Peppermint plants were initiated from rhizome cuttings (10 cm long) supplied by Jahad Daneshgahi in March 2009. According to the method described by Farahani et al., (2009), seventy five peppermint samples were notified above were transferred into pots (25 cm head diameter × 20 cm height) filled with sandy loam soil (soil average amount of 5580 gr in each pot). This experiment was carried out using a randomized compllete block design with 3 replications. The factors studied included 5 levels of water deficit stress that were D1 (100% field capacity), D2 (85% field capacity), D3 (70% field capacity), D4 (60% field capacity) and D5 (45% field capacity), respectively. In order to determine the soil moisture rate of 100% field capacity, 24 h after irrigation we selected 5 field soil samples by sampling drill, then samples were weighed by electrical scale and placed under 105 ℃ in electrical oven for 48 h. Field soil samples were selected for determination of soil moisture rate daily, than determined 85% field capacity, 70% field capacity, 60% field capacity and 45% field capacity, respectively.

Results indicated that drought stress motivated a significant reduction in all of the growth parameters and essential oil yield and percent. The highest values of growth parameters and essential oil percent and yield were observed under 100% field capacity (control). Also, the highest values of Mentone and menthofuran were obtained under 100% field capacity (control) and the highest values of menthol were obtained under 70% field capacity by using gas chromatography-mass spectroscopy (GC-MS).

The peppermint material was obtained from ten cultivation sites (four growers) around Le Mayetde-Montagne, Allier, France (altitude 400 to 800 m). The individual surface areas ranged from 0.6 to 2.5 ha for an overall surface of 8 to 10 ha. Planting density was 30,000 plants/ha.

A marked inversion of the menthol/menthone ratio was observed according to harvesting time. The late blooming period gave oils rich in menthol. A second harvest gave a high-quality oil and increased overall yield. Pre-drying did not affect the chemical composition of the oil obtained but allowed larger amounts of plant material to be distilled. In particular, Bouverat-Bernier showed an increase in oil yield up to flowering and a fall thereafter and an increase of levels of menthol and menthyl acetate while those of menthone decreased from June to September. For Hungarian peppermint, the levels of menthone were always greater than those of menthol regardless of harvest time.

Dry leaves of Menlba piperita L. 'Kliment-63' and 'Zefir' of 1997 crop were used.

The oil yield from 'Zefir' was 0.97% and that from 'Kliment-63' was 0.54%. The oil from 'Zefir' was found to be rich in menthol (46.2-50.2%) and menthyl acetate (16.8-22.5%). In the oil from 'Kliment-63,' the content of these components was lower, while the menthone content was higher (20.0-23.1%).