Dear colleagues,
Since I gave some reference on the subject I feel obliged to make some
clarification. Fish icing is not made in abstract but in a container and
within a given environment. For instance, taking as example an insulated
fish container in a tropical climate, the idea is that the insulated
container keeps ice from melting and ice keeps fish from (quicker) spoilage.
In tropical and subtropical conditions more ice is utilised in practice to
keep fish at (near) 0 degree C than the needed for bring fish form water
temperature (the original fish temperature) to near 0 degree, therefore ice
losses become more important than the ice needed to chill fish.
Cost of icing as any cost is a relative figure. In developed countries it is
comparatively cheap and it does not make to much sense to look in a fine
detail (in principle). However, in developing countries (tropical and
sub-tropical) the picture could change radically because the cost of ice is
(unfortunately) very often expensive when compared with the price of fish.
It is not rare the situation, in which the kg of ice costs more than the kg
of fish, particularly with small pelagic fish.
The relatively high cost of ice is due to a number of reasons. Among them
the cost of petrol to produce it, the sometimes relatively small ice plants
(economic of scale), the overall efficiency of ice plants (very often quite
poor), the competition with other needs (for instance against cooling beers
and soft drinks).
When the price of ice is above of the price of fish (or could be a
significant part of the price of iced fish) fish losses are very often
unavoidable. Then a sensible policy to reduce fish losses is to look into
the way to reduce as much as possible the ice necessary to keep fish. FAO
has been working and continues to work in this sense in developing
countries, in particular advocating the introduction of insulated
containers.
Now it comes the next point. Yes, to estimate the theoretical amount of ice
to chill fish from a given temperature to (near) 0 degree C is easy. My
favourite rule of thumb is to divide the temperature of fish in degree C by
100; if the temperature is 30 C, you theoretically will need around 300 g of
ice for each kg of fish with that purpose.
However, to design efficient insulated containers you should resort to heath
transfer calculations, and here it is the place were the theoretical models
are important to evaluate the effectiveness of different alternatives of
insulated fish containers. Of course you can do that by trial and error, but
technological development is other thing. Is not to teach people to solve a
point problem but to teach them how to solve the general problem.
Of course the first fish to be iced in developing countries is the fish to
be exported to earn hard currency (because it fetches a higher price).
However, we have to keep insisting and looking together with them the
possibility to chill also the fish for internal consumption, and more than
one time it has been possible thanks to the wise use of heat transfer and
thermodynamic knowledge. I can tell you it is an enormous satisfaction.
As Harrison Ford says in the film "Mosquito Coast" : "Ice is civilisation".
Hector M. Lupin
Fish Utilisation and Marketing Service (FIIU)
Fish safety and quality assurance
Tel.: (39)(06)570-56459
Fax. (39)(06)570-55188
e-mail: hector.lupin@fao.org <mailto:hector.lupin@fao.org>
This archive was generated by hypermail 2b29 : Wed Jul 19 2000 - 09:41:00 PDT