1. Cools produce rapidly (about 15 times faster than air).
2. Allows for greater harvesting and marketing flexibility.
3. Easily handles large amounts of produce.
Most fresh fruits and vegetables require thorough cooling immediately after harvest in order to deliver the highest quality product to the consumer. Proper cooling delays the inevitable quality decline of produce and lengthens its shelf life. Most wholesale buyers now require that fresh produce items be properly and thoroughly cooled before they are shipped to market.
When warm produce is cooled directly by chilled water, the process is known as hydrocooling. Hydrocooling is an especially fast and effective way to cool produce. With modern technology, hydrocooling has now become a convenient and attractive method of post-harvest cooling on a large scale.
Many types of produce respond well to hydrocooling. Produce items that have a large volume in relationship to their surface area (such as apples, cherries, and peaches) and that are difficult to cool can be quickly and effectively hydrocooled. Unlike air cooling, no water is removed from the produce. In fact, slightly wilted produce may sometimes be revived by hydrocooling.
Types of hydrocoolers
There are several different hydrocooler designs. Hydrocooling methods differ in their cooling rates and overall process efficiencies. In addition, hydrocoolers vary in the method of cooling that is used and the method of moving or placing the produce so that water comes in contact with it. Four types of hydrocoolers that are commonly used are discussed below: conventional, batch, immersion, and truck hydrocoolers. Conventional Hydrocooler A conventional hydrocooler allows the produce, either in bulk bins or in cartons, to pass along a conveyor under a shower of chilled water. Warm produce is placed on one end of the conveyor, and cooled produce is removed at the opposite end. The rate at which the conveyor, and thus the produce, is advanced through the shower is about 1 foot per minute and may be varied on most hydrocoolers to suit conditions.
Hydro-cooling for cherries
Batch hydrocoolers are enclosures that do not have conveyors. Palletized cartons or bulk bins of produce are loaded into the enclosure with a fork lift. The door of the enclosure is then closed, and large quantities of chilled water are flooded over the top of the produce, collected at the bottom, re-cooled, and recycled. Most batch hydrocoolers can cool only one pallet of produce at a time, as shown in Figure 2. However, some larger batch units are occasionally built that can cool as many as eight pallets at once. These hydrocoolers generally have a smaller capacity than conventional hydrocoolers and therefore may be less expensive. They are better suited to growers with a limited amount of produce that could not economically justify a larger unit.
Immersion hydrocoolers are large, shallow, rectangular tanks that hold moving chilled water. Crates or boxes of warm produce are loaded into one end of the tank and moved by a submerged conveyor to the other end where they are removed. Crushed ice or a vapor-compression refrigeration system keeps the water cold, and a pump keeps the water in motion. Most produce is only slightly buoyant so it tends to stay submerged. The length of time the produce remains in the water varies with the initial conditions and desired ending temperature.
Immersion hydrocooling is nearly twice as rapid as conventional hydrocooling methods. With conventional hydrocooling, the cold water that is sprayed or flooded over the produce contacts only a portion of its surface. The result is less than maximum heat transfer. Immersion hydrocooling reduces the temperature more rapidly because moving chilled water completely surrounds the exterior surface.