Contact Us

James Theuri
Extension Educator, Local Food Systems and Small Farms
University of Illinois Extension
1650 Commerce Drive
Bourbonnais, IL 60914
Phone: 815-933-8337
FAX: 815-933-8532
jtheu50@illinois.edu

Laurie George
Extension Educator, Local Food Systems and Small Farms
University of Illinois Extension
4618 Broadway
Mt. Vernon, IL 62864
Phone: 618-242-0780
FAX: 618-242-0781
ljgeorge@illinois.edu

Food Safety

Food Safety

General

GAPs - Cooling Produce after Harvest

James Theuri (815-933-8337; jtheu50@illinois.edu)

In order to remain competitive, growers must ensure that the quality of produce is maintained as well as possible from harvest to time of consumption.  Harvest should be done at the right temperature to avoid late-day field heat, and cooling should be done as soon as possible to remove field heat.  Proper cooling inhibits/slows enzymatic degradation and respiratory activity (softening), slows water loss (wilting), hinders growth of decay-causing organisms (fungi and bacteria), and reduces production of ethylene (ripening hormone). In addition, cooled produce can be sold at a later date, increasing marketing flexibility.

Requirements for cooling differ with different commodities, product packaging type (box, bin, or bag), product flow capacity (rate of cooling of each method), and economic considerations (profit margins, cost-benefit ratio, etc.). Produce should ideally be harvested during the coolest part of the day and kept in the shade away from direct sun. Common methods of cooling include

* Room cooling in an insulated room equipped with refrigeration units.

* Forced air cooling with fans to force cool air inside the unit; it is usually 75 to 90% faster than room cooling.

* Hydrocooling uses running water over water-insensitive food commodities, thus absorbing heat off the produce. However, hydrocooling is only about half as efficient as forced cooling.

* Top or liquid icing: crushed ice is added to container over top of the produce by hand or          machine, as in dense packages of sweet corn or broccoli that cannot be cooled with forced air.

* Evaporative cooling uses misting or wetting the produce in the presence of a  stream of dry air. This method works best when RH is less than 65%, and at best only reduces produce temperature by 10 to 15o F.

How important is cooling for produce quality? Studies show that for each hour of delay between harvest and cooling, one day of total shelf life can be lost.  It is particularly rapid for strawberries: a 4-hour delay causes unmarketability of 40% of the crop, while an 8-hour delay results in 60% loss of harvested crop.

Wash water temperature is important not just to keep produce cool, but to also slow the rapid loss of a disinfectant such as chlorine from the water. Chlorine can also become unavailable if it is adsorbed by organic matter, or if the water becomes too acidic. For best sanitation, chlorine should be monitored continuously, for example using test strips that are dipped in the water and the change in color of the strip is checked against a color code whose intensity correlates with the amount of chlorine in the wash water.

For additional information, see http://jhawkins54.typepad.com/files/konieczka---harvests-and-handling-1.pdf, http://jhawkins54.typepad.com/files/konieczka---post-harvest-standards-and-safety-1.pdf, and http://jhawkins54.typepad.com/files/kindhart---cold-storage-conditions-and-how-to-achieve-them-1.pdf from the 2013 Illinois Specialty Crops, Agritourism, and Organic Conference (ant the slides in each presentation that provide useful references).