Agriculture Reference
In-Depth Information
storage so that skinned or deteriorated bulbs can be
removed before the saleable ones are sacked up ready
for market. Usually they are packed in labelled mesh
bags and stacked on pallets for transport to the whole-
saler or retailer.
lost. As with stage 3 of onion storage, the temperature of
the bulk shallots is then gradually lowered by adding
more cool and dry external air until a low temperature is
reached. If no refrigeration is possible, it is important to
limit ventilation to times when the outside air temperature
is more than 2°C and the air is reasonably dry (<90% RH).
It is advisable to avoid too rapid changes in temperature,
long periods without ventilation, or to allow air to enter
that is much warmer than the bulb temperature, because of
the risks of condensation.
If refrigerated storage is to be used, it is advisable to dry
the bulbs rapidly and place the bulbs into the cold store as
soon as possible after harvest, and in any case within ten
days of lifting. The temperature is first brought down by
ventilation with cool outside air, then further by adding
refrigeration, until the bulbs reach a temperature of 0°C or
better still, −2°C, provided that the temperature controls
are very precise and also reliable. At this temperature, the
air RH should be maintained at 70% and the air should be
changed at least once per day. Such a regime should allow
shallots to be kept from autumn to May with losses of
around 8% (rather than of 70-75% as would be expected
from using ordinary ambient storage).
With forced ventilation but no refrigeration, shallots can
be kept until only February-March without sprouting. After
storage, the shallot bulbs are if necessary separated,
trimmed and graded before being packed for sale (Messiaen
et al
. 1993).
Recent research on shallot storage include an
Ethiopian study, which concluded that sacks were infe-
rior to both mesh bags and boxes as containers for stored
shallots (Jemal 2000), and a Polish study on the changes
in flavonols during growth and storage (Horbowicz &
Kotlinska 2001): they reported that quercetin content
increased during the late maturation period in the field
and continued to rise during the first two months in stor-
age, after which it remained stable for a time and then
decreased slightly. The shallots in the trial were four
Polish landraces and the first four months of storage
were at about 4°C. Quecetin is of interest as an anti-
oxidant and contributes to the 'nutraceutical' aspect of
edible alliums.
Shallot harvesting, curing and storage
Specific information about this aspect of shallot culture is
not easy to find, as the crop attracts less research attention
than onions. Messiaen and his colleagues consulted
researchers and growers in France to collect the following
information, which is taken from their 1993 topic (Messiaen
et al
. 1993).
Shallots for storage are lifted by hand when the foliage
is fallen and two-thirds yellowed, and are usually field-
cured on top of the beds for five to eight days before being
taken to the storage site. Sometimes grading is done and if
leaves and roots are removed at this stage, good ventila-
tion in storage is more easily achieved. On a small scale,
the bulbs are simply placed on trays or in crates in a natu-
rally well-ventilated shed or barn. Forced ventilation
methods are also used, sometimes with temperature con-
trol. The following data are quoted: one cubic metre of
storage holds about 450 kg of bulbs, an airflow rate of
240 m
3
per hour and per m
3
of storage (500 m
3
/h.t of bulbs
and a static pressure equivalent to 30 mm of water column
are needed for a layer of bulbs 2 m thick), the air distribu-
tion channels should be of the correct dimensions, heating
should be capable of being adjusted appropriately and the
regulation of heating should be precise and reliable.
Various types of systems can be used: shallow trays or
shelves with all-round air circulation, bulk storage with
under-floor air channels, or bin storage in which the air is
forced up through each bin by selective blockage of exit
channels at the base. All of these methods are similar to
those used for onions. Also as in onions, a drying phase
starts the controlled drying process, in which the tempera-
ture is gradually raised to 35°C and the RH is allowed to
adjust to 70% by an increase in the amount of air recircu-
lated within the store from 50% to 90% over time. This
phase is considered complete when the difference in tem-
perature between air entering and leaving the store is not
more than 1°C to 1.5°C. Then follows a phase of con-
trolled heating or 'thermotherapy' to use the French term,
the aim of which is to deter the spread of neck rot.
However, as Messiaen
et al
. (1993) point out, this phase
may actually favour the activity of the basal rot organism,
Fusarium oxysporum
f. sp.
cepae
, if this fungus is pre-
sent. The mass of the bulbs is kept at 35-36°C for four
days, and the RH at >70% so that not too many skins are
GARLIC HARVESTING, CURING
AND STORAGE
Garlic is also often hand harvested and allowed to dry out
on beds in the field. Messiaen
et al
. (1993) in France rec-
ommended harvesting the bulbs before they are perfectly
mature, in order to avoid contamination with the fungus
Helminthosporium allii
: they suggested that the bulbs
