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Fruit drying

The challenge

To dry or semi-dry fruit, to very specific finished moisture content, gently and efficiently, without spoilage or damage.

The solution

From small scale minimally powered installations, to integration with existing systems, SVPro Fruit drying solutions are cost effective, efficient and effective. 

Smarter processing to improve quality and processing times

"industrial food drying practices could benefit from the use of solar thermal drying... the use of those devices could cut down labour costs and production time, thus making such productions more cost effective and rewarding" - Solar food processing (Braz)

"drying of sour cherries was carried out... with constant airflow velocity of 1 m/s. Results showed air temperatures had significant effect on drying time and organoleptic properties...  It reduced drying time up to 80% and energy saving was approximately 83% in comparison with no treatment samples" - air treatment sour cherry processing (Gazor et.al.)

Aerating and drying fruit produce: sizing a SVPro system

Drying aeration is the practice of moving air through fruit, with the intention of reducing moisture content.  When done so, for each fruit taken from and to specific moisture contents, deterioration can be prevented and produce stored for longer periods.  Spoilage losses are caused by mould growth and insect activity, which is related to the moisture content and temperature of the produce in storage.

As the fruit produce dries, the process of drying aeration greatly improves its "storability" by maintaining uniform temperature throughout the storage: reducing mould development and insect activity, and preventing moisture migration.

To dry fruit produce using aeration, airflow rates should ideally be no less than 50m3/h/tonne, and preferably more than 70m3/h/tonne.  Snap drying rates can be as high as 120m3/h/tonne, and sometime in excess of this for specific finished products.

System design is based on a number of factors, including the amount of moisture to be removed, the timeframe, and the volume of fruit to be dried.  To ascertain preliminary system sizing, calculate the desired moisture reduction, and consequent weight reduction, for a given quantity of produce.  For example:

figs, from harvest 75% to finished 26%, 1000kg: finished weight 468kg.

Around 0.7kWh of energy is required to remove each litre of moisture.  For this example, that equates to 760 kWh.  To dry over 12 days requires 62kWh/day.

Average solar insolation levels in Australia vary by season, and in many fruit growing and riverland areas between 2-8kWh/m2/day.  We’ll assume 3kWh/m2/day, which implies a collection area of a little over 20m2.   

 

A single SVPro module has a collection area of approximately 2m2, so ten modules will be required.  Fans with a volume and back-pressure rating suited to the method of drying must then be selected, and ducting included.  Additional options include temperature and humidity controllers, zone monitors, flow control and check valves, each of which must be matched to the system.