Precooling of fruits and vegetables.pptx

Precooling methods and machine are described in this presentation

1. PRECOOLING OF FRUITS AND VEGETABLES

2. Pre-cooled - Alive & Happy Not-Precooled Sick and Die 2/2/24 2 Pre-cooling

3. It is the prompt cooling of the commodity immediately after harvest (generally within 24 hrs of harvest), to its safe storage temperature , which aims at removal of field heat. There are different cooling methods followed for different commodities . Some fungicides may be mixed in water during hydro-cooling to reduce decay incidence Weight loss during forced air cooling can be reduced by maintaining high (95%) relative humidity in the pre-cooling chamber. 2/2/24 3 Pre-cooling

4. It removes the field heat  Reduces the rate of respiration and ripening Reduces the loss of moisture  Reduce bruise damage during transits Reduces the production of ethylene Reduces /inhibits the growth of spoilage organisms  Eases the load on the cooling system (refrigeration) of transport or  storage  chamber Above factor helps in extends the product shelf life 2/2/24 4 Purpose of precooling

5. Air temperature during  harvesting  (during summer pre-cooling time is more) Time between harvest and precooling Nature of the crop (High perishable crop require immediate pre-cooling) Difference in temperature between the crop and cooling medium Nature/Velocity of the cooling medium Rate of transfer of heat from the crop to the cooling medium. Type of package material used – Use of water proof ventilated boxes for good air circulation in the room is helpful. Plastic boxes/ fiber board cartons which have been treated with wax will render them water proof. Thermal conductivity of produce 2/2/24 5 Pre cooling depends on the following factors

6. Conduction and convection are the two main heat-transfer mechanisms used for cooling of produce. With conduction, the heat is transferred within a produce to its coldest surface. This is direct movement of heat from one object to another by direct methods (from fresh produce to water or warmer to cooler). With convection, the heat is transferred away from the surface of the produce via a cooling medium such as moving water or air. 2/2/24 6 Mechanism of pre-cooling  

7. S election of precooling methods depends on: The temperature of produce at harvest Physiology of produce Desired postharvest life Different methods of precooling: cold air (room cooling, forced air cooling), cold water (hydrocooling), direct contact with ice (contact icing), evaporation of water from the produce (evaporative cooling, vacuum cooling) and combination of vacuum and hydrocooling ( hydrovac cooling). 2/2/24 7

8. It is low cost and slow method of cooling. In this method, produce is simply loaded into a insulated cool room and cool air is allowed to circulate among the cartons, sacks, bins or bulk load. Advantages: Produce can be cooled and stored at the same room thus saves on handling costs No extra cost for pre-cooling equipment Suits for crops, which are marketed soon after harvest Disadvantages: It is too slow method of cooling Space requirements for room cooling are more as compared to storage, thus loss of storage capacity Unsuitable for packed produce Excessive water is lost from the produce due to slow cooling. Horticulture crops suitable for rooms cooling are: Potato, onion, apple and citrus 2/2/24 8 Room cooling

9. 2/2/24 9 Modified room-cooling method to enhance the precooling process of fresh produce.

10. Forced air-cooling is mostly used for wide range of horticultural produce This is the fastest method of pre-cooling Forced air-cooling pulls hot air or pushes cool air through the vents/holes in storage containers In this method uniform cooling of the produce can be achieved if the stacks are properly aligned. Cooling time depends on ( i ) the airflow (ii) the temperature difference between the produce and the cold air and (iii) Amount of the produce 2/2/24 10 Forced-air cooling

11. Advantages: Fast method of pre cooling ( upto 90% faster than room cooling) Suitable for wide range of highly perishable commodities. Uniform cooling , if produce are properly aligned. Cooling times can be controlled for different types of produce by controlling the air flow rate. Horticultural produce suitable for forced air cooling are: Grapes, Berries, Pears, Peach, Oranges, Strawberries tomato, and other tropical and subtropical fruits. 2/2/24 11

12. 2/2/24 12 Types of Forced Air Cooling

13. 2/2/24 13 Forced Air Cooling

14. Cleaning and precooling at same time The use of cold water is an old and effective cooling method used for quickly cooling a wide range of fruits and vegetables before packaging. For the packed commodities it is less used because difficulty in the movement of water through the containers and high cost involved in water tolerant containers. This method of cooling not only avoids water loss but may even add water to the commodity. Some chemicals (nutrients/growth regulators/ fungicides) can also be mixed with the water used in hydrocooling to prolong the shelf life by improving nutrient status of crop and preventing the spread of post harvest diseases. The hydrocooler normally used are of two types : Shower type and Immersion type 2/2/24 14 Hydrocooling

15. Advantages : • Less energy is used as compared to forced air cooling i.e. water removes heat about 5 times faster than air • Moisture loss does not take place. Disadvantages : • Most of the packages don’t tolerate wetting • Wax layer of some fruits like pear, plum, apple are removed by using spray type of hydrocooler Horticultural produce suitable for hydrocooling are: Mango, peach, cherry, Asparagus etc. not suitable for berries, potato, onion etc 2/2/24 15

16. 2/2/24 16 Immersion type hydrocooler

17. 2/2/24 17 Shower type hydrocooler

18. Vacuum cooling take place by water evaporation from the product at very low air pressure. In this method, air is pumped out from a larger steel chamber in which the produce is loaded for pre-cooling i.e. vacuum is created Removal of air results in the reduction of pressure of the atmosphere around the produce, which further lowers, the boiling temperature of its water. As the pressure falls, the water boils quickly removing the heat from the produce. Vacuum cooling cause about 1 per cent produce weight loss (mostly water) for each 6 ∘ C of cooling. 2/2/24 18 Vacuum cooling

19. Advantages : Fast and uniform cooling takes place. Most energy efficient method. Disadvantages : High capital cost Produce losses more moisture To overcome the more loss of water from the produce, another method of water spray vacuum is used, (modification of vacuum cooling), called hydro-vac cooling. 2/2/24 19

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21. I n some commodities, crushed or flaked ice is packed along with produce for fast cooling. However, as the ice comes in contact with the produce, it melts, and the cooling rate slows considerably. The ice keeps a high relative humidity around the product. Liquid icing distributes the ice throughout the container, achieving better contact with the product. Packaged icing can be used only with water tolerant, non-chilling sensitive products and with water tolerant packages (waxed fiber board, plastic or wood) 2/2/24 21 Top icing

22. 2/2/24 22 Continuous application of ice to produce cartons.

23. 2/2/24 23 Manual injection system for icing produce cartons.

24. Evaporative cooling is based on the thermodynamics of evaporation of water, i.e., the change of the liquid phase of water into water vapor. This phase change requires energy. This energy comes from the internal energy of water, which is the latent heat of the evaporation of water. Evaporative cooling uses evaporation to help cool the air. Based on the principles of evaporation, hot and dry outside air is drawn through water-soaked cooling pads. As the air is pushed through these pads, the water evaporates and the heat in the air is absorbed, which lowers the air temperature. 2/2/24 24 Evaporative cooling 

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26. Based on the principle of direct evaporative cooling zero energy cool chambers have been developed. The main advantages of this on-farm low cost cooling technology are: 1. It does not require any electricity or power to operate 2. Materials required like bricks, sand, bamboo etc. available easily and cheaply. It is a double brick-wall structure, the cavity is filled with sand and walls of the chamber are soaked in water. Even unskilled labour can build the chamber, as it does not require any specialized skill. Cool chambers can reduce temperature by 10-15 ∘ C and maintain high humidity of about 95% that can increase shelf life and retain quality of horticultural produce. Small and marginal farmers can store a few days' harvest to avoid middlemen. Technology Vision 2020 has identified it as a low cost storage technology for 2020. National Horticulture Board is giving 100% grant in aid for the benefit of the farmer. 2/2/24 26 ZECC ZECC

27. Select an-upland having a nearby source of water supply. Make floor with brick 165 cm x 115 cm. Erect the double wall to a height of 67.5 cm leaving a cavity of 7.5 cm. Drench the chamber with water. Soak the fine river bed sand with water. Fill the 7.5 cm cavity between the double walls with this wet sand. Make top cover with bamboo (165 cm x115 cm ) frame and ' sirki ' straw or dry grass. A thatch/ tin shed made over chamber to protect from direct sun or rain or snow. 2/2/24 27 Construction

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30. All precooling processes display analogous performances. Following an initial “lag” period the temperature at the thermal center of the produce item decreases exponentially. A typical precooling curve illustrating this behaviour can be obtained by plotting the ratio of the unaccomplished temperature difference, Y, against time on semilogarithmic axes in relation to the total temperature change possible for the cooling condition. The fractional unaccomplished temperature difference, Y, is expressed as follows: = where T is the temperature at a given time, °C; T i is the initial temperature, °C; and T m is the cooling medium temperature, °C.   2/2/24 30 Rate of Cooling

31. 2/2/24 31 Cooling Curve