What Is the Quality Check Process for Mackerel?

According to a reference paper by the Torry Research Station (now UK DEFRA), mackerel are fatty fish and are not normally gutted at sea; therefore, mackerel spoil quickly unless they are chilled immediately after catching and kept chilled. Mackerel with a fat content of about 10 percent will develop odors after 1-2 days at 10°C, will be soft and spoiling rapidly after 3 days, and will be putrid after 5-6 days; fish with a higher fat content spoil even faster. Mackerel of medium fat content stowed in ice or in refrigerated seawater immediately after capture will keep in good condition for 4-5 days. Stale or noticeably spoiled mackerel should not be used for processing. The signs of stale fish are as follows:

• Eyes are sunken, cloudy, and discolored red or brown.
  

• The skin has lost bloom, and its colors have lost intensity and brilliance, giving a washed-out appearance.
  

• Gills are dark red or brown, and a dark blood red mucus oozes from the gill covers.
  

• The odor of the gills and body is sour, sweaty, or strongly oily; sometimes a smell of ammonia is also present.
  

Mackerel for freezing should be chilled immediately after capture and frozen within 24 hours; mackerel with high-fat content should preferably be frozen within 12 hours. Frozen mackerel, properly glazed and kept in cold storage at -30°C, will keep in good condition for at least 6 months. Cold storage life can be extended up to 1 year when mackerel are packed in polyethylene bags that are topped up with water and frozen in vertical plate freezers. The block is doubly protected against deterioration in-store by the encasing ice and by the packaging. Gutting before freezing is not necessary, and maybe a disadvantage.