Sefa Tarhan

Peppermint Drying Performance of Contact Dryer in Terms of Product Quality, Energy Consumption, and Drying Duration

Drying is a commonly used postharvest operation for medicinal and aromatic plants. Their high initial moisture contents, requirement of moderate drying temperatures, and quick deterioration of their quality attributes make their drying processes energy intensive and time consuming. These properties may also cause the dried product to be of heterogeneous quality. A contact dryer that transferred energy to drying plants mainly by heat conduction was developed and tested by mixing or not mixing batches of 15 kg of chopped peppermint plants. The contact dryer had three main operational units: a drying table, a mobile mixing/aeration car, and a control panel. The contact dryer was operated with one of four drying programs. All programs affected the completion duration of drying, essential oil content, and dried product color differently. The shortest drying time (15 h) was obtained using the drying program of gradually increased water temperature from 55–60 to 75–80°C in 6 h and mixing/aeration. However, mixing and aeration changed the product color slightly more and partially increased essential oil loss. These drawbacks can be alleviated by selecting the appropriate duration of mixing and aeration. The menthol and menthone percentages of fresh peppermint essential oil ranged from 31.02 to 34.02% (average value: 32.52%) and 23.23 to 26.47% (average value: 24.85%), respectively. The menthol and menthone percentages of dried peppermint essential oil ranged from 22.74 to 42.07% and from 8.95 to 21.76%, respectively. The significant variations in the essential oil composition of dried peppermint leaves within replications were possibly caused by the variations associated with the age and cutting order of fresh peppermint plants at harvest.

Airflow Channeling Through Fixed Wheat Straw Bed in an Updraft Gasifier Before the Initiation of Gasification

Channeling is an operational problem of updraft gasifiers used to gasify cereal straw. Airflow distribution within a fixed straw bed before the initiation of gasification was investigated to understand the channeling. Absolute pressure deviations in the central plane of the straw bed were determined to check the uniformity of airflow distribution, because pressure was the driving force of airflow. Airflow channeling occurred through the straw bed even before the initiation of gasification. Superficial velocity through the straw bed inversely affected the uniformity of airflow distribution while machine-chopped straw and straw bed depth improved it.

A New Way to Improve the Drying Kinetics and Final Quality of Peppermint

Abstract Drying is the most common postharvest process to preserve medicinal and aromatic plants. Peppermint has a high worldwide commercial value. Newly harvested peppermint plants were dried by using four different drying air temperature profiles. They were constant 35°C, constant 55°C, incremental rises from 35°C to 55°C in four hours, and in eight hours. The samples were dried down to the final moisture content for 8 to 18.5 hours. The fastest drying was obtained with the use of the constant 55°C and the slowest drying was obtained with the use of the constant 35°C. The incremental rise of drying air temperature profile from 35°C to 55°C within 4 hours shortened the drying time by 46%. Page’s equation excellently represented all drying curves. Maximum color change and essential oil loss occurred with the drying at 55°C; however, incremental rise of drying air temperature over time reduced the extent of color change and essential oil loss. The highest essential oil change was -21.95% for the constant 55°C, the lowest essential oil change was -2.32% for the constant 35°C. The temperature of heated air affected the composition of peppermint essential oil. Drying at constant 55°C kept menthol content (43.31%) close to that (47.64%) of fresh peppermint but decreased menthone content (26.24%) and increased cineol content (8.18%). Considering the length of drying time and dried product quality values, the profile in which the drying air temperature rise within 4 hours was found to give the best results.

Design Parameters of Low Temperature Shelled-Corn Drying in the Central Black Sea Region of Turkey

ABSTRACT Corn drying is an energy-intensive process. Thus, the management of energy use is critical for economical corn drying. The Central Black Sea Region covering Amasya, Çorum, Ordu, Samsun and Tokat provinces has climatic and agronomic conditions suitable for corn production. However, the drying of newly harvested wet corn stays as a major problem for farmers since it is traditionally dried by spreading it on the ground in open atmosphere. Low temperature drying was selected in this computational study to dry corn safely. Fan power, heating power, total electric energy need of fan and total heating energy needed and to dry 1 ton corn from 25% (wb) initial moisture content to 13% (wb) final moisture content were estimated in September, October and November for each province. The airflow requirements (i.e., 159.1 m3·ton−1h−1 for Amasya) and overall electric energy needs of selected fans (i.e., 27245 kJ·ton−1 for Amasya) in September are more than in November (68.3 m3·ton−1·h−1 and 10221 kJ·ton−1, resupectively) because of quick deterioration of wet corn associated with high air temperatures in September. On the other hand, heating power requirements showed a mixed trend while the total heating energy needs consistently increased for all provinces when the drying operation was moved from September to November. In conclusion, the estimated total heating need increased while the estimated total electric energy need of fan decreased since the heating process increased the adiabatic drying potential of air, which in turn reduced the amount of air volume having to be flown through corn in the drying bin.