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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Infrared Heating for Improved Drying Efficiency and Quality of Almonds and Pistachios

Location: Healthy Processed Foods Research

2013 Annual Report


1a.Objectives (from AD-416):
California produces about a million tons of almonds and pistachios annually and is ranked the top commercial producer of tree nuts in the United States. However, for each commodity about 3% production losses result from adverse weather conditions followed by improper drying practices. For almonds, the Almond Board of California has expressed an urgent need to develop a quick drying method to remove moisture caused by rain during harvest season to reduce quality deterioration and improve product safety. Exposure of almonds to wet conditions results in concealed damage, discoloration and unpalatable off-flavor. For pistachios, industrial sorting in water bath before air drying results in significant moisture gain on the nut surface. Quick drying of pistachios is vital to avoid shell staining, decay and microbial contamination. Current hot air drying practices have low energy efficiency and drying rates, high labor and energy inputs and do not guarantee safe products. The goal of this project is to develop a quick drying method that uses IR to partially dry almonds and pistachios followed by hot air drying. The new approach will reduce energy use and drying time and improve product quality and safety. Specific objectives addressed will be the study the drying efficiency and product quality under sequential IR and hot air drying (SIRHA); evaluation of the effectiveness of the new SIRHA heating method to perform simultaneous drying and decontamination of almonds and pistachios, and; quantification of energy saving and benefits of SIRHA heating methods compared to current drying practices.


1b.Approach (from AD-416):
In Year 1, we will design and modify current IR heating equipment to include new hopper, IR emitters, stirring rods, electric motor, speed controllers, HA drying stage and collecting containers. Also, we will start collecting freshly harvested samples. In Year 2, we will test performance of SIRHA and optimize processing parameters. Test effect of SIRHA on product quality and pathogen inactivation: The product quality, including color, shelf stability, sensory characteristics, and microbial load of dried almonds and pistachios will be determined and compared with those dried with traditional drying methods. In Year 3, we will evaluate the effects of new drying method (SIRHA) on drying characteristics and energy consumption. We will transfer new technology through research presentations at different conferences and workshops; publicize the SIRHA system through the USDA ARS information system; final report of the research project and at least two peer reviewed publications will be available for information dissemination.

Industry partners will be identified for promoting and using the new processing technology through close collaboration with the Almond Board of California and California Pistachio Board and processors.


3.Progress Report:

Progress reported addresses Objective 2: "Develop sustainable infrared technologies that can be used for process- and energy-efficient blanching, dehydration, pasteurization, and peeling of specialty crops" of the parent project. To study the drying efficiency and product quality under sequential Infrared (IR)and hot air drying (SIRHA), a new device with capacity of both infrared and hot air heating has been designed and is under manufacturing. The new IR and hot air dryer has accurate temperature and air flow control system for achieving desired drying performance and improved food safety. It is expected that the new drying method will reduce drying time, energy consumption and risk of salmonella contamination.


Last Modified: 10/24/2014
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