Agriculture Reference
In-Depth Information
Recently, industrial techniques for extracting the aromatic flavour
constituents from unheated homogenates of bulbs have been developed. The
oil-soluble aromatics are extracted into food-grade solvents, and this can then
be evaporated to concentrate the flavour substances and recover the solvent.
Because these aromatic oils are so concentrated, they are sometimes dispersed
into a solid phase using salt, dextrose or flours as a carrier. Alternatively, they
can be micro-encapsulated using edible polymers, e.g. gum arabic. These forms
of dilution and dispersal simplify the mixing and incorporation of the flavour
oils into manufactured foods.
Dehydrated products
Onions and garlic are widely used in dehydrated form. Onion varieties for
dehydration should be white-fleshed and should have a high dry matter
percentage. Suitable varieties include the well-known cvs 'Southport White
Globe' and 'White Creole', bulbs of which contain 17-21% dry matter. The
processing involves first washing the bulbs, removing the skin, roots and tops,
surface sterilization by flame or alkali, washing and then slicing or chopping.
The slices are dried in hot air, starting at 75°C and decreasing to 60°C in three
stages as the moisture content decreases. Drying at too high a temperature
causes darkening (caramelization). Hot-air drying is followed by a final drying
to 4% moisture while the flakes are agitated in a blast of warm air. The
production of dried garlic is very similar, except that a maximum drying
temperature no higher than 60°C is necessary. Dried flakes may be further
processed into powders.
Onion and garlic powder and flakes are widely used in manufactured
soups, ketchups, sauces and mayonnaises. For use in catering, onion or garlic
powder may be blended with 70-80% salt plus 1-2% calcium stearate to
produce onion or garlic 'salt'. The dehydrated products may be incorporated in
more elaborate pre-prepared foods. For example, onion 'rings' suitable for deep
frying or selling cooked and packed as a snack food are produced by extruding
a paste containing dried onion. Dehydrated green onions, leeks and chives are
also produced. The best-quality dehydrated chives are produced by freeze-
drying the chopped leaves under reduced atmospheric pressure, followed by
packing in nitrogen-flushed polyethylene bags (Poulsen, 1990).
Pickles
In many countries pickled allium bulbs are eaten in large amounts. Onions for
pickling are either common, yellow-brown-skinned varieties or special white
'silverskin' types. Small bulbs, suitable for pickling, are produced by growing at
a high plant density (see Figs 6.7 and 6.8). Onions for pickling are first peeled,
