Effect of time and method of harvesting on yield and quality of peppermint oil

Abstract

In the 1978-1979 season, two experiments using a completely random design were conducted to investigate, (1) the effect of time of harvest on yield and quality of peppermint oil, and (2) the effect of wilting period on oil loss and oil quality. In the first experiment, 13 harvests were carried out from January 3 to March 28, and followed by gas liquid chromatographic analysis of the oil. The best yield of high quality was obtained when the crop was harvested in the period between the last week of January and the first week of February, and plants were 10 - 20% in flower. At that time, oil yield and oil percentage were 113.7 kg/ha and 1.17% respectively, with the percentage of the principal constituents menthol 43.1%, menthone 28%, menthofuran 3.8%, menthylacetate 6.6% and cineole 4.1%. When the menthol content exceeded 43.1%, the oil yield declined steadily due to leaf senescence and shattering. In the second experiment, the peppermint crop was cut by windrow at 7 pm on February 16, 1979; samples were collected immediately following harvest, at 8 am, 2 pm and 8 pm for the next two days. The experiment was conducted when the crop was at full bloom stage, the oil loss during the wilting period due to leaf shattering was less than 5% and loss from other causes was 14.4%. The wilting period had no effect on oil composition. The effect of wilting period on oil quality was determined by the changes of menthoduran content in the harvested peppermint during that period. The results are discussed in relation to plant growth and development, rust development and to possible studies of peppermint in the future.