In order to utilize sweet potatoes for the material of Takju, brewing experiments with raw sweet potatoes, sweet potato chips powder and its koji were conducted; and various tests were carried out on effect of the treatments of acid, alkali, polyphenol oxidase inhibitor, oxidizing and reducing agents upon the prevention against coloring of sweet potato chips by steaming, and on peeling effect of sweet potatoes by the alkali and heat treatments. The results obtained were as follows.
1) In the case of brewing with raw sweet potatose, each plot showed low acid and ethanol content, and its finished Takju had an undersirable color and odor. The plots which were mashed after peeling showed higher ethanol contents than the plots mashed without peeling.
2) In the case of brewing with sweet potato chips powder, each plot contained considerably more amount of ethanol than the plots brewed with raw sweet potatoes, white it contained less amount of acid. The ethanol contents of the plots using wheat bran koji were 10.5∼11.4 per cent 4 days after mashing, and were higher than those of the plots using malts powder. Their finished Takju was inferior in quality because of the lack of acid and being darkened gradually in process of time.
3) The kojies which were made of sweet potato chips powder with Neurospora sitophila or Aspergillus oryzae had good appearance, but the Takju mashes brewed with these con tamed remarkably less amount of ethanol.
4) Effect of the treatments of acid, alkali, polyphenol oxidase inhibitor and organic solvents such as ether and ethanol upon the prevention against coloring of sweet potato chips was not recognized. Alum and burnt alum were effective a little on the decolorization, and among the oxidizing and reducing agents tested, potassium permanganate was most effective.
5) Darkening of sweet potato chips powder in course of heating after mixing with water was not affected by pectin and amino acids, but by tannin.
6) Sweet potatoes were not peeled easily by friction after soaking in the boiling solution of 3 per cent alkali for 6 minutes and peeled in boiling water for 12 minutes.
From the viewpoint of the results above mentioned, it seems to be necessary to study further on the isolation of microorganisms which are able to decompose the coloring substances and yeasts which are adequate for the fermentation of sweet potatoes in order to utilize sweet potatoes for Takju brewing, because brewing with raw sweet potatoes, sweet potato chips powder and its koji was unsuccessful, and effect of the various treatments on the decolorization of sweet potatoes was not recognized.
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