Sensorial evaluation of the freshness of fish

AZTI has drawn up some 40 tables for freshness specific for the most important commercial species in southern Europe, including fish and shellfish. The sensorial method, known as QIM (Quality Index Method) and introduced into Europe some years ago, is being applied to a greater number of species, including some in the frozen state. Concretely, for species of interest in our waters, AZTI has specific schemes for each species of commercial importance that the inspectors use.

Evaluating the freshness of fish is a common and essential practice for the industry: Freshness is an attribute that is considered objective as defined by a combination of sensorial, physical, biochemical and microbiological parameters. The human senses play a fundamental role in this assessment, which we call sensorial evaluation.

The most important sensorial characteristics for raw fish are its aspect, including its colour, smell, and its texture. Besides, other characteristics related to the species, the origin, handling and intrinsic defects or produced during processing may be evaluated by sensorial means.

When we talk about whole fish, freshness evaluation is required throughout the whole commercial chain at the following junctures:

• At the dockside or market, the first classification as required by European legislation
• In the area of reception of raw material at the processing plants
• At different junctures during distribution-sales from wholesale to retail
• In specific cases such as quality control in companies involved in processing/canning of fish products.

The Quality Index Method (QIM) used by AZTI, is based on the objective evaluation of certain attributes of fresh fish (skin, eyes, gills, etc.) using a points system (from 0 to 3). No sample can be rejected based on just one criterion, given that several attributes are taken into account simultaneously. The total QIM points score is not influenced by small differences in the points for any one attribute. The lower the points score, the fresher the fish.