Tímarit Verkfræðingafélags Íslands - 01.12.1967, Síða 99

TlMAR.IT VFl 1967
97
apply his fantasy to the food habits of the
country in which he is working.
Retail sale
By far the most interesting item for retail
sale is freeze-dried instant coffee powder. This
is due to the fact that this coffee has more
aroma than spray-dried coffee and can be pro-
duced as a porous granulate which dissolves more
readily than spray-dried powder. Freeze-dried
coffee is on the market in Europe and USA
and several new factories will start production
in the near future.
Market testing has proved that an appreciable
number of buyers are prepared to pay up to
30% more for freeze-dried than for spray-dried
coffee, and this amply compensates the higher
production costs for the former.
The retail market also absorbs such items as
freeze-dried instant cream, cottage cheese etc.
Military purposes
Even if freeze-dried products seem to suit a
number of military purposes ideally, it should
be realized that this market is to-day of minor
importance in proportion to the civilian market.
In Europe less than 10% of the total production
is absorbed by the military and in USA the
percentage may be 12-14.
However, a steady even if minor consumption,
by the armed forces could always be counted on.
Foods for camping
Is was originally thought that freeze-dried
foods could command a big market for campers,
mountaineers, expeditions etc. However, practice
seems to have proved that this purpose does not
seem to promise any sizeable volume.
Institutions
Institutions like hotels, hospitals etc. consume
highly specialized items hke shrimps and mush-
rooms. Due to the hard bargaining on price, this
market is a most difficult one to penetrate and
no great hopes should therefore be attached to it.
Developments in machinery for freeze-drying
Having now considered the enormous amount
of energy and development work which has been
apphed to the product side of freeze-drying, it
will also be justified to give some consideration
to the development of the plants and machinery
for this industry.
The basic fact here is that whereas the
industry started off with machines in which the
heat transfer from the heating plates to the
drying goods was based on contact, to-day heat
transfer by radiation is the prevailing method.
This is not due to the fact that radiation dry-
ing is faster than contact drying, as certain
materials could still be dried in proportionate by
less time by contact. The main reason is that
the internal handhng and transport through the
plant could be mechanized to a higher extent in
a radiation plant as a radiation plant is cheaper
to build than a contact plant. As an example of
an up-to-date plant, I shall now describe the
ATLAS Ray-75 plant.
The raw material is sorted, cleaned and cut to
the desired size. Thereafter it is placed on anod-
ized aluminium trays, normally with loads of 10-
14 kg per square meter. The trays are in turn
kg per square meter. The trays are in turn
placed on the frames of a trolley which is
suspended on a monorail, so that it can be
pushed through the factory with a minimum
of effort.
The loaded trolley first enters a freezing tunnel
in which the material is frozen at a temperature
suitable for giving optimum of drying time and
quality. After freezing the trolley can either go
direct to the drying cabinets or be diverted
into a coldstore for later use. The loaded tray
area is totally 70 m2 per cabinet meaning that
800-900 kg of material could be treated [per
batch]. There are 16 tiers of radiant heating
plates in each side of the cabinet, and the
distance between the plates is 3”.
In the middle of the cabinet there is a passage
of 400 mm, allowing the supporting structure of
the trolley to pass and also giving passage for
inspection and cleaning.
The cabinet is designed as a horizontal
cylindrical vessel with a diameter of 2200 mm
and a cylindrical length of 4000 mm. At either
end a door is situated, allowing loading of the
wet product in one end and discharge of the dry
products at the other end. The heating plates are
covered by a special radiation enamel and all
other internal surfaces are coated with a sani-
tary enamel.
The trolley enters the cabinet in such a way
that the loaded trays are suspended safely be-
tween the heating plates without touching these.
This is important as hereby pure radiation drying
can be performed.
The heating medium passing through the