TECHNICAL PAPER #44
 
 
                              UNDERSTANDING FISH
                               PRESERVATION AND
                                  PROCESSING                               
 
 
                                     By
                            Richard T. Carruthers
 
 
                             Technical Reviewers
                              Celeste Philbrick
                               Ira J. Somerset
 
                                     VITA
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA     
                     Tel: 703/276-1800 . Fax 703/243-1865
                          Internet: pr-info@vita.org   
 
                Understanding Fish Preservation and Processing
                             ISBN: 0-86619-258-1
                  [C]1986, Volunteers in Technical Assistance       
 
 
                                   PREFACE
 
This paper is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their situations.
They are not intended to provide construction or implementation
details.  People are urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
 
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis.  Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.  VITA staff included Bill Jackson as
editor, Suzanne Brooks handling typesetting and layout, and
Margaret Crouch as project manager.
 
The author of this paper, VITA Volunteer Richard T. Carruthers,
is President of Bioproducts, Inc. in Warrenton, Oregon.   The
reviewers are also VITA volunteers.   Celeste Philbrick specializes
in fisheries management and is a development specialist with
Fishtech, Inc. in Wakefield, Rhode Island. Ira J. Somerset works
with the U.S. Food and Drug Administration in Bedford, Massachusetts.
He specializes in sanitation engineering and food inspection,
and has worked in Korea and Japan.
 
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries.   VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations.  VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
 
                UNDERSTANDING FISH PRESERVATION AND PROCESSING
 
                       by Volunteer Richard T. Carruthers
 
I.  INTRODUCTION
 
The purpose of processing and preserving fish is to get fish to
an ultimate consumer in good, usable condition.   The steps necessary
to accomplish this begin before the fishing expedition
starts, and do not end until the fish is eaten or processed into
oil, meal, or a feed.  Fish begins to spoil as soon as it is
caught, perhaps even before it is taken out of the water.  Therefore,
the key to delivering a high quality product is close
attention to small details throughout the entire process of
preparation, catching, landing, handling, storage, and transport.
Fish that becomes spoiled or putrid is obviously unusable.  Fish
that is poorly cared for may not be so obviously bad, but it
loses value because of off-flavors, mushy texture, or bad color
that discourage a potential purchaser from buying.   If customers
have bought one bad fish, they probably won't buy another.  On the
other hand, if you consisitently deliver good quality at a fair
price, people will become loyal customers.
 
Spoilage proceeds as a series of complex enzymatic bacterial and
chemical changes that begin when the fish is netted or hooked.
This process begins as soon as the fish dies.   The rate of spoilage
is accelerated in warm climates.   The fish's gut is a rich
source of enzymes that allow the living fish to digest its food.
Once the fish is dead, these enzymes begin digesting the stomach
itself.  Eventually the enzymes migrate into the fish flesh and
digest it too.  This is why the fish becomes soft and the smell of
the fish becomes more noticeable.
 
There are countless bacteria naturally present on the skin of the
fish, in the gills, and in the intestines.   Normally, these bacteria
are not harmful to a living fish.   Shortly after death,
however, they begin to multiply, and after two to four days they
ingest the flesh of even a well-iced fish as enzymatic digestion
begins to soften it.  The bacterial load carried by a fish depends
on its health, its environment, and on the way it was caught.
Healthy fish, from clean water, will keep better than fish
dragged along the bottom of a dirty pond in a trawl net.
 
Both enzymatic digestion and bacterial decomposition involve
chemical changes that cause the familiar odors of spoilage.
Oxygen also reacts chemically with oil to cause rancid odors and
taste.  The aim of fish processing and preservation is to slow
down or prevent this enzymatic, bacterial, and chemical deterioration,
and to maintain the fish flesh in a condition as near as
possible to that of fresh fish.
 
Whenever fish must be kept for several hours or longer before
being consumed, they must be treated in some way to prevent
spoiling.  These are the basic means for preserving fish:
 
    o    Cooling and icing
 
    o    Salting and pickling
 
    o    Pastes and sauces
 
    o    Canning and bottling
 
     o   Air drying and smoking
 
     o   Kiln drying
 
The basic task of every fishery is to get the catch to the
consumer in good, usable condition.   The first fish caught were
probably eaten raw, on the spot.   Communities grew up near enough
to productive fishing grounds so the fish could be consumed the
day it was caught.  The earliest preserved fish was probably
accidentally overcooked, and some observant fisherman saw that
dry cooked fish kept for a period of time without spoiling.
Traditionally, air drying, salting, and smoking (or some combination
of these three) preserved fish for the short periods required
by the fishermen.  Fish preserved in these ways is often
tough and stringy, the quantities produced are small, and success
is uncertain.  Few people will eat fish preserved this way, if
they have an alternative.  Over time, other, better methods of
preservation came into being.
 
II.  VARIATIONS AND ALTERNATIVES
 
Before fishing begins, make sure that all equipment is clean.  If
a sterilizing rinse is available, use it to clean both the tools
and the place where the fish will be processed.   Make a clean,
cool place to put the freshly caught fish.   At the least, shield
the fish from direct sun, and use wet cloths spread over the fish
for evaporative cooling, which in addition will prevent it from
drying out.
 
Fishermen sometimes tend to get careless and rushed about how
fish are handled at the catching stage.   But care taken at that
point will pay off handsomely at the market.   Insofar as possible,
handle the fish gently.  Bring them aboard carefully without
banging them against things, walking on them, or dropping them.
If you use any sort of pugh or fork, be careful to stick the fish
in some unusable part (like the head).
 
Fish waiting to be processed should not be walked on.   Batches of
fish should proceed through the handling process without being
mixed up with fish from another batch.   The fish should be washed
at once with plenty of clean water.   It isn't easy to wash fish.
The wash water should be directed away from the fish in such a
way as not to contaminate previously washed fish.   Large fish can
be handled separately, but quantities of smaller fish, expecially
flat fish, need some sort of rotating washer for a really good
job.  You are trying to reduce the bacteria load by washing away
the slime.  Tossing a bucket of water over a pile of fish is not a
substitute for a thorough washing.   Many later problems, in any of
the processes to be described, can be avoided by keeping the fish
clean and cool in the early stages.
 
Cooling and Icing
 
The first and simplest method to both preserve and process fish
is to keep it cool.  Cool fish keeps longer than uncooled fish,
although both will spoil in a matter of hours.
 
If the market is only a few hours away, and if the fish will be
sold promptly, evaporative cooling might suffice.   All that is
required is some coarse cloth--enough to completely cover the
fish--and enough water to keeps the cloth damp.   The movement of
air over the water causes it to evaporate, and thus keeps the
fish much cooler and fresher than fish directly exposed.  Wrap the
fish completely in the cloth.   Any portion that is exposed to the
air will dry and become warm enough to support the rapid growth
of bacteria.  Splash water on the wrapped fish, keeping the cloth
wet but not soaked.  How well this will work depends on too many
variables to predict, but it is a distinct improvement over
uncovered fish.
 
Most fish caught are preserved with ice at some stage in their
processing.  Trained taste panels are usually unable to distinguish
well-iced fish kept less than six or seven days from fresh
fish, and storage life can be extended somewhat if antibiotics
are added to the ice.  Ice works in two ways:  it reduces the
growth rate of bacteria by reducing the temperature of the fish;
and it also washes the bacteria and slime away as it melts.
Because of this, it is important to keep melt water drained away
from the fish.
 
Fish are usually gutted and stowed mixed with ice.   Small flat
fish are stowed without gutting.   An active fish like salmon is
gutted and the belly cavity is packed with ice as it is stowed.
Fish can be iced in bulk, in large quantities, or they can be
boxed.  Boxing produces a better quality product for several
reasons:  the bottom fish are not crushed by the weight of the
fish on top; and the melt water is better able to drain away.  In
addition, it seems to be human nature to take better care of a
small box than of a pile of fish.
 
Ice is expensive and begins to melt immediately, so the fishermen
are faced with a loss before they even begin.   The temptation to
get away with as little ice as possible must be avoided.  Within
limits, the more ice the better.   The box should be lined with ice
so the fish does not touch sides or bottom of the box.   Layer the
fish, avoiding overlaps, and ice each layer as it is boxed.  If
the catch is large enough that the boxes must be stacked, try to
channel the melt water away from the bottom boxes.   Keeping the
boxes covered with wet cloth will dramatically increase the life
of the ice.
 
There is a wide range of icemakers on the market, ranging from
small flake ice machines that produce a couple of tons a day to
huge machines that make many tons.   They all require electricity
and a certain level of technical expertise to operate.   The newer
machines are built with the small operator in mind, however, and
are practically unbreakable.   With these machines, it is possible
for small operators to make their own ice.
 
Salting and Pickling
 
Salting and pickling, along with various kinds of drying, are the
traditional methods for preserving fish.   Indeed, Egyptian tomb
paintings illustrate fish being prepared for salting and drying,
and the process must be many years older than that.
 
The bacteria that spoil fish need moisture to grow.   If the moisture
in the fish can be reduced to about 25 percent of its normal
level, bacterial activity will cease.   Some bacteria are killed at
these levels, while others simply go dormant.   The fish will keep
for several years as long as the moisture level is not allowed to
increase beyond 25 percent.  Salt replaces a portion of the water
naturally present in the fish, and so reduces the moisture content
below the point where bacterial spoilage can occur.
 
The several salting methods vary mainly in the amount of salt the
fish are allowed to take up.   "Dry salting" is used to preserve
non-fatty fish such as cod.  The split fish are completely buried
in salt, and the brine liquid that emerges is allowed to drain
away.  The fish are finally dried.  In the "pickling" process, used
for fattier fish such as herring, the fish are packed in salt in
airtight containers.  Bacterial decay is reduced or prevented when
the salt has replaced enough of the moisture in the fish to
inhibit the growth of fish spoilage bacteria.
 
A combination of coarse grained salt (like rock salt) and a fine
grained salt is used.  The coarse grains keep the fish separated
so as to drain, and the fine grains dissolve quickly into the
flesh of the the fish.  Salt may be mined from prehistoric deposits,
manufactured from partly concentrated brines, or "manufactured"
by solar evaporation of shallow ponds of salt water.   Any
of these may be available to you, as well as salt that is produced
expressly for use in salting fish.
 
Some of the flavor of the finished product depends on the kind of
salt used.  Impurities in the salt, such as magnesium or calcium,
if present at too high a level, impart a bitter taste to the
final product; these impurities also interfere with the absorption
of salt into the fish.  Some common impurities readily reabsorb
moisture from the air, so if the curing salt contains enough
of these compounds the fish will become damp again and grow
bacteria.  On the other hand, small amounts of these same impurities
give the salted fish a whiter appearance that is more attractive
to some consumers.  For all these reasons, it is important
to know what kinds of salt you are using, and what their
effects will be.
 
The fish to be salted are cleaned, and the guts and gills and
sometimes heads are removed.   Larger fish must be split so they
can be opened up and laid flat in the salt.   In general, a layer
of salt is placed in the bottom of a container and a single layer
of fish is placed on it, flesh side down.   The first layer of fish
is then covered with more salt and another layer of fish is
added.  The layers of smaller fish like herring are crisscrossed.
The process is continue until the container is full.
 
The same cautions as to cleanliness and care in handling apply.
Avoid reintroducing a bacterial load.   Use clean processing equipment
and keep the work area clean.   Keep guts and offal away from
the processed fish and dispose of it in an area removed from the
cleaning area and water supply.
 
If drying is the ultimate goal, the water that is withdrawn from
the fish by the action of the salt is allowed to run off, and the
fish are restacked at frequent intervals, rotating the fish from
the top to the bottom of the pile to equalize the cure.   The fish
can remain stacked for several months in a cool climate before
being dried, but this is not possible in termperate countries.
Fish can be air dried in Norway or Iceland, but in most areas
some sort of dryer is generally required.
 
If the fish is to be pickled, it is packed in the same way, in a
container that can be sealed.   As the fish shrink, the barrels are
consolidated, putting fish from the same day's catch together.
After about ten days, half of the replaced water is drained off,
the container is packed full again with fish from the same batch,
and the spaces between the fish are filled with the water that
was drained off earlier.  The container is then sealed and stored.
 
Salting is a simple process.   It does not require much equipment
or manpower, but the product has a limited life unless it receives
some sort of additional processing such as canning or
freezing.  Drying, which is explained in the following section, is
an alternative to freezing.
 
Air Drying and Smoking
 
Even the most heavily salted fish will begin to spoil after a few
weeks at warm temperatures.  Some additional processing is required
to preserve fish in any but the coldest climates.   Moreover,
although salt alone will protect against the growth of some
bacteria, salt-loving bacteria continue to flourish.   A combination
of salt and reduced moisture, or salt and no air, will allow
fish to be kept for several years.   Bacterial activity ceases when
the moisture content is reduced below about 25 percent.   Mold will
no longer grow at a moisture level of about 15 percent.   Fish
dried to this level will last several years if not subsequently
moistened.
 
Air drying and kiln drying reduce the moisture content of fish to
the point where bacterial action ceases.   Smoking dries the fish,
and also adds bacteriacides that are present in the smoke.  The
process varies from a mild cure that will keep several weeks if
chilled, to a hard smoke that will keep indefinitely if not
moistened.
 
Fish preserved by air drying tends to be tough and stringy.  Most
people will not eat fish preserved this way unless they must.  If
the weather is dry, fish may be air dried.   Take care to keep the
fish in shade, exposed to breeze.   Keep flies and insects away!
Air drying of fish is an uncertain undertaking.   Since it requires
a low relative humidity to achieve the necessary degree of dryness,
the fish will keep only so long as it is kept dry.   On the
other hand, it requires a minimum of equipment and no technology.
It is primarily suitable for small quantities for personal use.
With a minimum of investment solar dryers can be constructed for
the drying of fish.  Solar dryers made from plastic on a wooden
frame eliminate contamination by insects and can increase ambient
temperature to accelerate drying.   They also reduce storage of
fish when rain storms interfere with sun drying.
 
 
Kiln or tunnel drying of fish is a more complex process, and the
final product is much more palatable than natural air dried fish.
It requires careful control of many variables, such as relative
humidity, air temperature and velocity, and rate of drying.  The
product will have to be stored in some sort of cold storage
because it also will draw moisture and putrify.   In kiln drying,
the fish is hung on racks in a tunnel.   Dry inlet air is heated,
circulated through the tunnel, reheated, and recirculated.  A portion
of the moisture laden air is vented off and replaced with
outside air.  Control of the humidity inside the kiln can be
accomplished by venting off more or less of the moisture laden
air from the kiln.  Midway through the process the kiln is unloaded
and the position of the fish is reversed to equalize the
drying rate.
 
With technology that could be easily adapted to other areas,
women in the coastal regions of Ghana have built up thriving
businesses in smoked fish.  With the help of the United Nations
Food and Agriculture Organization and UNICEF the women have
designed fuel efficient smokers that allow processing of fairly
large amounts of fish at a time.   The smoked fish are packed into
large baskets and taken to markets as far as a day's drive inland.
The method the women use produces a very palatable product
that can be eaten as is, by people working in the fields all day
for example, or made into tasty soups and stews.   It can also be
made into meal to serve as a high protein weaning food or additive
to other dishes.
 
Fish Sauces and Pastes
 
In areas where a rice diet predominates, a number of fermented
fish products have been developed.   If a fairly fixed procedure is
followed, the product has a more or less consistent flavor and
texture.  In areas in which dried or salted fish is impractical
because of the high humidity and temperature, fermented sauces or
pastes may be an acceptable or preferable alternative.
 
Small, ungutted fish are mixed with salt (four to five parts salt
to six parts fish) and sealed in vats or pots.   In a process that
requires several months, the fish dissolves and ferments.  The
result is a clear "pickle" with good keeping properties that is
used as a condiment for flavoring rice dishes.   Fresh or salt
water fish can be used, as well as shrimp.   The processes vary as
widely as the kinds of fish used.   The somewhat standardized Nuocmam
has been studied extensively and is representative of most of
the Southeast Asia products.
 
Fish paste is made from cleaned fish, which is mixed with salt
(one part salt to three parts fish) and allowed to digest.  Sometimes
fermented rice, roasted grains, or bran are added.   The
manufacturing methods are complicated and vary considerably from
area to area.  As a result, the product is seldom standardized.
Tastes vary from area to area, so local knowledge is imperative.
 
Bottling and Canning
 
The bottling and canning of fish requires more precision and
expense than the aforementioned methods of preservation.  Many
nations during their lean fishing seasons import large amounts of
canned fish to supply a source of protein.   In such a case,
perhaps domestic canning is a viable option.
 
The canning or bottling of fish requires a high quality product
at the onset.  It should not be employed as a last resort for
unsold fish.  Consumption of such fish may cause severe illness.
Bottled fish is usually prepared for personal consumption.   The
bottled fish is usually cooked, boned, and put in a pickling
solution, then stored in sterilized jars with rubber sealed lids.
 
Canning, on the other hand, entails placing the fish in a tin can
with a lid, removing the air within the can through heat treatment,
sealing the lid entirely, and then heating a second time to
a specified degree.
 
The two most important considerations of this method are the
availability and expense of the cans or bottles and strict quality
control of the product.
 
Other Methods of Preservation
 
There are several other methods of preserving fish, most of them
requiring sophisticated technologies that are probably not applicable
in this context.  It is, however, worth mentioning them
briefly:  Freeze drying involves the use of a vacuum to draw water
out of the fish.  Irradiation can be used to kill the microorganisms
in the fish; however, this technology is still experimental.
Another method of preserving fish, pouch technology, is advanced
but may be usable in some locations.
 
There is a level at which the best information is available from
the manufacturer of the processing equipment; if you are interested
in these advanced preserving techniques, the job becomes
one of choosing a reputable local agent.
 
III.  DESIGNING THE SYSTEM RIGHT FOR YOU
 
The systems described range from very simple to very complex,
from cheap to costly, and so forth.   In making your decision about
which to use, study each method carefully.   Contact equipment
manufacturers, talk to specialists, read books and magazines.  Ask
for help from organizations like VITA or your local fisheries
agents.
 
Use locally available materials wherever possible.   They will
probably be less expensive and will do as good a job or better.
The trick is to achieve the desired outcome with as little outlay
as possible.  To do this you must focus on what you are trying to
accomplish, rather than the method someone might suggest.  For
instance, petrol tins would serve as "fish boxes" if they were
thoroughly cleaned and kept insulated in some way--a woven basket
would do as well or better than a plastic box.   Many naturally and
locally available materials will keep sun off fish.   Locally
available salt may make a more acceptable product than that which
you purchase.
 
Economies of scale make the cost of processing less per unit as
volume increases.  Suppose one person, who must be paid for a
day's work, can butcher 100 or 1,000 fish in a day.   It would be
better to try to maintain your volume at 1,000 fish a day than at
100.  On the other hand, 1,001 fish would exceed that one person's
capacity, and so require hiring another person.   Lowest unit
production costs occur at multiples of 1,000 fish.   Generally, you
should always consider the volume you can sell in relation to the
volume you can economically process, and try to keep the two in
balance.  Overloading your capacity always results in higher unit
costs and lost or ruined product.
 
The classic error that novice manufacturers make is to imagine
what is called a "ghost market," a market that only exists in the
mind of the manufacturer.  The manufacturer focuses on the product
and imagines that everyone will want to buy it.   They won't.  Some
successful enterprises do start big and keep getting bigger, but
most start small and grow slowly, step by step, cementing each
step as they go.
 
The most effective way to research a market is to try to sell to
it on a small scale.  Choose a neighborhood or small area that is
representative of the whole market you want to reach, and see if
the people in it will try your product.   Then see if they want
more, enough to absorb your entire production.   Suppose there are
100 people in the area you have chosen, and 20 of these are
willing to try your product.   Of the 20 who tried the product,
five indicated they wanted more.   If your whole potential market
is a city of 10,000 people, you could expect that 2,000 would try
your product and 500 would repeat their purchase.   If 500 people
will make your enterprise successful, you have created a business.
You have every right to expect that your customers will
tell their friends that you make a good, usable, consistent
product, and business will increase.   If 500 customers is not
enough to make your business a success, and if you are sure your
product is a good one, then you must decide if you can afford to
lose some money while you wait for your customers to tell their
friends.
 
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