Cooling houses' techniques keep produce fresh

Before crops reach their final destinations, they have to first make a brief stop at one of our local cooling houses.

“In order to keep the (vegetables) fresh, you have to cool and refrigerate them as soon as possible,” said John Studer, Skyview Cooling vice president.

After harvesting, crops are placed directly onto flatbed trucks and transported to a cooling house where they are prepped before being shipped to the customer.

At Skyview Cooling, 35 unionized employees work six days a week to process the millions of cartons of produce that will be dropped off in its receiving area from Nov. 1 to the end of May.

“We do three things here: We vacuum cool, we ice and we pressure cool,” Studer said, adding that the type of produce determines which cooling method is applied.

“All leaf vegetables, like head lettuce, romaine lettuce and butter lettuce, are vacuumed cooled. And vacuum cooling works by the rapid evaporation of water under very low atmospheric pressure.”

When a truckload of lettuce arrives, forklifts load the pallets into one of four vacuum tubes located near the south end of the facility.

Once inside, the atmospheric pressure is dropped, which decreases the water vapor pressure surrounding the lettuce. When the lettuce's outside pressure is lower than the lettuce's internal pressure, water begins to evaporate, which then cools the lettuce.

“Generally, it takes about 25-35 minutes to vacuum cool, depending on how much you are cooling at any one time,” Studer said.

Immediately after the lettuce is cooled, it must be placed in storage, where the temperatures are low enough to slow the lettuce's metabolic rate to maintain freshness but not too low which would cause the leaves to freeze and damage the product.

“It's very important that we work quickly. So it usually takes less than 60 minutes for a product to go from the truck to the cooling area to the storage area,” Studer said.

Some products, like broccoli, can withstand direct contact with ice. For these, Studer said, the pallets of broccoli are placed one at a time into the company's ice injector.

He said gravity is all that is used to force the ice — which is a slurry mixture of water, chlorine and salt — into the boxes. After the boxes are filled with ice, a four-inch layer is formed on top of the entire pallet, which will keep the broccoli fresh for at least a few weeks.

Studer said his two ice machines are capable of generating 170 tons of ice a day, and his average bimonthly water bill is around $3,500.

For other vegetables, like cauliflower, pressure cooling is used.

Pressure cooling involves forcing air through the stacks of boxes. The increased airflow quickly cools the cauliflower and allows it cool more uniformly.

Studer said that after a particular crop is cooled, it stays on average one or two days in storage until being shipped to its next location.

“We process around a 150 orders each day and the orders vary from truck to truck. So the product doesn't stay here for a very long time before they are shipped to the customer.”

Darren DaRonco can be reached a 539-6857 or ddaronco@yumasun.com. Follow him on twitter @YSDarrend or on Facebook at www.faceboook.com/YSDarrenD.