Harvest frequency can have a major influence on strawberry fruit
quality. Strawberry fruit ripen rapidly on the plant. Fruit color develops quickly going
from first blush to fully red in only 24 to 36 hours. While the fruit is turning red other
changes occurring include: increase in sugar content, loss of acidity, development of
flavour compounds, and rapid softening.
A strawberry that is 50% red will lose 25% of its firmness in
the 24 hours it takes to turn fully red and an additional 15% if it remains on the plant
another 24 hours. When the strawberry is removed from the plant color and flavour
development continue, but there is little change in firmness or sugar and acid content.
The rapid changes occurring in ripening strawberries makes the timing of harvest a
critical factor determining fruit quality. When the fruit has just reached full color it
has developed acceptable flavour and appearance without becoming excessively soft. To
harvest fruit at this peak maturity, fruit must be harvested daily and all ripe fruit must
be removed. Any fully red fruit left on the plant will become soft and overripe and lower
the quality of subsequent harvests. Uniform maturity obtained by daily harvests will give
a high quality product with improved shelf life.
Postharvest cooling is essential to extend the market life of
strawberries. Harvested fruit should be removed frequently from the field and cooled
within 2 hours of harvest. Prior to cooling harvested fruit should be shaded to avoid
heating from solar exposure.
Placing fruit in a cold room is not adequate to remove field heat. Cold air must be
actively forced through the flats containing the fruit. If adequate refrigeration is
available in a cold room, this can be economically accomplished by mounting a fan on an
air plenum that can be constructed from plywood. Palletized fruit are placed against the
opening in the plenum and the fan draws cold air from the room through the fruit. The fan
should be positioned below the refrigeration unit so air warmed by the fruit will be
cooled before mixing with the room air. Forced-air cooling will cool fruit to 1░ C in 1
to 2 hours. After fruit is cooled, it should be held at 0░ C throughout transportation
and storage. Good refrigeration will reduce decay, maintain fruit shine, and prevent fruit
from becoming dark and overripe.
After cooling, if cold fruit contacts warm humid air a
temporary loss of shine will occur due to condensation on the fruit. As the fruit warms
the condensation will dissipate and the shine will return. To prevent condensation plastic
can be placed over the fruit to avoid it contacting humid air.