PRODUCT MANAGEMENTPRODUCT MANAGEMENT

The control of temperature is the single The control of temperature is the single most important tool available to most important tool available to maintain quality after harvest.maintain quality after harvest.

Temperature management consist two Temperature management consist two phases. phases. The first is a cooling phase to remove The first is a cooling phase to remove

product field that.product field that. The second phases involves holding The second phases involves holding

the product at the optimum temperature the product at the optimum temperature during distribution.during distribution.

The lower you can hold the temperature, The lower you can hold the temperature, without causing an injury to the product, the without causing an injury to the product, the greater the effect on :greater the effect on : the rate of respirationthe rate of respiration the rate of water lossthe rate of water loss pathological activitypathological activity insect activityinsect activity growth and development after harvestgrowth and development after harvest ethylene production, and the sensitivity of ethylene production, and the sensitivity of

some tissue to an ethylene exposuresome tissue to an ethylene exposure

The Principles of Cooling The Principles of Cooling Horticultural ProduceHorticultural Produce

To ensure fast cooling and prevent To ensure fast cooling and prevent rewarming, the coolroom or cooling rewarming, the coolroom or cooling system must be able to effectively system must be able to effectively handle the heat load it is exposed to.handle the heat load it is exposed to.

The principles of heat exchange. When a The principles of heat exchange. When a substance changes from a solid to liquid substance changes from a solid to liquid or a liquid to a gas, heat is absorbed. or a liquid to a gas, heat is absorbed. When a substance changes from a gas When a substance changes from a gas to a liquid or a liquid to a solid, heat is to a liquid or a liquid to a solid, heat is evolved.evolved.

During cooling, water in the product changes During cooling, water in the product changes from a liquid to a gaseous state (water vapor), from a liquid to a gaseous state (water vapor), absorbing heat from the product. The water absorbing heat from the product. The water vapor evaporates (to an area of lower energy vapor evaporates (to an area of lower energy level-the coolroom), cooling the product.level-the coolroom), cooling the product.

The rate of cooling is determined by :The rate of cooling is determined by : the difference in temperature between the product the difference in temperature between the product

and the coolant (air, water or ice)and the coolant (air, water or ice) the amount of contact that is achieved between the the amount of contact that is achieved between the

product and the coolantproduct and the coolant the thermal conductivity of the product and the the thermal conductivity of the product and the

packagepackage

The difference in The difference in temperaturetemperature

The greater the difference in the temperature of The greater the difference in the temperature of the product and the temperature of the coolant, the product and the temperature of the coolant, the greater the rate of cooling.the greater the rate of cooling.

The cooling curve shown above, has a initially The cooling curve shown above, has a initially rapid rate of cooling but this tapers off over time rapid rate of cooling but this tapers off over time as the temperature differential decrease. For as the temperature differential decrease. For example, if the product’s temperature is 30example, if the product’s temperature is 30ooC and C and the air temperature in the coolroom is 4the air temperature in the coolroom is 4ooC, there C, there is a large temperature differential and very rapid is a large temperature differential and very rapid rate of heat exchanges, as indicated by the slope rate of heat exchanges, as indicated by the slope of the curve. As the temperature differential of the curve. As the temperature differential decrease, the rate of heat exchange slows down.decrease, the rate of heat exchange slows down.

The mechanical refrigeration The mechanical refrigeration systemsystem

The mechanical refrigeration system used in a The mechanical refrigeration system used in a coolroom is based on the simple principle of coolroom is based on the simple principle of heat exchange. That is, a liquid absorb heat to heat exchange. That is, a liquid absorb heat to change to a gas.change to a gas.

The warmed air from the coolroom passes over The warmed air from the coolroom passes over the liquid refrigerant at the evaporator. The the liquid refrigerant at the evaporator. The liquid refrigerant absorbs the heat (that is liquid refrigerant absorbs the heat (that is coming from the product and the other coming from the product and the other sources), changing the refrigerant into a sources), changing the refrigerant into a gaseous form. The refrigerant gas then passes gaseous form. The refrigerant gas then passes out to the compressor where it is condensed out to the compressor where it is condensed back into a liquid. The heat is released and back into a liquid. The heat is released and expelled outside the coolroom.expelled outside the coolroom.

Sources HeatSources Heat

During cooling, there are several During cooling, there are several sources of heat that the refrigeration sources of heat that the refrigeration system has to cope with. Theses system has to cope with. Theses include :include : Product heat (field and respiratory)Product heat (field and respiratory) Conducted heatConducted heat Infiltrated heatInfiltrated heat Other heat sourcesOther heat sources

1.1. Product heatProduct heat

Product heat is made up of two components. Product heat is made up of two components. The first is referred to as the The first is referred to as the field heatfield heat of of the product. The product’s temperature at the product. The product’s temperature at harvest will be similar too the ambient harvest will be similar too the ambient temperature . The second component of temperature . The second component of product heat is product heat is respiratory heatrespiratory heat. Different . Different products respire at different rates, therefore products respire at different rates, therefore producing varying amounts of respiratory producing varying amounts of respiratory heat. heat.

2. Conducted heat2. Conducted heat

Outside heat is conducted across the Outside heat is conducted across the walls, roof and floor into the walls, roof and floor into the coolroom. Coolrooms have insulated coolroom. Coolrooms have insulated walls and roof to minimize the walls and roof to minimize the conducted heat load. The thicker the conducted heat load. The thicker the insulation in the walls and roof, the insulation in the walls and roof, the less the conducted heat load. less the conducted heat load.

3. Infiltrated Heat3. Infiltrated HeatWhenever the door of a coolroom is opened, Whenever the door of a coolroom is opened, heat infiltrates into the coolroom. If the door heat infiltrates into the coolroom. If the door is left open for long periods, the infiltrated is left open for long periods, the infiltrated heat load on the coolroom is high. heat load on the coolroom is high.

4. Other heat sources4. Other heat sourcesOther heat sources contribute to the heat Other heat sources contribute to the heat load in a coolroom. Theses include humans, load in a coolroom. Theses include humans, electric light fittings, electrical components electric light fittings, electrical components of the refrigeration system and forklifts.of the refrigeration system and forklifts.

Selecting a cooling Selecting a cooling techniquetechnique

Room coolingRoom cooling Only products that have a low Only products that have a low to very low perishibilityto very low perishibility

Forced –air coolingForced –air cooling Fruits, fruit vegetables, Fruits, fruit vegetables, tubers, cut flowers, floral tubers, cut flowers, floral vegetablesvegetables

Hydro-coolingHydro-cooling Stems, leafy vegetable, some Stems, leafy vegetable, some fruit and fruit vegetablesfruit and fruit vegetables

Vacuum coolingVacuum cooling Leafy vegetables, some stem Leafy vegetables, some stem and floral vegetablesand floral vegetables

Package icingPackage icing Roots, some floral vegetables, Roots, some floral vegetables, stems, some leafy vegetablesstems, some leafy vegetables