Hydro cooling is not the only form of pre-cooling available for produce. Other forms include room cooling, forced air cooling, vacuum cooling, and evaporative cooling. These forms are more popular in the United States.
Room cooling is when containers of hot field produce are placed in a cold room, and cooled by air. The containers are well ventilated and stacked 6 to 12 inches away from the wall, and 18 to 24 inches apart from top to bottom. Refrigeration of produce is required 24 hours a day, seven days of week. Just as in hydro cooling, surface contact must be present for efficient cooling.
Forced air cooling is designed to force air through ventilated containers, not around them as in room cooling. Forced air cooling is practical and feasible. Ideas to consider when creating a forced air cooling room include, how continuous vents will be aligned, how containers are stacked (straight or cross stacked), and the size of vents. Forced air cooling also have various methods that can be used. These methods include forced air tunnels, serpentine cooling, and cold wall. Forced air tunnel cooling allows an exhaust fan to be placed at the end of an aisle. Two rows of aisles are covered from top to bottom and at the end to create a tunnel. The fan then pushes air through this tunnel to cool produce. Serpentine cooling is designed to cool produce bins in bulk. Bins are stacked with a fork lift against a cold wall. Then every other stack is covered with canvas. The alternating layers allow air currents to circulate through the gaps. Cold wall cooling uses a fan to cool produce. A false wall is situated inside the chamber. The wall is built with a dampening system that pulls moisture with the cold air through stacked crates.
Evaporative cooling is only effective when humidity is low. Dry air is drawn through semi wet padding through vented containers of produce. As the moisture in the air changes, so does the temperature of water. The water moves from a liquid to a vapor. Vacuum cooling is used in a cooling chamber where produce has a high surface area. Produce like lettuce and other leafy greens qualify.