Quite a variety of organic product on the order guide isn’t it? What may be one stop shopping for you is a bit different from the purchasing side when bringing it to our warehouse (distribution point.) Let’s start with vegetables. Yes we know it grows in the field but how does it get into that box to you? When the commodity has reached it’s point of maturity for harvest, it takes a crew that starts very early in the morning (if working in the afternoon when it is warm tends to decrease the life of the product) to size up the veg, cut it and bunch it into 12ct or 24ct (or naked 12ct or 24ct heads). Wait, it’s a cauliflower field. We have to size up uniform heads of 9ct, 12ct or 16ct. Or is it broccoli..why then we make it 14ct (bunched) or loose broccoli crowns. There are others (celery can be 24ct, 30ct, 36ct and even 48ct which is very small size) but safe to say when you read thru the guide you will see it marked as count most of the time, but we even have some product lines listed per weight (bag 10lb or 25lb, other specialty product as 5lb/10lb. The main area to remember when in the field is what makes the best bunch size/count that will fit best in the box to safely get it towards it’s final destination. That will be another blog but let’s go thru post harvest of veg from the field before it is shipped out to our warehouse for distribution.
Lettuce harvested in the field
Now that Mr. Box has been harvested from the field, it is very critical to get it to the growers warehouse as soon as possible to get it cooled/iced to maintain its freshness. It may take 1-2 hours but that is important as the “life” of the product starts to lessen for each hour past that sweet spot of timing from field to the cooler. Once it gets to the cooler it is then put in one of the different possible processes (depending on the product): vacuum tube, hydra cooling, or icing machine. Once in from the field it is necessary for the heat to get removed from the product since the longer this heat remains, the breakdown process starts to work faster diminishing the life of the product. Let’s start with the vacuum tube process which is mostly used for all lettuces, greens & other row crops. The information below is from Southern Vacuum Cooling (one of the many companies that specialize in vacuum tubes, icing operations.)
What is the process of vacuum cooling?
The process of vacuum cooling is the rapid refrigeration of a porous product through moisture removal. Once a product is cut, heat and moisture begin to take their toll. The product will begin to rot from the inside out. When placed in a cold room, the heat is removed in a slow continuous process. However with vacuum cooling the heat is removed very rapidly, allowing for earlier shipping and a fresher product.
After the product is harvested and packaged, it is placed on pallets for shipping. The pallets are loaded into a vacuum tight chamber and the process begins. The equipment drops the pressure inside the vessel by removing air through vacuum pumps. Once the level of vacuum reaches the "flash point" moisture and heat are removed from the product in the form of water vapor. The lower the pressure inside the chamber, the lower the boiling point of water. As the vacuum goes deeper, more water vapor is removed and the product temperature is reduced until the desired temperature is achieved.
The water vapor must be removed in order for the process to work efficiently. The vacuum draws the water vapor past refrigeration coils which condenses the vapor back into water. These two systems allow the process to achieve desired product temperature more rapidly than any other post harvest cooling technique.
The rate at which a product can be refrigerated is directly related to the surface area, density of its tissue and the amount of temperature drop. Typical cooling times range from 20 to 40 minutes at a temperature drop from 80 to 36 degrees Fahrenheit. The average moisture loss is one-percent for each eleven-degree Fahrenheit temperature drop.
A hydro-vac system can help reduce moisture loss. This works by spraying clean water over the produce during the vacuum cooling cycle. More info on that process is below these pictures.
Lettuce cartons from the field going into a vacuum tube.
Cauliflower from the field going into a vacuum tube.
Hydrocoolers are another process used for getting the heat out of produce from the field before putting it in the warehouse coolers for shipping. (From the North Carolina State Extension Services) a 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. An example of a hydrocooler is shown below.
A frequent complaint about a conventional hydrocooler (let’s remind ourselves the term “conventional” does not mean non-organic, more of a category tem for these type of coolers) is that they do not cool all containers uniformly. The chilled water may not be evenly distributed throughout the load, resulting in undercooling of some parts. To overcome this deficiency, some batch hydrocoolers use a high-capacity fan to pull a fine mist of chilled water through the produce packages. The forced air has the effect of making the cooling more consistent because it pulls the water past the produce more evenly than would occur by gravity flow alone. This design, known as "hydro-air-cooling," has been successfully used with items that are particularly difficult to cool.
Image of the hydrocooling of produce.
Icing Process (Thanks again to the North Carolina State Extension Services)
Sometimes known as slush icing, liquid icing is the preferred method when large amounts of produce must be iced in a relatively short period of time. The required equipment consists of an ice crusher, a slurry tank with mixer, a pump, and delivery hoses.
In the simplest form of liquid icing, a mixture of water and finely crushed ice is pumped into open containers traveling along a conveyor under an injection nozzle, as shown below. This method is a significant improvement over hand icing because the water carries the ice into the voids throughout the package, thus bringing it into greater contact with the produce.
Liquid icing may be considered a hybrid of package icing and hydrocooling. The chilled water in the slurry has a pronounced cooling effect on the produce. In the liquid icing of broccoli, it has been estimated that as much as 40 percent of the total product cooling is accomplished by the water alone. The balance of the cooling is accomplished by the ice as it melts inside the carton.
If the produce has been packed and palletized in the field, the water and ice mixture can be alternatively pumped from a hose into the hand openings of each container, as shown in the next image below. This method is fast and effective, and it does not require that the cartons be opened or removed from the pallet. With the proper equipment, two workers can liquid ice a pallet of 30 cartons in about 5 minutes.
An even faster and more automatic method for liquid icing of palleted produce has been developed, as shown in the photo below. A pallet of filled cartons is placed inside a metal enclosure that is rapidly filled with a slurry of water and ice. The water and ice penetrate all the voids in the cartons. After the enclosure is entirely filled, the excess slurry is drained away, leaving the ice inside the cartons. An automatic pallet-icing operation can be controlled by the lift truck operator alone.
Liquid icing is an excellent cooling method, although it does wet the produce. The surface of warm, wet produce provides an excellent site for postharvest diseases to develop. Therefore, it is essential that, once iced, produce not be allowed to rewarm. Getting the iced product immediately into the coolers will generally prevent any post harvest issues from developing.
Now if you are still with me on this blog regarding post harvest handling of vegetables, I commend you. I have to deal with the not so glamorous areas of getting great organic produce to our warehouse but feel it is necessary for you to see there is more to that bunch of crisp greens in your hands. Other areas for future blogs will be post harvest handling of fruits, box size and transporting the product from the growers cooler to our warehouse. Stick with me and we will get you as close to the field as possible.
Cheers! Go Organic!
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