In the past thirty years, the market for cut flowers has become a global one; flowers and cut foliage sourced from throughout the world are sold as bunches or combined into arrangements and bouquets in major target markets such as North America, Japan and the EU. The high export value of cut flowers has led to dramatic increases in production in many developing countries.
Production of cut flowers and foliage can be highly profitable in countries with an ideal growing environment (particularly those close to the equator), and low labour costs. The costs of establishing production in the field or even in greenhouses are relatively modest, and harvest may start within a few months of planting.
Because of this global production system and marketplace, as well as the high perish-ability of cut flowers, air transport has been the transport system of choice. Although air transport is rapid compared to surface modes (truck, sea container, etc.), the nature of cut flowers and foliage leads to their rapid deterioration even during the relatively few hours that they are in transit when transported by air. It has frequently been demonstrated that transport of flowers in surface modes that permit maintenance of the cold chain results in better turn-outs than air freight with uncontrolled temperature environments.
By far the most important part of maintaining the quality of harvested flowers, is ensuring that they are cooled as soon as possible after harvest and that optimum temperatures are maintained during distribution. Most flowers should be held at 0 – 2°C. Chilling sensitive flowers (anthurium, bird of paradise, ginger, tropical orchids) should be held at temperatures above 10°C.
Individually, the temperature of flowers fluctuate rapidly, changes in temperature can occur within a few minutes of picking. Therefore, while individual flowers can be cooled quickly, it is also true that individual flowers brought out of cool storage into a warmer packing area will overheat quickly and develop condensation prior to packing. The simplest method of ensuring that packed flowers are adequately cooled and dry, is therefore to pack them in the cool room. Although this method is not always popular with packers – it will probably increase labour cost and may slow down packing somewhat – it ensures a cooled and dry end-product.
Once packed, cut flowers are difficult to cool. Their high rate of respiration and the high temperatures of most greenhouses and packing areas result in heat build-up in packed flower containers, unless measures are taken to ensure temperature reduction. It is therefore necessary to cool the flowers as soon as possible after packing. Forced air-cooling of boxes with end-holes or closable flaps is the most common and effective method for pre-cooling cut flowers. In forced air-cooling, refrigerated air is sucked or blown through a packed box of flowers to reduce their temperature quickly. Most flowers can be cooled to recommended temperatures within 45 minutes to an hour, and some cut flowers can be cooled in as few as 8 minutes. For small volumes of packed flowers this is done by stacking boxes around a fan inside an existing cooler.
In larger systems many fans are permanently mounted against a wall, and pallets or cartloads of flower boxes are positioned next to the fans. The refrigeration system needs to be carefully designed and sized for forced air-cooling.
Cooling time calculations
The time necessary to reach a desired temperature is expressed in terms of a typical cooling curve.
Note: Cooling curve for cut flowers in a forced air cooler with supply air at 32 F / 0 ° C. The half-cooling time for these flowers is 10 minutes.