I did not know you can desalinate fishcakes until I read Karushio Reshipi [Lightly Salted Recipes], an eye-opening cookbook by the National Cerebral and Cardiovascular Center.
Fishcakes generally contain a high amount of sodium, and I had simply thought that we should limit consumption or avoid them all together.
Soaking time varies by size and type of fishcakes. The National Cerebral and Cardiovascular Center's cookbook suggests soaking for 15-20 minutes. My experiments show that soaking for 10 minutes is usually enough with heavier fishcakes that do not float on the surface of water and remain immersed.
When fishcakes are first cut into smaller pieces, the desalination process is faster.
Fishcakes that float in water, such as hanpen, take longer to desalinate. In my experiment, soaking a whole hanpen for 60+ minutes achieves similar desalination results as satsumaage (which sinks in water) after 15-20 minutes. Floating-type fishcakes also need to be immersed while boiling and soaking for efficient desalination.
Desalination can be done ahead of time. Remove fishcakes from water, and keep in the fridge until use.
More about fishcakes and my desalination experiments
To make fishcakes, salt is added to ground fish to get a supple, resilient texture (salt solubilizes myofibrillar protein, which facilitates setting as a gel).
Here are examples of fishcakes and their sodium content.
830 mg sodium/whole cake (85 g)
Satsuma Age, Shirakiku
230 mg sodium/piece (37.5 g)
240 mg sodium/piece (31 g)
505 mg sodium/piece (55 g)
165 mg sodium/piece (50 g)
According to my quick calculations of an oden recipe in the cookbook, desalination reduces the sodium content by approximately 90%. Responding to my inquiry, the hospital's clinical nutrition department said that there was no general desalination ratio but a number similar to results in the cookbook should be achieved if I followed their methods. The department also suggested checking the sodium content after desalination with a sodium meter, so I did.
Sodium meter (EISHIN EB-158P): Measures level of sodium content as a percentage (0.0%-5.0%) in food; it may be far less accurate than the hospital's sophisticated $1,600 sodium meter, but it is good enough to give you some idea.
The numbers below are not absolute, as measurements were done with regular kitchen tools and are subject to possible error in the sodium meter’s readings. Sodium content of samples before desalination is based on each product’s label.
Microwaved 4 slices in 100cc water, covered, for 1 minute, and let sit (covered while water is still hot and could evaporate).
In 5 minutes, water's sodium level showed 0.3% (translates into approx. 295mg sodium), and it went up to 0.4% (394 mg) in 7 minutes.
The sodium level remained the same afterward (last checked after 20 minutes).
Microwaved whole piece of satsumaage in 100 cc water (covered) for 1 minute, and let sit (covered while water is still hot and could evaporate).
At 10 minutes, the sodium meter indicated 0.2% (197 mg).
As expected, the sodium meter indicated 0.2% in 5 minutes of soaking.
Basically measured using the same method as kamaboko and satsumaage, except that hanpen was pressed down with another lightweight container while boiling and soaking.
The sodium meter indicated 0.2% (197 mg) in 5 minutes, 0.3% (295 mg) in 15 minutes, 0.4% (394 mg) in 35 minutes, and 0.5% (490 mg) in 70 minutes.
When hanpen was allowed to float while boiling and then immersed while soaking, it took 20 minutes to reach 0.2%, 80 minutes to hit 0.3%, and 5 hours to climb to 0.4%.
(Last updated: February 4, 2014)