Getting a (Drying) Bead on Crop Preservation

When crops are harvested, they often contain too much moisture to be stored safely, making a drying step necessary. While farmers in developing countries typically use air drying, humid climates and rainy seasons can hinder their efforts, leading to high postharvest losses. Drying Beads technology is an alternative that works in even the most challenging tropical environments.

Johan Van Asbrouck of Rhino Research, a Thailand-based seed technology group, originally developed Drying Beads to preserve crop seeds. In humid environments, mold and enzymatic reactions (including sprouting) can plague farmers who harvest and store a portion of their grains, pulses, and groundnuts for use as the next season’s seed.

If commercial oven drying is available, the higher temperatures required to overcome the high relative humidity of the incoming air reduce seed viability and can even cause scorching (Bradford et al. 2018). Desiccant drying with Drying Beads is a gentle, heat-free process that preserves seed viability and the quality of delicate crops.

Drying Beads are small balls of modified aluminum silicates (known as zeolites) that have a crystalline, porous structure that can trap water. Drying Beads can absorb 20%–25% of their weight and are fully reactivated when heated to 230°C (446°F) for two hours (Rhino). Once the water is driven off, they can be used again, with no loss of drying capacity.

To use Drying Beads, farmers must place them in a hermetically sealed container with the seed or crop. For a small container, farmers would add a thick layer of the beads at the bottom, before adding the crop. For a larger container, like a drum, they would insert a perforated plastic column of Drying Beads in the center.

The Dry Chain

Drying Beads are one component of a quality system known as the “dry chain”—a term advanced by Kent Bradford of the USAID Feed the Future Innovation Lab for Horticulture at the University of California, Davis. With the tagline, “Make it Dry, Keep it Dry,” the dry chain system makes use of a range of tools, including a decision chart to determine when air drying would not be sufficient and a color-changing cobalt chloride indicator strip, called a DryCard, to monitor relative humidity inside the closed container (UC Davis).

In 2017, the Horticulture Innovation Lab, in partnership with Rhino Research, completed a successful pilot in Bangladesh that trained over 70 employees at 14 seed companies in the use of Drying Beads (Dawson 2017). The companies dried and stored 200 tons of seed with Drying Beads, providing access to high-quality seed to an estimated 100,000 Bangladeshi farmers (Dawson 2017).

Another approach involves use of a rural dry chain center, which dries and stores farmers’ crops for a fee and manages reactivation of the beads with electric or gas ovens. However, trained farmers can do their own drying and reactivate the beads wherever an oven is available. (In Guatemala and Mexico, farmers are using bread ovens at local bakeries). Rhino Research is also exploring microwaves and solar technologies.

Besides preserving seeds, Drying Beads are effective at maintaining the flavor, aroma, and color of high-value crops and have been tested on herbs, chili peppers, and shrimp (RR Drying Beads). There is also potential to expand into grains, nuts, and vegetables.ft