Peppermint plants, cultivated in Japan, belong to Mentha arvensis, L. and it is the most excellent species in the world, that its essential oils contained the highest yield 80-90 %, of l-menthol. Having long studied the Japanese peppermint oils, the writer perceived much inferiority of the smell and taste of the Japanese menthol crystals to that of the foreign trade. General menthol manufacturers in Japan, however, seem to care only of appearance, that is color and a crystalline form, of the menthol by their experience. The progress of menthol products was prevented probably because that they did not criticise the goods in view of the chemical points.
The writer has been studying, especially, the aroma and taste of the Japanese menthol crystals. The menthol crystals of Japan are recrystallized with dementholized oils, therefore it is obvious that the menthol crystals are accompanied by an aroma and a taste of the solvent. Hence, we must decide to improve the aroma and taste of the peppermint oils prior to menthol crystals. The ordinary refined Japanese peppermint oils have a bitter taste together with a proper disagreeable odor, besides they are colorized on keeping which decreases severely the value of the articles.
The writer has commenced the research, for the purpose of the contribution to promote the Japanese peppermint industry, in view of manufacturing the superior peppermint oil after investigating the bad constituents.