380 Handbook of herbs and spices
the same compounds as those active in fresh garlic and onions, they contain them in
smaller amounts. For this reason, larger amounts of leeks may need to be eaten to
obtain the benefits provided by its Allium family cousins. Fortunately, the mild, sweet
taste of leeks makes this easy (Anon., 2005a).
Stabilize blood sugar levels
In addition to their unique properties as Allium family vegetables, leeks also emerged
from a food ranking system as a very good source of manganese and a good source
of vitamin B6, vitamin C, folate, and iron. This particular combination of nutrients
would make leeks particularly helpful in stabilizing blood sugar, since they not only
slow the absorption of sugars from the intestinal tract, but help ensure that they are
properly metabolized in the body (Anon., 2005a).
22.6 Quality issues..................................................................................
Leeks of good quality have fresh green tops and well-blanched stems or shanks. In
order to attain 15–20 cm or more of white shank, a common practice is to plant the
young transplants in a shallow trench 10–15 cm deep and as the plants grow the rows
are cultivated and gradually hilled to promote more white stalk development. The
greater the length of white shank, usually the more premium is the product. Wilting
and yellowing of the top will downgrade the quality. Bruised tops are unimportant if
they can be trimmed without spoiling the appearance. Crooked stems and bulbous
bases are not desirable characteristics and should be avoided in order to maintain a
premium pack (Randy Baker, 1991).
Leeks must be grown to a certain size before they are marketable. The criteria of
marketability vary from outlet to outlet, and various specifications for marketable
size have been used in scientific studies on the crop. Currently, leek of pseudostem
diameter greater than 20 mm and length greater than 150 mm, including a 50 mm
‘flag’ of green leaf at the top, meet UK supermarket specifications. Such leeks should
have an average fresh weight of about 160 g. In some past studies, all leeks of
diameter greater than 12.5 mm have been classed as marketable, and in some more
traditional markets large leeks, greater than 40 mm diameter, are required. In fact, the
leek is a variable crop and some grading into different sizes is essential to satisfy the
requirements for uniformity demanded by most outlets.
22.6.1 Post-harvest handling
Following lifting, the outer leaves are removed, the remaining leaves are shortened and
the plants are washed or brushed, graded for length and diameter and packed into boxes.
Leeks are sometimes sold loose and sometimes pre-packed in trays with plastic covers
or in plastic bags. The requirements for pre-packing leeks include uniform lengths of
the white portion of the pseudostem. New products, such as ‘baby leeks’, are also
appearing in European markets. In Europe about 90% of the leek crop is sold on the
fresh market and 10% is processed by the industry. Some processed leeks are used for
freezing, some are freeze-dried and some are used to prepare ready-cooked dishes.
Decoteau (2000) reported that harvested leeks are cooled by hydrocooling, icing,
or vacuum cooling to preserve freshness. If vacuum cooling is used, the leeks are
often wrapped in ventilated polyethylene to prevent desiccation. Leeks held at near
6 ∞C and about 90% relative humidity can be stored for two to three months.