Fish – how fresh does it need to be?

Two recent sensory studies conducted by the Icelandic and Norwegian members of the European Sensory Network (ESN) examine consumer and food experts’ quality ratings of cod and salmon.


“How do consumers judge the quality of fish?” This was the question proposed by a research group led by Kolbrun Sveinsdottir and Emilia Martinsdottir from Iceland’s MATÍS Research Institute [1]. Together with colleagues from Denmark, the Netherlands, and Ireland, the researchers tested 378 consumers from these four countries all of whom had indicated they ate fish at least once a month. The subjects were served eight samples of cooked cod, and graded them on a nine point preference scale. Then the researchers asked the test subjects about their personal fish consumption habits, including purchase and consumption frequency, and motives and barriers of fish consumption, along with their food and health attitudes in connection with the perceived importance of fish as a health food. Parallel to the study, a trained sensory panel set up a sensory profile of the cod products.

The sources as well as the means and length of storage of the cod samples varied: two samples came from farmed cod, the other samples came from wild cod. There were two samples each of fresh fish (stored for either three or six days), modified atmosphere packaged (MAP) fresh fish (stored in MAP for either three or ten days), and cod that had been frozen for a period of nine days or five months.

Freshness is not the most important point for everyone

When the data
were analysed the researchers found five basic consumer groups with different preferences. In every country the preferences were represented with various strengths.

A relatively small group of those questioned (10 percent) generally did not like the cod very much, and rated most of the samples  negatively. These particular consumers most likely preferred fish frozen for only a short time because of its more neutral sensory characteristics. The majority of this group were Danish, but a few were Icelandic and Irish.

14 percent of the consumers gave fresh fish the highest value. They indicated a marked preference for wild-catch produce, and rejected fish that had had a long storage period. The majority of this group were Icelanders and Netherlanders, with a few Danes.

A surprisingly large number of consumers (22 percent) preferred the fish that had been frozen for a longer period. These samples had a darker colour, were somewhat musty, and had a dishrag-like smell. The taste was slightly fishy and amine-like, reminiscent of dry salt-cured fish. Especially the Irish consumers were not bothered by the discernable freezer smell of these products, presumably because they have a tradition of consuming frozen fish.

Approximately the same number of consumers (23 percent) showed themselves to be real friends of farmed cod. Most notably, its meaty texture flavour, and odour, and the light colour satisfied many of the Danes and Icelanders.

The largest group, 32 percent of the consumers, found no difference between the various cod types. They rated every product positively. There are a high number Irish and elderly people in this group. They consider eating fish to be healthy, and give fish consumption a very positive general rating.

„The overall highest preference within the study were for frozen cod products of both short and extended storage time,“ concluded study director Kolbrun Sveinsdottir.  „This indicates that there are good marketing possibilities for these products.“   

How do chefs judge?

Norwegian researchers tested a special group of consumers who are particularly at home with food [2]. They checked whether chefs, as food experts, could clearly pre-rate raw fish filets (in this case salmon) as to what their qualities would be when they were cooked.

The researchers compared the chefs’ ratings of the raw fish with the ratings the trained sensory panel had assigned to the cooked salmon filets. The choices were between filets that had been stored at a temperature of four degrees Celsius for either 2, 9, 14, or 16 days.

By and large the chefs rated the quality of the fish filets similarly to the sensory panel when it came to deciding which filet was suited for consumption. Nevertheless, some of the ratings differed from one another: cooked filets that the panel had judged as clearly no longer edible were also rated by the chefs to be of poor quality; however, the chefs judged the filets to still be usable after a storage time of 16 days.

The cooks based their judgements strongly on appearance, whereas the panel focused on the difference in texture caused by variation in storage time in the prepared samples. The intensity of sea-water odour as well as sour and stale off-notes proved to be dependable indicators as to whether or not the fish is edible. Such  unpleasant odours are more noticeable with cooked fish than with raw fish. “The chefs probably had the more difficult job in this case,” admitted study director Marit Rødbotten. “However, we expected them to give the samples of bad quality an evaluation and description that better correlated with the very bad quality of the cooked samples.” 


[1] Opens window for sending emailSveinsdottir K,  Opens window for sending emailMartinsdottir E, Green-Petersen D, Hyldig G, Schelvis R, Delahunty C: Sensory characteristics of different cod products related to consumer preferences and attitudes. Food Quality and Preferences, 20 (2009) 120-132

[2] Opens window for sending emailRødbotten M, Lea P, Ueland O: Quality of raw salmon filet as a predictor of cooked salmon quality. Food Quality and Preferences, 20 (2009) 13-23



Facts on fish consumption

  • Icelanders (still) eat the most fish overall (almost twice a week on average). With cod they prefer fresh wild cod, MAP-packaged cod, or cod that has only been frozen for a short time. They also enjoy eating traditionally cured cod.
  • Cod is especially popular in the Netherlands (above all as fresh fish), but also frozen cod is consumed twice as much as it is in Iceland or Denmark.
  • Icelanders and Netherlanders most often buy their fish from fish mongers, the Irish and Danes from the supermarket. 
  • The Irish stick to pre-prepared frozen fish dishes (but only once a month on the average), and traditionally eat more frozen than fresh fish.
  • Among the participating nationalities, Icelanders are the most convinced that fish is healthy, feel the least insecure regarding fish purchase and have easy access when buying fish. As opposed to the Danes and Netherlanders, they find fish not to be particularly expensive.
  • Young consumers have a more negative attitude towards fish. Fish bones bother them, they feel unsure by the purchase as well as the preparation, and like fish less than elderly people do.

Photo: R. Sturm /