Soy sauce cakes contain about 5-10 wt% salt; therefore, incineration results in corrosion of the furnace and environmental problems related to, for example, dioxin generation. However, amino and organic acids, and soybean isoflavone, as well as a number of other useful components remain in the soy sauce cakes. The amount of desalination with water was 590 mg/10 g-feed, while that with methanol was about 70% of this value. Desalination could not be performed successfully with acetone or n-hexane. The amounts of flavonoid in the form of daidzein and genistein extracted from 10 g of soy sauce cake were 3.4-7.2 and 7.2-11.0 mg, respectively, while extraction with water was minimal. Moreover, the amount of flavonoids extracted increased while the amount of desalination decreased with aqueous alcohol solutions. The dual cylinder solid-liquid extractor presented here for separation of flavonoids and salt from soy sauce cakes was able to collect 10.2 mg/50 g-feed of daidzein and 18.8 mg/50 g-feed of genistein. The length of time the sample is retained in the mixer can be varied by changing the agitation speed, the number of baffle plates and the diameter of the mixer cylinder outlet. This solid-liquid extractor is therefore applicable in a wide range of food waste recycling processes.