Harvest of lettuce
The maturity of lettuce at harvest is critical both for ensuring the quality of whole head lettuces and for the fresh-cut salads. The maturity stage has a clear influence on the susceptibility to postharvest disorders and diseases. Head lettuces should be well formed and firm, and the lettuce weight must be above a minimum, especially for the fresh-cut processing. Looseleaf lettuce is harvested when the leaves are large enough for the intended market purpose. The packaging of the harvested lettuce can take place directly in the field (field packing) or in a nearby packhouse. In all cases, the harvested product must be transported to a cooling facility quickly after harvest.
Attention points for harvest of lettuce
Maturity stage at harvest is of high importance for postharvest quality. Photo by Pormezz/Shutterstock.com
Harvest maturityDepending on the type of lettuce and the target (whole or fresh-cut market), important maturity indicators are size, head weight, head length and width, firmness and compactness. The maturity stage is of high importance because it affects the ratio volume/weight of the product, the respiration rate (immature leaves have a higher respiration rate that will cause a shorter shelf life), and susceptibility to moisture loss and quality loss such as discoloration.
Iceberg lettuce with a good compactness. Photo by WUR
Head compactnessThe degree of head compactness is an important maturity parameter for head lettuces. Soft (immature) heads are easily damaged, while very firm (overmature) heads are more susceptible to certain physiological disorders such a pink rib. Compactness can be measured by hand pressure and is used to classify in different classes from fluffy to extra-compact. A compact head that can be compressed with slightly to moderate hand pressure is generally preferred.
An example of field packing. Photo by WUR
Harvest methodHarvest methods vary greatly depending on the type of lettuce and the intended market. It is done by hand or with a lettuce harvesting machine. After cutting, the products are usually transferred into plastic field crates and quickly transported to a nearby packhouse with refrigeration. Sorting and packaging (in corrugated boxes) can also occur directly on the field: “field packing”. It is important to remove the outer leaves, contaminated with soil and possibly moulds.
Lamb's lettuce harvested mechanically. Photo by WUR
MaterialsThe availability of good, clean and sufficient materials will facilitate harvest and product quality will benefit. Ensure that harvesting materials are sanitised before use. When knives are used, they should be sharp. Field crates or boxes should be clean, stackable, undamaged and without sharp edges. A covered shaded place is necessary to place the lettuce immediately after harvest to prevent moisture loss.