For Dehydration of raw onions, they are loaded into large curing bins, where excess moisture is removed by passing large volumes of heated air (38oC) through the onions. Curing conditions the onions so that peeling and processing can be accomplished successfully.
After curing for 48 to 72 hours, the onions are passed into the processing line. Then they are carried to the preparation line. Machines automatically remove any tops that may remain attached to the onions. They are then inspected, washed in a high-pressure washer, soaked in a stainless steel tank to remove sediment, washed again in a high-pressure washer, and re-soaked in a bath of highly chlorinated water in order to reduce bacteria to the lowest possible level.
Then the onions are cut into uniform slices, which are then passed to the dryer. Here, the onions are carefully transferred to the dryer conveyor for the first stage of drying. This is the most critical stage; where, under high-volume air flow conditions and with moderately high temperatures, the bulk of the water is rapidly removed from the onion. The moisture content of the onion is reduced from an initial 83 percent to 25 percent( “A” Stage).
Close air volume and pressure control must be maintained in all parts of this drying stage as the air moves up and down through the bed to obtain product drying uniformity. At the proper point in the drying process, the onions are automatically transferred to the second stage (“B” stage) of drying; where, under reduced temperature conditions and deeper bed loadings (approximately 30 cm), the difficult to remove diffused water is slowly withdrawn. Here, moisture content is reduced 10 percent.. Moderating temperatures and air flows are used to maintain the low product temperature required for maximum product quality. After leaving the “C” stage, moisture content is down to 6 percent.).
After drying, the onions are passed over a long stainless steel vibrating conveyor that gently carries them to the milling area. In the mill, skin is removed by aspirators from the onion pieces. The onions are then milled into sliced, large chopped, chopped, ground, granulated and powdered onions.