Tímarit Verkfræðingafélags Íslands - 01.12.1967, Blaðsíða 97

TlMARIT VFl 1967
95
Achievements of the Freeze-Drying Industry
By. dr. Ettrup Petersen
A/S Atlas
Introduction
I feel much honoured by your kind invitation
to come here today and make a statement about
the development of the freeze-drying industry,
and I thank you most heartily for having given
me this opportunity.
Taking into consideration that large scale
freeze-drying of food materials was initiated only
6—7 years ago, the first and most imminent
question to be answered is whether the freeze-
drying process has justified itself in practice.
The answer is a very clear yes. Today a total
of abt. 70 factories are in operation or about
to he started all over the world, and production
figures from USA show the following develop-
ment in the quantities of prepared raw material
treated per year:
1962 3.000 metric tons
1963 6.000 —
1964 12.000 —
1965 est. 20.000 — —
A young industry, which can double its
potential every year, can most certainly be
considered to be a lively baby holding promises
for the future.
I do not intend today to go deeply into the
theory of freeze-drying, but for those who are
not acquainted with this process, I will give a
very short explanation.
The boiling point of water is lowered when
the pressure on the surface is lowered. At 4,6
mm absolute Hg pressure (also called 4,6 Torr)
water boils at 0°C. If the pressure is lowered
further the water freezes to ice, and if we trans-
fer heat energy to the ice under these condi-
tions, it will not melt, but will evaporate directly.
So in order to freeze-dry a foodstuff, it is
frozen first and then it is transferred to a vacuum
cabinet in which pressure below 1 Torr can be
attained. When transferring heat from heated
surfaces the ice will evaporate directly without
melting and as the vapours cannot transfer
water soluble components inside the material,
there will be no physical changes in this, apart
from the removal of water. In conventional dry-
ing at pressures above 4,6 Torr liquid water
will travel to the surface, leaving the water
soluble components as a scale which will impair
further drying and rehydration.
Advantages of freeze-drying
The main advantage of freeze-drying is that
it produces foods of higher quality than any
other drying method. This is due to the very low
temperature at which the process is performed,
and it applies to such important qualities as
appearance, flavour, rehydration, texture and
tenderness.
Freeze-dried products also compare well to
frozen and canned foods. For vegetables there
is hardly any detectable difference and for fruits
the advantage will be on the side of the freeze
dried products. Meat and seafoods could be
found somewhat inferior to the frozen or canned
counterparts, but when prepared in dishes with
the proper sauces, these are absolutely acceptable.
Freeze-dried coffee is definitely superior to
spray-dried and tea can only be dried into an
acceptable powder by freeze-drying.
A definite advantage of freeze-dried products
is that their weight is only 10-30% of the
original material. This makes distribution very
easy and even air-transportation could be a
commercial possibility.
The storage life of freeze-dried products
when properly packed is several years, and they
are therefore superior to frozen foods in this
respect and well comparable to canned goods.
It should just be mentioned that freeze-dried
foods can be stored in ordinary warehouses and
transported, sold and kept in the kitchen without.
refrigeration.