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Introduction to Precooling The most efficient method to control the ripening of fruits and vegetables is to remove their field heat almost immediately after harvesting. The removal of field heat is known as precooling. Precooling is the first operation in the cold chain and is essential for produce (fruits and vegetables) as they are perishable in nature. According to National council for economic research the post harvest losses of commercial fruit and vegetable is almost upto 30%. It amounts to saying that farming community is losing almost Rs.23,000 crores annually. The main beneficiary of precooling is the grower as it allows him to sell the produce at the most appropriate time and at the competitive price. Consumers and general economy also benefit through adoption of proper post harvest handling procedures through improved shelf quality, lower real costs for fruits and vegetables through the reduction of losses and spoilage. There is considerable demand for fruits and vegetables in the domestic market and abroad. India, being the second largest producer of fruits and vegetables has the potential to minimize the post harvest losses by adopting proper post harvest technology. Realizing this, the Ministry of Human Resources Development Government of India entrusted a project to develop a mobile and a stationary precoolers to Indian Institute of Science and Rinac India Limited, Bangalore. Both the precoolers are designed and developed using indigenous technology to suit Indian conditions. Bio-Chemical Effects Fruits and vegetables are living organisms that even after harvesting have active metabolism. In addition to respiration heat, certain metabolic by-products such as carbonic acid, ethylene gas are released during the storage causing accelerated ripening with undesirable consequences to the quality. All the undesirable effects are temperature dependant, higher the temperature larger the damage and culminates in product quality degradation and shortening of shelf life. The high harvest temperature causes: *
Higher metabolic activity which results in rapid product ripening or aging Method of Precooling Fruits and vegetables can be precooled by any one of the following methods. 1.
Vacuum cooling - Simple and economical.
Mobile & Stationary Precooler Quick and uniform cooling to storage temperature of fruits and vegetables within 2 hrs of harvest can increase the storage life, quality and value of the products substantially. Using the technology from Indian Institute of Science, Bangalore, under the Govt. of India, Technology Development Mission, Rinac has introduced mobile and stationary precoolers for cooling of horticultural products at the farm level. Rinac's range includes mobile pre-cooler which can be hauled from one place to other, and stationary precooler to be located at a common point.
Stationary Precooler
Mobile Precooler Salient features of Rinac Precoolers are: - *
Rapid cooling of products Mobile Precoolers A mobile precooler is one which removes the field heat at the farm and during transit period and thus essentially consists of captive power unit, suitable refrigeration system and air distribution -system and thermal storage as optional, all mounted on a chasis of mobile unit. Why
mobile precooler? - Fruits, vegetables and flowers are seasonal hence the requirement of precooling may shift from one place to other. Under
above Indian conditions there is a need for mobile precooler having a capacity of one
metric ton of product per batch which can be located / relocated from farm
to farm and one place to other depending upon the harvest plan and needs of
small/ medium farm or co-operative society. Precooling Time The approximate precooling time required using mobile precooler for select products is given below:
Cost/Benefit of Mobile Precoolers Example: Grapes precooling Precooling capacity per batch : 1000 Kg. Total cost os grapes per batch : Rs. 10,000/- Cost of consumables * Hours of generator operation per batch : 5 hrs. Total running cost on generator per batch : Rs.250/-, at Rs. 50 per running hour. * Labour cost for loading and unloading the grapes ( Rs. I per crate) : Rs. 140/- * Incidental maintenance cost per batch : Rs. 4 Maximum cost of precooling per batch :25+140+4=Rs. 394/- Maximum cost of precooling per Kg :Rs.0.394 - 40paiseonly Benefits 3
Product wastage avoided per batch = 20% = 200 Kgs Investment cost on mobile precooler *
Generator (captive in built) : Rs. 2 lakhs Payback period *
Number of batches per day : 2 Other benefits 1.
Increase in shelf-life, quality and product value. Stationary Precooler The term "precooling " implies the removal of heat before tlie product is transported to a distant market, processed or stored. Some products are room cooled at the same room in which they are stored. In this case, cooling is accomplished over a day or more. Precooling is gradually done in a separate facility within two hours or even minutes. The room cooling is not considered' "Precooling". The principal methods of precooling are hydrocooling, forced air cooling, hydrair cooling packaging and vacuum cooling. Most cooling is done at the packaging centres. Some products can be cooled by any of their methods without suffering any or adverse effects. Commercial Hydro cooling Because of simplicity, economy and effectiveness hydro cooling is a popular precooling method. When a film of cold water flows briskly and uniformly over the surface of a warm substance, the surface temperature of the substance becomes essentially equal to that of the water. Rate of internal cooling is limited by the size shape and thermal properties of the substance being cooled. Peaches, cherries and many vegetables arc successfully hydrocooled, the more important of two are sweet corn. celesy radish and carrots. Hydrair cooling Hydrair cooling uses a mixture of refrigerated air and water in Fine mist spray that is circulated around and through stack by convection. It has the advantage of reduced water requirements, and the potential for improved sanitation. The cooling rates equal to, and in some cases better than, those obtained in conventional hydrocoolers. Commercial Forced Air cooling Products can be satisfactorily cooled by air circulated in refrigerated rooms adapted for that purpose, by forcing air through voids of bulk products. Forced air involves definite stacking patterns and bafting of stacks. Successful use of the method requires a container with vent holes placed in the direction in which the air will move. Because the cooling air comes in contact with the product being cooled, cooling is much faster than with conventional room cooling. It is observed that forced air cooling usually cools in one fourth to one tenth the time required for conventional room cooling but that it still takes two to three times longer than hydro cooling. In association with Indian Institute of Science a "three-in-one precooler" has been designed & developed. The precooler can be used as either forced air, hydro or hydrair cooler. This precooler is a boon to the growers of fruits and vegetables as they can precool all types of fruits and vegetables by using suitable cooling method viz. Forced air, hydro or hydrair. The stationary precooler is designed to cool 5 tons of product in 4 Hrs. The precooler can be stationed at a common point near the farms, to facilitate immediate precooling. Because of the uniqueness of multi method cooling the utilisation period of the precooler can be enhanced by cooling vegetables and fruits harvested at different seasons. Cost/benefit of stationary of precooler. Example:
Grapes precooling. Total precooling cost : Rs 1,580/ Precooling cost/kg of grapes : 1580/5000=0.316 paise. Benefits *
Reduction in product wastage per batch : 20% = 1000 kgs Investment cost * Total cost of the precooler for all the three methods of cooling : Rs. 35,00,000/- Pay back period:
Recommended Storage Conditions of Select Fruits & Vegetables
Technical Specifications of Precoolers
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