As a general rule, a minimum of 10 acres of producing blueberries is required to justify the expense of purchasing a self-propelled machine. In order to further amortize the expense of operating a harvester, growers will custom-harvest other fields or other crops such as blackberries and raspberries. Canes are bent over a portable catching frame and vibrated with short bursts in order to dislodge the ripe berries. Problems with this harvesting method include having to run the berries through an air separation unit to remove the large amount of debris that is collected. On slapper machines, dislodged fruit falls to the base of the machine where it is caught on sloped catch plates.
Berries then roll to a conveyer belt that runs towards the back end of the machine.
A cup conveyer belt moves the fruit up to the top of the machine where it is sent past an air blower to remove trash and then onto a second conveyer belt that passes past an operator for inspection prior to filling a plastic processing flat. There are a number of problems inherent in the slapper principle. Because of fruit bruising, most of the harvested fruit has to be sent to a processing outlet. Branches can be broken off or scarred, allowing entrance of disease organisms. Even with a properly adjusted slapper machine, there is still a considerable amount of over-ripe or green fruit that will have to be sorted out by graders in a processing line.