Ripening of Salted Herring



Salted herring products are of importance for the pelagic fish industry in the Nordic countries. The raw material for the production is herring ripened by salting in barrels for several months. The production is mainly based on tradition and human experience [Voskresensky 1965]. 

Although considerable research has been carried out in the Nordic and European community, the knowledge of the main factors governing the ripening process is still limited. During ripening, the herring obtains a unique taste and texture. A proteolytic degradation of muscle proteins, releasing peptides and free amino acids and the effect of salt on proteins are believed to contribute considerably to the sensory development. It is well documented that both digestive and muscle proteases participate in proteolysis during ripening [Nielsen 1995, Nielsen & Børresen 1997, Olsen & Skåra 1997, Stefansson et al. 2000]. However, it is unclear whether the digestive proteases only accelerate the process or lead to specific sensory characteristics. E.g. herring salted without intestines, also ripens [Stefansson et al. 1995]. Small peptides, free amino acids and free fatty acids are released during ripening [Engvang & Nielsen 2000, Olsen & Skåra 1997]and are believed to contribute to the taste of the salted herring, but no direct link between these compounds and taste has yet been proven. The sensory development is also influenced by other factors such as the salting process [Gudmunsdóttir & Stefansson 1997] and the herring stock used [Schubring & Oehlenschläger 1997]. 

Several Nordic institutes within fisheries research have been involved in collaborative projects in this field during the last decade. These institutes have carried out a number of salting experiments using herring from different stocks, caught at different seasons, etc. A tremendous amount of data is thus available. Even though the institutes have been collaborating in Nordic and European research projects, the different institutes have approached the studies from slightly different angles. Some have extensive knowledge about sensory attributes of the products, while others have focused more on results concerning the biochemistry behind the ripening process. Data from storage/ripening experiments with salted herring have been collected at The Danish Institute for Fisheries Research, Dept. of Seafood Research (Abbreviated Denmark/Den in the following), The Icelandic Fisheries Laboratories, Iceland (abbreviated Iceland/Ice) and NORCONSERV, Norway (abbreviated Norway/Nor) in the period 1992 to 1995. The results reported here are part of a project, described in a separate report[Nielsen et al. 1999].



Collection and data analysis of all existing data from the different institutes has never been carried out before. Combining the data may make it possible to retrieve more detailed information about the ripening process. Some institutes have focused on sensory evaluation of products, others on chemical or physical descriptions of the ripening process. Only by combining the data from different locations can the full picture be obtained. E.g. making predictive models between common variables measured in all countries (pH, protein etc.) and specific variables of for example sensory attributes, enzymatic variation, peptides or similar may make it possible to understand the variation in sensory quality on a more fundamental level. This may e.g. lead to a better understanding of the ripening process, development of inexpensive indicator variables of industrial importance, better means for controlling and monitoring the ripening, etc. 


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The data are available in zipped Unscrambler ver. 7.6 format. Download the data. If you use the data we would appreciate that you report the results to us as a courtesey of the work involved in producing and preparing the data. Also you may want to refer to the data by referring to 


Rasmus Bro, Henrik Hauch Nielsen, Guðmundur Stefánsson, Torstein Skåra, A Phenomenological Study of Ripening of Salted Herring. Assessing homogeneity of data from different countries and laboratories; J. Chemom., 16:81-88, 2002


Nielsen HH, Bro R, Stefansson G, Skåra T, Salting and ripening of herring - collection and analysis of research results and industrial experience within the Nordic countries, TemaNord 1999:578, ISBN 92-893-0371-9, Nordic Council of Ministers, 1999.


Data (Unscrambler format)

Data (Matlab v.4 format)



Data from a total of twenty ripening experiments (Denmark: 10; Iceland: 7; Norway: 3) with a total number of 46 trial groups have been analysed. The experiments have been carried out in the period October 1992 to November 1995. Four different stocks were used: Kattegat herring (K), Icelandic summer spawning herring (I), Atlanto Scandic spring spawning herring (A) and North Sea herring (N). Five different types of raw material processing was examined in the ripening experiments: Beheaded (B), Beheaded and gutted (G), Fillets (F), Skinned fillets (Fs) and Clipfish (C). The different stocks and treatments were not distributed evenly between the three countries as evidenced in Table 1. All salting and storage has been done according to the same normal industrial practice in the three countries (see earlier reports[Stefansson et al. 1995, Stefansson et al. 2000]for details concerning this aspect). All ripening experiments have been carried out at 5ºC. 

Table 1. Overview of stocks and treatments of herring in the three different countries. For abbreviations see text above.














Common data

The common data mainly contain simple chemical and physical analyses that are measured by all three laboratories. These data form the common axis around which to draw inter-country conclusions. The variables are primarily basic measures of overall properties of the brine and the fish such as analyses of proximate composition. Table 3 describes the variables. Names of variables are written as abbreviations. The last letter in most of the variable names refer to whether the variable has been measured in brine (B) or in the fish muscle (M). For some variables almost a third of the observations are missing, but for most variables only few observations are missing. The missing variables are generally randomly missing; that is, no overall objective caused specific analyses to be skipped. For some pH measurements it is known, though, that these were skipped at certain points in an experiment time due to stabilization of the pH. This aspect has not been pursued further here. Mostly, practical time-considerations simply prevented all analyses from being performed.

            The variables have been measured to give an overall description of the raw material, final product, physical and chemical changes taking place in the herring during the ripening process and furthermore to ensure that samples taken for analyses during a ripening experiment are comparable and representative.

Table 3. Explanation and abbreviations of variables used.





Protein, muscle

Raw material/product


Protein, brine

Solubilisation of protein fragments and salt soluble protein


Ash, muscle

Salt uptake (salt content generally 1 % lower than ashM)


pH, brine

Previous studies have concluded that deviating pH values can indicate foul ripening


Trichloroacetic acid soluble nitrogen, brine

Level of small nitrogenous compounds and protein degradation products that is solubilised in brine. Smell of brine is a traditional quality parameter.


Trichloroacetic acid soluble nitrogen, muscle

Level of protein degradation (caused by enzymes)


Trichloroacetic acid index, muscle

Level of protein degradation relative to total protein content


Trichloroacetic acid index, brine

Level of protein degradation relative to total protein content


Water, muscle



Fat, muscle

Raw material/product


Reference List

  1.    Engvang K, Nielsen HH, In situ activity of chymotrypsin in sugar-salted herring during cold storage, Journal of scientific food agriculture, 2000, 80, 1277-1283.

  2.    Gudmunsdóttir G, Stefansson S, Sensory and chemical changes in spice-salted herring as affected by handling, Journal of Food Science, 1997, 62, 894-897.

  3.    Nielsen HH, Proteolytic enzyme activities in salted herring during cold storage. Ph.D. thesis, Danish Institute for Fisheries Research, Department of Seafood Research. Ministry of Agriculture and Fisheries, The Technical University of Denmark, Building 221, 2800 Lyngby, Denmark, 1995, 

  4.    Nielsen HH, Bro R, Stefansson G, Skåra T,Salting and ripening of herring - collection and analysis of research results and industrial experience within the Nordic countries, TemaNord 1999:578, ISBN 92-893-0371-9, Nordic Council of Ministers, 1999, 

  5.    Nielsen HH, Børresen T, The influence of intestinal proteinases on ripening of salted herring, Seafood from Producer to Consumer, Integrated Approach to Quality, (Eds. Luten,JB, Børresen,T, and Oehlenschläger,J), Elsevier Science B.V., Amsterdam, 1997, 293-304.

  6.    Olsen SO, Skåra T, Chemical changes during ripening of North sea herring, Seafood from Producer to Consumer, Integrated Approach to Quality, (Eds. Luten,JB, Børresen,T, and Oehlenschläger,J), Elsevier Science B.V., Amsterdam, 1997, 305-318.

  7.    Schubring R, Oehlenschläger J, Comparison of the ripening process in salted Baltic and North Sea herring as measured by instrumental and sensory methods, European Food Research and Technology, 1997, 205, 89-92.

  8.    Stefansson G, Nielsen HH, Gudmunsdóttir G,Ripening of spice-salted herring, TemaNord 1995:613, Nordic Council of Ministers, 1995, 

  9.    Stefansson G, Nielsen HH, Skåra T, Oehlenschläger J, Schubring R, Luten J, Derrick S, Gudmunsdóttir G, Frozen herring as raw material for spice-salting, J Sci Food Agric, 2000, 80, 1319-1324.

10.    Voskresensky NA, Salting of herring, Fish as food, Vol. III, (Ed. Borgström,G), Academic Press, New York, 1965, 107-131.


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