CULINARY INFO
Fish : Quality Points
"DISCLAIMER"
The information contained here is supplied for your interest only and further research may be required.
I have gathered it from many sources over many years. While I attempt to insure they are crossed referenced for accuracy,
I take no responsibility for mistakes - additions or corrections are welcomed.
Fish
Purchasing
When buying whole fish, it is important to be able to judge which is the freshest fish. The general appearance of the fish, especially the eyes of whole fish and the smell of the fillets are very important. Listed below are the signs to look for that will tell you how long or how well the fish has been stored:
Storage of fresh fish
The maximum shelf life of 12 days only applies, if the fish has been iced immediately it comes on board the fishing vessel and is kept on ice there after. Therefore it is important to ensure that your suppliers protect and maintain the quality of their product.
The ideal temperature for storage is 0°C, this will minimise the activity of enzymes and bacteria. Therefore chiller thermostats should be set at 0°C or -1°C, between -1°C and -5°C fish only partially freezes; this causes a disruption of cell membranes and speeds up enzyme activity and deteriation.
After 1 - 2 days on ice
Eyes : Black pupil, translucent cornea
Skin : should be covered with fresh sea slime or be smooth and moist, have a good sheen with no abrasions or bruising and no discolouration.
Gills : bright red in colour with no bacterial slime
Flesh : firm, translucent and resilient; so when you apply pressure the impression disappears quickly, the fish should not be limp.
Scales : flat, moist and plentiful
Smell : pleasant and fresh with no hint of ammonia or sourness.
3 - 4 days on ice
Eyes : pupil starting to turn grey and flatten
Skin : body slime, loss of sheen, no longer luminous
Gills : darker red in colour, start of slime build up
Flesh : loss of some translucency and elasticity
Scales : starting to dry and curl, not abundant
Smell : pleasant and fresh with no hint of ammonia or sourness.
6 - 7 days on ice
Eyes : sunken and general cloudiness of pupil
Skin : continued loss of sheen and lateral line less distinct
Gills : thickened slime with blood diffusing into it, briny and malty odour
Flesh : translucency lost, soft and flaccid
Scales : almost non existent
Smell : briny, bready and malty.
9 - 10 days on ice
Eyes : either flat and cloudy or swollen and bloodshot
Skin : dull and pale looking
Gills : bleached in patches, much more thick, dark maroon slime, strong stale celery odour
Flesh : waxy in appearance, sticky
Scales : non existent.
12 - 16 days on ice
Eyes : either flat and cloudy or swollen and bloodshot
Skin : covered in yellow slime
Gills : thick slime, offensive odour
Flesh : considerable darkening of fillet, very soft, mushy, offensive smell
Scales : non existent.
Fish should be purchased daily wherever possible, the medium size fish being less coarse than large ones and more flavourful than small ones. Wastage from filleting is 50% for flat fish and 60% for round fish; round fish having larger head to body proportion, this therefore must be considered when deciding whether to purchase whole fish or fillets.
The following steps are also recommended for maximum shelf life :
1 : If necessary wash fish to remove scales or foreign matter
2 : Always gut fish before storage.
3 : Prepare storage container by : Placing a layer of ice on the base, cover ice with a sheet of plastic, place fish on plastic sheeting, cover with another sheet of plastic and cover with ice
4 : Store in a chiller and replace ice as it melts
5 : If the fish has been stored on ice for more than 2 days wash the fillets before cooking.
The term shelf life refers to the time period that fish can be stored before it is considered unpalatable. Fresh fish has a maximum shelf life of 12 days; beginning from the time it is caught or approx. 7 days from date of purchase. However, it must be remembered this is entirely dependant on the storage temperature being maintained at O°C; a fish loses 1 day of shelf life for every hour it sits at room temperature.
Remember that most chillers are set at 4°C, not 0°C thereby reducing the shelf life by maybe 50%.
PURCHASING AND STORAGE OF FROZEN FISH
Frozen fish is extremely useful and convenient. The type of fish you want may not always be available chilled. As long as you have purchased wisely; from a supplier of good reputation, the cooked fish should be indistinguishable from chilled. This is due to advances in technology, that allows the fish to be blast frozen on board the trawlers just minutes after being caught, thereby retaining all the fish's fresh properties. In many cases frozen fish is of better quality than chilled which may have been incorrectly handled and stored.
Frozen fish is generally packed in 10kg cartons. The fish should either be layer packed with sheets of plastic inbetween or the fillets individually wrapped. It is unwise to purchase fish frozen in block form as it will be difficult to separate the fillets.
Before you buy or use frozen fish, open the cartons and check the following :
1. The pack itself should be intact and free from any damage
2. Fillets should be solidly frozen with no discolouration or brownish tonings.
3. The fish should not have any unpleasant odours; this would indicate poor quality, handling and previous storage, it is likely it has defrosted and been re-frozen.
4. Large amounts of ice or badly distorted fish / fillets is also a sign of defrosting and refreezing.
5. White or bleached patches on the flesh are a sign of freezer burn or dehydrated flesh.
Storing
Frozen fish needs the freezer set at -18°C, this is suitable for short term storage only; a maximum of two months. Commercial freezers can hold fish at -30°C; this ideal for long term storage because the denaturation of proteins, oxidation of fats and enzyme or bacterial action are all reduced greatly at this temperature.
It is far, far better to buy commercially frozen fish than to freeze your own. This is because to retain all assets of the fresh fish it must be frozen rapidly, something a domestic or commercial freezer cannot do. If you have to freeze fish it must be of good quality, individually wrapped and used within a month of freezing.
DETRIMENTAL EFFECTS OF INCORRECT FREEZER STORAGE
Texture
Protein can be denatured by enzyme action. This means that the proteins lose their natural structure and thus their ability to hold water or moisture. Once thawed, the flesh drips excessively and looks dull white and spongy. When cooked the fish tastes wet and sloppy. Denaturation occurs if the freezing process is too slow or if the temperature fluctuates to any extent during freezing or storage.
Another detrimental effect of slow freezing is that water in the cells separates out and accumulates, forming large ice crystals which puncture cell walls. This results in changes in the texture in the flesh.
Minus 1.5°C to -3°C is the critical stage for freezing fish, as enzyme action increases markedly within this range. It therefore must be passed through as quickly as possible.
Oils
Fish oils will become rancid if the storage temperature is too high, if the fish has insufficient protective packaging or no ice glaze to prevent air from reaching the flesh. Rancidity effects the flavour and odour of the fish, these "off" flavours vary from mild cod liver oil to a burnt or paint taste.
Freezer burn
Freezer burn or dehydration occurs during frozen storage if the temperature fluctuates and there is air present inside the wrapping. On occasions the wrapper may be cooler than the fish and the moisture may leave the fish and condense on the inside of the wrapper. This moisture forms ice crystals in the package and the surface of the fish becomes white and dehydrated. The flesh when cooked becomes spongy and dry.
Thawing / defrosting
If you are forced to defrost fish (see cooking) then the only way is as recommended by the Health Authorities for defrosting any foods; covered in a refrigerator.
Cooking frozen fish
For maximum results, frozen fish is best cooked from frozen or while it is still icy (before it starts to drip). All that is needed is to adapt recipe to allow for a longer cooking time (approx. 25%) and a little extra moisture content.
