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Fish Preservation and Processing
| By goGreen | June 29, 2012 |  |
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 consistently 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:
- Cooling and icing
- Salting and pickling
- Pastes and sauces
- Canning and bottling
- Air drying and smoking
- 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.
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, specially 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 ice makers 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.
Topics: Agri-Business, Food Processing, How to, Miscellaneous | No Comments »
