Transport practices for lettuce
Transport of fresh products like lettuce generally takes place in (refrigerated) trucks, reefer containers, or by plane. Checks and proper loading are always important to maintain good (temperature) conditions for the product during transport. For fresh products, refrigerated transport is often necessary. Trucks and reefers can maintain a low temperature, but do not have enough cooling capacity to lower the product temperature. Therefore, products must be pre-cooled before entering the refrigerated truck or reefer. Careful driving and handling are essential to prevent damage to produce from mechanical actions.
Optimal transport conditions
Loading and transport of lettuce from the field or the greenhouse to the packhouse should immediately follow harvest; it is essential that lettuce is cooled as soon as possible. Pre-cooling of the lettuce, usually to a temperature around 0.5 °C, is absolutely necessary before the product enters the refrigerated truck or reefer for further transport. Controlled Atmosphere (CA) has only a limited benefit for lettuce quality. However, for long (overseas) transport duration CA can be applied. Fresh-cut is often already packaged under Modified Atmosphere (MA) with low O2 and high CO2 and should not be combined with CA. Mixed loads with ethylene producing products must be avoided.
Attention points during loading and transport of lettuce
Loading of crates at the field. Photo by BearFotos/Shutterstock.com
Loading at the field or greenhouseThe lettuce should never be exposed to direct sun during loading and transport. Upon pick-up, the crates or other packaging must be carefully stacked and tightened to ensure they do not shift or fall over during transport. In the case of larger trucks and loads that do not fully occupy the truck floor, the tightening must be done by placing (pallet-)edge protectors at the edges of a batch of stacked field crates. Especially for warm loads (picked up at harvest), air ventilation through the stacks should be guaranteed.
Loading for further distribution. Photo by StockphotoVideo/Shutterstock.com
Loading after pre-coolingThe loading must be realized preferably from a climate-controlled loading dock via “cold tunnels” into the truck (or reefer). These “cold tunnels” prevent ambient air from entering the pre-cooled truck or the climate-controlled loading dock. Apart from maintaining the lettuce at the desired low temperature, this is important in order to avoid condensation, which will occur when warm moisture-laden air comes in contact with the colder produce or packaging. Stack with care for a stable load and to allow a good air flow.
A temperature logger. Photo by WUR
Temperature loggingThe cold chain should not be broken, the lettuce remains best in the set temperature range. Lower or higher temperatures can easily lead to loss of quality. Product and/or its packaging that are re-warmed when the cold chain is broken, can have condensation. Good quality control during transport includes temperature logging. Temperature loggers are retrieved at unloading and the data is processed.
It is recommended to do a quality check during unloading. Photo AnEduard/Shutterstock.com
UnloadingUnload the cargo carefully to avoid handling damage. The pallets with lettuce must be moved directly to a cold storage room. It is recommended to sample produce for inspection at this moment. Visual appearance of lettuces, but also of packaging and pallets can be documented via photographs. A quality inspection report is made when produce is imported from overseas. Based on this report the load will be accepted, rejected, or accepted under conditions.