Solar Drying of Lemongrass (Cymbopogon citratus) in Nepal

Abstract

Lemongrass (Cymbopogon citratus) is an aromatic herb with widespread use in food, medicine and herbal tea production. In Nepal, post-harvest losses of agricultural products remain a significant challenge, and solar drying has been identified as a practical and economical preservation method for small-scale farmers. This thesis investigates how indirect solar drying affects selected quality parameters of lemongrass, including drying uniformity, antioxidant capacity, essential oil yield, microbiological safety, and sensory acceptability. Shade drying was included as a comparative reference method to evaluate the influence of different drying conditions, particularly temperature, on product quality.

The lemongrass was dried in an indirect solar dryer in Dhulikhel, Nepal, reaching temperatures of 40-45 C and reducing moisture content from approximately 73% to 10% within 8-10 hours. Shade drying achieved a comparable moisture content over more than one week. Some variation in drying uniformity was observed, with the bottom tray of the right column consistently showing higher final moisture content, possibly due to differences in fan performance between the two columns of the dryer.

Antioxidant capacity, measured by DPPH assay, decreased slightly upon drying regardless of method, with solar and shade drying producing comparable results. Essential oil yield was approximately 70% lower in solar-dried leaves compared to fresh leaves, though considerable biological variation between batches limits the reliability of this finding. Both drying methods met WHO microbiological limits for herbal products, and no bacterial growth was detected in brewed tea under aerobic or anaerobic conditions. SEM analysis suggested that solar-dried samples potentially retained more intact glandular trichomes (the microscopic oil-storing structure on the leaf surface) than shade-dried samples. In the focus group, solar- and shade-dried teas were generally rated higher than commercially dried and fresh lemongrass teas for aroma and flavor by Nepalese participants, whereas no significant differences were observed among Swedish participants.

Overall, solar drying appears to be a promising method for processing lemongrass, preserving quality parameters at a level comparable to shade drying while offering a dramatically shorter drying time.

Popular Abstract

Every year, large quantities of food are lost before they ever reach a plate. For small-scale farmers in Nepal, this is a daily reality. Crops harvested with care can spoil fast due to limited access to preservation technologies. Solar drying offers a simple and affordable solution, where energy from the sun can be used to remove moisture from food, extending its shelf life without the need for electricity or expensive equipment.

This thesis investigates whether an indirect solar dryer, a dryer that circulates solar-heated air rather than exposing the product to direct sunlight, could effectively dry lemongrass while preserving its quality. Lemongrass is a widely used aromatic herb in Nepal, valued both for its flavor in cooking and its use as a herbal tea with traditional medicinal properties.

The results showed that the solar dryer could dry lemongrass within 8-10 hours, which is a dramatic improvement compared to traditional shade drying, which took over a week to achieve the same result. But speed alone is not enough. The important question was whether the quality of the lemongrass was preserved in the process.
The dried lemongrass met international microbiological safety standards, and importantly, no bacteria were detected in the brewed tea, meaning the final product is safe to drink. The antioxidant capacity, which reflects the health-promoting properties of the plant, decreased slightly after drying but to a similar extent regardless of whether solar or shade drying was used. This suggests that the higher temperatures of solar drying do not cause significantly greater nutritional loss than simply drying at room temperature.

A sensory study conducted with focus groups in both Nepal and Sweden found that the solar- and shade-dried lemongrass teas were generally preferred over commercially dried alternatives in the Nepalese group, suggesting a local market potential. Among Swedish participants, no clear preferences were detected between samples, which may reflect differences in familiarity with lemongrass as a product.

Some challenges remain. Drying was not perfectly uniform across all positions in the dryer, and the essential oil content was considerably lower after drying compared to fresh leaves. More research with larger sample sizes is needed before firm conclusions can be drawn.

Overall, the findings suggest that indirect solar drying is a promising approach for processing lemongrass in Nepal, offering a faster, hygienic, and quality-preserving alternative to traditional drying methods, with potential benefits for both farmers and consumers.

• author: Hultén, Mathilda
• supervisor: Federico Gómez Galindo
• organization: Pharmaceutical Technology (master); Food Technology and Nutrition (M.Sc.)
• course: KLTM06 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences
• keywords: solar drying, lemongrass, Cymbopogon citratus, indirect solar dryer, food preservation, Nepal, drying uniformity essential oil, antioxidant capacity, microbiological safety, sensory evaluation, dried lemongrass, post-harvest processing, food engineering nutrition and food chemistry
• language: English
• id: 9235961
• date added to LUP: 2026-06-12 14:09:34
• date last changed: 2026-06-12 14:09:34