Technology Flash Talk: DryCard™ for dry chain management


Horticulture Technologies Poised for Uptake

DryCard™ for dry chain management

Anthony Phan, project analyst for the Horticulture Innovation Lab, presented this technology flash talk about the DryCard™ for measuring dryness and managing the dry chain during the Horticulture Research for Development Conference, "Colorful Harvest: From Feeding to Nourishing a Growing World," held March 26-27, 2019 in Washington, D.C.

Phan explained that drying is an age-old technique for preserving food and reducing food losses, but drying that is not done properly can have dire consequences. Products that are not dried below 65 percent equilibrium relative humidity can grow mold that may contaminate the products with harmful toxins such as aflatoxin. Consuming aflatoxin has negative health impacts and is associated with 30 percent of liver cancer cases worldwide. More than 5 billion people, particularly those in developing countries, are at risk of chronic exposure to aflatoxin in their diet.

To prevent mold growth and aflatoxin production during storage, producers can implement the dry chain – which is the system of drying products after harvest and packaging them in hermetic storage to preserve quality. In the cold chain, the focus is on maintaining low temperatures, so thermometers are used throughout the system to measure temperature. In the dry chain, the focus is on maintaining dryness, but what is used to measure dryness?

Large-scale producers use digital devices to measure relative humidity in dried products. But these can be expensive, and require batteries, regular calibration, and training, so they are often not used by smallholders. To determine dryness, smallholders typically rely on unreliable methods such as biting or touching the product. As a result, they use guesswork to determine if their products are safe from aflatoxin.

How does the DryCard work

A superior option is the DryCard™, a low-cost and simple tool for measuring dryness. The DryCard™ combines a strip of cobalt chloride paper (which changes colors depending on humidity) with a corresponding color scale that indicates the level of humidity. DryCards can be reused many times for up to 3 years and used for any dried products (such as dehydrated fruits and vegetables, seeds, grains and even meat or fish). Instructions and information are also printed directly on the card itself and can be translated to the local languages or presented pictorially.

The DryCard™ is simple to use. Enclose the DryCard™ in a sealed container with a sample of the product, wait 30 to 60 minutes, and then take a look at the color of the indicator strip. If the strip is a blue color, the food is dry and safe to store. But if the strip is pink, then the product is wet enough to potentially produce molds and aflatoxin.

Illustration shows 4 steps for using the DryCard, with a hand dropping seeds into a jar, the DryCard going into the jar, the jar closed for 30-60 minutes, and checking the color strip for dryness
Using the DryCard in 4 steps: First, add dried product to a container. Then add the DryCard to the container, and seal hermetically. Wait 30-60 minutes. Finally, check the color of the card for dryness.

DryCards can be paired with other postharvest technologies within the dry chain. For example, DryCards can be used with the Horticulture Innovation Lab's chimney solar dryer. They can also be used right before products are packaged with hermetic storage like the PICS bags to ensure that products are not reabsorbing moisture during storage. Or they can be used with drying beads, a zeolite-based dessicant, to monitor small or large scale seed storage.  

The DryCard can also serve as an instructional tool for teaching the effects of high humidity on food safety and food security. Several institutions and programs like the Postharvest Education Foundation have used DryCards in their classroom and in the field to build awareness of this issue and guide users to adopt better postharvest practices and technologies.

Scaling up the DryCard globally

To make the DryCard™ more widely known and available, the Horticulture Innovation Lab has partnered with in-country businesses to manufacture, market, and sell DryCards. Businesses and entrepreneurs can manufacture DryCards for 10–15 cents per card using locally available materials and equipment, and then sell them for $1 to $1.50 each. In a little over a year, the Horticulture Innovation Lab has set up in-country production and sales in 11 countries and has sold more than 22,000 DryCards.

DryCards give businesses a profit margin that enables a self-sustaining model while maintaining an appropriate price for smallholders. Accessibility of DryCards for users and profitability for businesses makes this technology ready for uptake.

Value Chain

Postharvest practices