liquid, washed to remove and remaining concentrate, melted and discharged as pure water, Concentrate returned to recrystallizer. Step 5: Fresh feed replaced the water that is removed from the system. The feed is mixed with the recirculation stream feeding the SSHE. Since the feed is replacing the water that is removed from the system the concentration of the soluble solids in the system will increase. Step 6: Next add a way to remove the concentrated product, discharged from the liquid recirculation line after filtration. Since the concentrate contains all of the soluble solids originally in the feed the system will now remain constant

Why are the first small crystals remelted and recrystallized in freeze concentration?

Bc melting required the addition of heat and changing from solid to liquid. Known as ripening and forms the heart of separate nucleation and growth process

What are the different types of freeze concentration units?

Ice Crystallization (Direct contact freezers, Indirect-contact freezers) and Separation Devices (Mechanical press, Centrifugal, Wash column)

What are the advantages of freeze concentration?

Freeze concentration operating at subzero and is a closed system: No loss of aromas or other volatile components, Retention of all sensory properties of the original feed product, No thermal degradation, Minimized oxidation, No loss of solids, The process is specifically interesting for the treatment of heat sensitive substances and for all applications where maximum retention of a product quality is a key aspect

What are the limitations of freeze concentration?

High cost, Difficulty in separation of ice from solid, Low upper limit on concentration, Has no effect on enzymes and microbes

What are some of the applications of freeze concentration?

coffee, citrus, juices, beer, wine, vinegar, dairy products, meat/fish extracts

What two types of equipment achieve powders as end products?

Spray and freeze dryers both achieve powders

What is membrane separation?

A membrane is a thin barrier which allows selective passage of different species through it. This selectivity is utilized for separation. The membrane process is based on pore size

What are the factors that affect the selectivity of membrane separation?

size, shape, electrostatic charge, diffusivity, physiochemical interactions, volatility, polarity/solubility

What are the driving forces of membrane processes?

Transmembrane pressure, concentration gradient, chemical potential, osmotic pressure, electric field, magnetic field, partial pressure, pH gradient

What are the steps of membrane separation?

Feed enter, permeate penetrates the membrane, retentate is what doesn't pass through) reject, concentrate, residue)

What are the different ways to set up membrane filtration?

Batch operation, continuous operation (single pass , feed and bleed)

What is conventional filtration?

perpendicular flow causes a quick buildup of solids on membrane surface and reduces flux

What is tangential flow filtration?

increases permeate passage through the membrane, greatly improves efficiency

What are the types of membranes used in membrane separation?

microfiltration, ultrafiltration, nanofiltration, reverse osmosis

What is microfiltration?

Particles retained 0.02 - 10 mm, Pressure 1-50 psig, Bacteria, fat globules (suspended particles) rejected, Applications: dairy (milk - removal of bacterial and spores, fractionation of proteins), egg (remove bacteria) juice (clarification) Beer (recover yeast)

What is ultrafiltration?

Particles retained 0.001 - 0.02 µm, Pressure 10-100 psig, Proteins rejected (macromolecules)

What is nanofiltration?

Pressure 20-40 psig, Sugars divalent salts, dissociated acids rejects, Water and small univalent ions can pass

What is reverse osmosis?

Pressure 200-300 psig, Reject monovalent species and undissociated acids, ONLY WATER can pass!

Discuss membrane concentration of liquid foods.

Based on ability of semipermeable membranes of appropriate physicals and chemical nature to discriminate between molecule primarily on the basis of size and to a lesser extent on shape and chemical composition. A membranes role is to act as a selective barrier enriching certain components in a feed.

What is electrodeionization?

removes ions and charge

What is pervaporation?

this coupled with biomass fermentation process for bioethanol production

What are the different types of membrane materials available?

polymers most common, inorganic more stable. Synthetic membranes : PVC. Polymeric membranes: widely used for UF, wide tolerance to pH temp and chlorine. Ceramic membranes: made from mineral materials such as glass aluminum oxide, and zirconium oxide, expensive and can be brittle, mainly for MF. Glass membranes. Metallic membranes: ability to withstand extreme chemical and thermal stress. Zeolite membranes: a solid with lots of tiny holes. Can have different selectivity, long term stability at high temp resistance to harsh environments and high pressure drops. Inertness to microbial degradation and easy cleanability and catalytic activation

What are the different membrane module selections?

Flat sheets - can wrap into different shapes, Plate and frame module - feed fed through spacer(between membranes) and permeate moves through membrane, Spiral module - product flows through center and then permeate moves outward through membranes, Tubular >10mm tubular, Capillary 0.5-10mm, <0.5mm hollow fiber

What are the advantages & disadvantages of flat sheet/plate and frame membrane modules?

Advantages: Low hold up volume, Permeate from individual membrane element, Membrane replacement easy Disadvantages: Difficult to clean, Susceptible to plugging

What are the advantages and disadvantages of spiral membrane modules?

Advantages: Compact, Minimum energy consumption, Low capital/opening cost Disadvantages: Not suitable for very viscous fluid, Dead space, Difficult to clean, Faulty membranes - change whole module

What are the advantages and disadvantages of hollow fiber membrane modules?

Advantages: Low hold up volume, Back flushing possible, Low energy consumption Disadvantages: Susceptible to end-face fouling, Not suitable for viscous fluids, Single fiber damage - replace entire module

What are the advantages and disadvantages of tubular membrane modules?

Advantages: Feed stream with particulate matter can be put through membrane, Easy to clean Disadvantages: High energy consumption, High hold up volume

What are brix?

Brix = g solids / total solution g (Solids + solvent)

What is food dehydration?

A unit operation in which water activity of a food is lowered by removal of nearly all the water normally present through vaporization and or sublimation. A process of thermally removing volatile substances (moisture) to yield a solid product. One of the oldest and most common unit operations found in diverse process.

What do we dehydrate food?

extend shelf life, quality enhancement, ease of handling, packaging, handling, transportation

What is the difference between dried food and dehydrated food?

Dehydrated food has no more than 2.5% water on a dry basis and dried food could be more than 2.5% dry basis

What are some of the external conditions that affect drying?

Humidity, relative humidity, are velocity, dry bulb temperature, wet bulb temperature, dew point temperature, specific volume, enthalpy, geometry of the food

What are some of the internal conditions that affect drying?

properties of food, thermo conductivity, density, porosity, aw, sorption isotherms

What is humidity (absolute humidity)?

H= (mass water (kg))/(mass dry air (kg))

What is relative humidity?

RH Φ=(mole fraction water)/(mole fraction water saturated )100=(pressure h2o vap)/(press sat h2o vap)100 how close the air is to saturation

What is dry bulb temperature?

temp of air measure with thermometer freely exposed to air

What is wet bulb temperature?

temperature of air measured by a thermometer whose bulb is covered by a wet cloth

What is dew point temperature?

temp at which air becomes saturated with moisture (RH=100%) and any further cooling results in condensation of water form air

What is the psychometric chart?

A chart that relates all of the external conditions to each other. If you know two conditions you can determine the other two

What are the applications of the using the external conditions in drying?

Heating air, constant humidity → ; Cooling air, constant humidity → ;Cooling below Tdew →H, ↓ along dew point line ; Drying: constant enthalpy process (WB lines)

What is water activity?

Water activity aw=(P h2O vapor in food)/(vapor pressure pure H2O@same T)= (RH%)/100

What is moisture content (dry vs wet basis)?

all calcs need to be done dry basis x=Xw/〖1-X〗w , X_w=(mass water)/(mass of moist food)*100,X=(m water)/(m dry solid), Web basis is = (m water)/(m moist food (total mass)) x 100

What is equilibrium moisture?

Xe, moisture of a food when it reaches equilibrium with the air. When it reaches this it cannot be dried anymore, free moisture= moisture - equilibrium moisture

What is a sorption isotherm?

relationship between equilibrium moisture and water activity, 3 regions: Strongly bound water/monolayer(enthalpy>>pure h2o, unfreezable at -40C, not available for chemical reaction), multilayers (enthalpy of vap>pure h2o, available as a solvent), free water in struc(available for m/o growth, enzyme activities)

How so you measure sorption isotherms?

gravimetric (weight changes), manometric (vap press changes), hygrometric(eq RH determined)

What is the application of sorption isotherms to drying?

determine Xe, limit of hot air drying