Improvement of Longan Drying Technique

During the second quarter of 2009, the Industrial Promotion Region 1 (IPC1) and GTZ requested cooperation from the Office of the Department of Agriculture (DOA) in Chiang Mai, the Agricultural Offices in Chiang Mai and Lamphun to organize a workshop on “Longan Dryer Development” for more than 428 dried longan producers and longan farmers to introduce new dryers for both peeled and pitted longan and unpeeled whole longan.  The workshop was aimed to enable them to improve their existing dryers by themselves, reducing their energy and labour costs and improving the quality of the processed longan.  DOA developed new dryer models to replace the widely used but inefficient conventional dryers, and in parallel developed a new drying technique.  GTZ was responsible for coordinating research and development with the production development teams from Chiang Mai and Mae Jo Universities and for consulting with GTZ experts in food drying technology.

For peeled pitted longan, the team designed a sealed dryer with adjustable temperature control. The drying temperature is maintained at 100ºC for the first hour, then reduced to 90ºC for the second hour, and further reduced to 65 ºC for the next 7 hours.  The 9-hour total drying time is thus 25% quicker than  the conventional drying method, which requires 12 hours.  Moreover, the quality of the processed longan is significantly improved; the new method results in fruit flesh which is dry with better colour retention, and also drastically reduces microbial count, with no fungal growth.  These simple improvements help the product meet stringent food safety standards.

For unpeeled whole longan, the DOA team designed a new model that is rather unconventional.  Unlike the open-tray dryer, it has a cover to minimize loss of heated air and permit bi-directional air flow: from  top to bottom and vice versa.  This design allows continuous drying and eliminates the shifting process.  The drying temperature is maintained at 110ºC for the first six hours and then reduced to 90ºC for the second six hours.  The temperature for the remaining 28 hours is maintained at 70ºC.  The total drying time is 40 hours, a significant reduction from the 48-50 hours required by the conventional method.  Shorter drying time leads to 17-20% fuel and labour cost reduction.  If all 428 workshop participants improve their existing 1,736 dryers, production costs can be reduced by 25 million baht for this season alone.  (This calculation excludes estimated savings from adoption by producers and farmers, the owners of 18,200 dryers, who did not attend the training programme).  GTZ anticipates that higher temperature and shorter drying times will lead to increased profits and now plans to collect data from farmers adopting this drying technique, during July and August 2009.