Effect of Distillation Time on Peppermint Yield and Oil Composition Jeffery B. Cannon, Thomas Horgan, Charles L. Cantrell, Tess Astatkie, and Valtcho D. Zheljazkov* C.L. Cantrell and J.B. Cannon, Natural Products Utilization Research Unit, Agricultural Research Service, United States Department of Agriculture, P.O. Box 8048, University, MS 38677; T. Horgan, Mississippi State University, North Mississippi Research and Extension Center, 5421 Highway 145 South, Verona, MS 38879. V. Zheljazkov, University of Wyoming, Sheridan Research and Extension Center, 663 Wyarno Road, Sheridan WY 82801; T. Astatkie, Department of Engineering, Nova Scotia Agricultural College, P.O. Box 550, Truro, NS, B2N 5E3, Canada. Received 19 Dec. 2010. *Corresponding author (vjeliazk@uwyo.edu). Peppermint (Mentha X piperita) is a common crop in Northwestern US and recently has been intensively studied in Mississippi. The essential oil is commonly extracted via steam distillation. However, there is no agreement in the literature regarding the optimal distillation time and no information on how the length of the distillation time affect oil yield and oil composition. This study determined the effect of distillation time (1.25 min, 2.5 min, 5 min, 10 min, 20 min, 40 min, 80 min, and 160 min) on essential oil yield, and the concentration and yield of eucalyptol, menthofuran, menthol, menthone, menthylacetate and t-caryophyllene. Essential oil yield increased from 2.5 min to 5 min. Numerically, greatest essential oil yield was achieved at 80 min distillation time, however, this was not different from yields at 20, 40, or 160 min. Our results suggest there is no significant increase in essential oil yield after 20 min of distillation time. The concentrations of menthol, menthone, and menthylacetate were not significantly affected by the length of the distillation time. The concentration of eucalyptol was greatest at the shortest distillation time, lower in 5, 10, or 20 min distillation time, and lowest at the longest distillation time (160 min), while the concentrations of t-caryophyllene and menthofuran followed exactly the opposite trend. With the exception of eculalyptol, the yield of the other constituents increased up to 20 or 40 min, and there was no significant increase after that time. Our results demonstrated that 20 to 40 minutes distillation time would be sufficient to obtain the highest essential oil yield with desirable essential oil composition.