Salted Squid “Shiokara”
Fermented seafood boasts a rich and extensive past. Dating back to the 3rd century B.C., Erya, the earliest known surviving Chinese dictionary, documented the preservation of fish through fermentation with salt. Throughout history, preserving seafood has posed a significant challenge and played important roles, particularly due to the unpredictable nature of fish catches compared to stable farm harvests and livestock meat production. Since fresh fish are highly susceptible to spoilage and decay, a range of methods, including fermentation, have been innovated to address this issue.
Seafood can be processed using two primary methods to prolong its shelf life. The first method involves sterilizing the seafood and sealing it in packaging to prevent the entry of external microorganisms. Examples of this approach include canned seafood and fish sausages. The second method involves controlling factors such as acidity, salt content, moisture levels, temperature, and other environmental conditions to inhibit the growth of microorganisms. Another approach is to encourage the activity of microorganisms and autolytic enzymes, which break down complex organic compounds, such as sugars or carbohydrates, into simpler substances. This process is known as fermentation. Differentiating between fermentation and decomposition can be subjective, as we label the beneficial actions of microorganisms as fermentation and the negative effects as decomposition.
“Shiokara“ Salted Squid
Salted squid is a culinary delight prepared by combining squid meat with a small portion of liver and salt, and allowing it to mature for a specific duration, resulting in a distinctive flavor. This dish has enjoyed enduring popularity in Japan, especially when paired with sake, and its factory production experienced a significant surge in the late 20th century. As a result, among the various fermented aquatic food products, salted squid has garnered large attention and become a major subject of research and study.
Process of Salted Squid
A general manufacturing method is as follows. Remove the squid’s internal organs, etc., and cut the flesh into small pieces. Add about 1–10% liver. Add about 5–20% of salt. Stir once or twice a day and let it ripen for 5 to 10 days. During this time, the unique flavor is formed. In actual production, koji, various seasonings, and alcohols such as mirin and shochu are often added.
The maturation process of salted squid primarily relies on the autodigestive enzymes present in the squid meat, the digestive enzymes found in the liver, and the activity of microorganisms. Through these processes, amino acids, which contribute to the distinctive taste of salted squid, and volatile bases, which contribute to its characteristic aroma, are generated and accumulated. This transformation of flavors and aromas is a crucial and essential aspect of the maturation process.
Transformation of Salted Squid
Following charts describe how the squid meat transforms over time of maturation, as it is processed with different amount of salt added and kept at 25°C (77°F) without preservatives.
When 20% salt is added, squids become suitable for consumption between the 10th and 80th days of the maturation process. The first 10 days marks the point when volatile bases and free amino acids are produced at the highest rate. As the maturation progresses, the presence of microorganisms, predominantly Staphylococcus and Micrococcus, gradually diminishes and does not significantly contribute to the overall maturation process.
For squid that has undergone a maturation process with 15% salt, the optimal consumption period ranges from 7 to 40 days. During the initial stages, microorganism levels remain relatively stable, but around the 15th to 20th day, Staphylococcus bacteria begin to increase, resulting in a total microorganism count of approximately 10⁶ to 10⁷ per 100ml by the 50th day. The higher presence of volatile bases compared to the sample with 20% salt can be attributed to the increased activity of microorganisms during the maturation process.
The ideal period for consuming squid that has undergone a maturation process with 10% salt ranges from 5 to 20 days. In this sample, microorganisms exhibit significantly higher activity compared to those present in samples with higher salt concentrations. The microorganisms found in this sample include Staphylococcus, Micrococcus, and yeasts like Debaryomyces kloeckeri. These microorganisms contribute to the breakdown of proteins and the production of volatile bases and acids, resulting in higher levels of amino acids and volatile bases/acids in the squid preserved with 10% salt. Due to the increased presence of volatile bases, the pH level of the squid gradually rises above 7.0 during the later stages of the maturation process.
Amino Acids in Salted Squid
During the maturation process of salted squid, the decomposition of proteins in the squid muscles leads to an increase in the concentration of free amino acids. As discussed earlier, when a lower amount of salt is added, microorganisms become more active, resulting in a quicker generation of free amino acids, including Glutamine Acid (Glu). The following charts provide a comparison between salted squids with 13.7% and 7.6% salt added throughout the maturation period.
Microorganisms in Salted Squid
In addition to introducing autodigestive enzymes, the inclusion of squid liver in the flesh of salted squid serves as a protective measure against the proliferation of various microorganisms, such as squid putrefying/decay bacteria. The broad antibacterial properties of squid liver inhibit the growth of various microorganisms, allowing only certain dominant strains, including Staphylococcus and others, to thrive and increase in the salted squid environment. This characteristic contributes to the extended shelf life and the development of a robust and flavorful profile in salted squid.
