Horticultural produce begins to deteriorate as soon as it is harvested. It begins to lose its flavour and texture, and it is susceptible to infection by pathogens. An effective method of slowing the loss in quality is to cool the produce as soon as possible after harvest.
Many crops, such as pome fruits, asparagus, broccoli, peas and beans can be cooled within half an hour or so by drenching them with chilled water in a device known as a hydrocooler. This system uses 10 kilolitres per tonne of vegetable and is also very energy inefficient with no proper control system. It is estimated that 5000 tonnes of vegetables with an ex-farm value of $7 million are grown in the greater Melbourne area including Werribee south, Mornington Peninsula and the Yarra Valley.
This project is designed to overcome these issues by developing an existing cooling system that recycles and conserves water and is simple to build, using less than 0.1 litres per tonne.
The hydrocooler that incorporated water recirculation was developed and built jointly by Victoria University and Wobelea Pty Ltd. The strategy of recirculating water has reduced the water consumption from a required 60,000 litres per tonne of broccoli cooled to about 75 litres per tonne. When round fruit such as apples are cooled the water consumption is estimated to be about 35 litres per tonne.
The electrical running cost is estimated to be 20 kWh and 16 kWh per tonne of produce when the throughput is 4 tonnes per hour and 6 tonnes per hour respectively. If the water were not
recirculated the running cost would be about 300kW per tonne. This may be regarded as being infeasible.
The hydrocooler is presently located in Wesley Vale in Tasmania where it is being used to cool broccoli. Its throughput is averaging 500 bins per 46 week and each bin contains 400 kg of broccoli, and over the present three-month season 6000 bins will be cooled. The hydrocooler has sparked commercial interest amongst local growers.