Over the last few weeks I have had conversations with many agriculture and food industry stakeholders, including many small-scale producers and traders that have been left holding on to excess inventory due to distribution interruptions related to Covid-19. Many lack the proper storage facilities and are gravely concerned that their products are going to go to waste prior to the markets opening back up. That being said, I thought I would share some easy tips and technologies that smaller operators can employ to protect their products from losses during the covid-19 crisis and beyond.
The Dry Chain is the Solution
Food products are generally relatively warm and wet when harvested but have very short storage lives in that state. In fact, we know that for every 1% increase in seed moisture content or 5ºC increase in storage temperature, the life of a seed is cut in half. The "Dry Chain" is a term coined by our team to refer to the initial dehydration of dried products followed by hermetic storage in moisture-proof packaging until use. This is analogous to the cold chain for fresh produce, in which products are maintained under refrigeration throughout their supply chain. The Dry Chain has been found to be an effective solution to reduce losses and improve quality in dried products and can be employed by following the below principles.
Tip: Think of your seeds or grains as a clock with a finite amount of ticks. The longer they are exposed to moisture and warmth, the faster the clock is going to tick and they are going to be lost.
Remember that High Humidity is the Enemy
The moisture content of seeds and grains equilibrate to the ambient relative humidity (RH) of the air to which they are exposed. Bacteria and fungi depend on water to grow, but cannot do so below about 65% RH, while insects are unable to survive below 35% RH. Thus, assure that your products are dried below these levels to prevent microbes and/or postharvest pests.
Another general rule of thumb for adequate short and medium-term storage is a combined relative humidity (RH) and temperature (ºF) value below 100.
Your Work Is Not Done After Drying
One of our goals at Dry Chain America has been to educate people on the importance of humidity control during storage and distribution. As I mentioned above, the cold chain is synonymous with the postharvest management of fresh produce. However, outside of long-term storage (think, genebanks) dried products do not require refrigeration and often times refrigeration can increase the susceptibility of the products to mold growth in the future. Instead, products should be placed into hermetic, moisture-proof containers for storage and distribution. If properly dried and hermetically stored, the products can then be kept under ambient conditions for one to two years without losing much, if any viability. This makes the Dry Chain a highly effective strategy to prevent postharvest losses in low-resource environments, as no further energy or infrastructural requirements are required to maintain quality after initial drying as long as the integrity of the storage container is maintained.
Innovative Tools to Implement the Dry Chain
Following harvest, the initial moisture level of the product should be checked. This is usually accomplished via moisture meters, however these instruments are often not available to consumers. To combat this problem, the Horticulture Innovation Lab at UC Davis created the DryCard, which is a low-cost, simple tool for checking the dryness of a product. If products are dry and safe for storage, then a blue color will be shown, but a pink color indicates products are not dry enough and are susceptible to mold growth.
If you do wish to know what the moisture content of your seeds is you can also download our Moisture Content Calculator here, which will provide you with your seed moisture content (SMC) as determined by the equilibrium relative humidity and temperature.
In environments where commodities can be dried below at least 65% RH, drying by sun or air drying may be sufficient. However, for those located in more humid regions, further drying is often necessary. If you lack drying facilities, value mobility, or are working with products that are susceptible to the effects of heated air drying, Drying Beads are a great alternative drying option. The Drying Beads are a modified ceramic product that can dry seeds, grains, pulses or horticultural products without heat. Following the drying cycle, the Drying Beads can be reactivated and used indefinitely, making them a cost-effective drying option as well.
Traditional storage methods involve the use of porous fabric bags, otherwise called jute bags, that are inadequate in preventing moisture from reentering the dried product. Instead, consumers should opt for new hermetic storage technologies that are now commercially available in many parts of the world. These can range from the multi-layer plastic bags produced by companies such as PICS or GrainPro to plastic and metal drums or even sealed jars for smaller quantities.
Tip: Stick a DryCard inside your storage solution of choice so that you can track any changes to the internal environment and take action if it becomes necessary.
One-third of the food produced for human consumption is lost or wasted, with the majority of losses occurring in developing nations between harvest and the consumer due to poor postharvest management practices. During these trying times it is of the utmost importance that the food chain remains safe and operational. If you are struggling with losses, I would encourage you to follow the practical guidelines outlined above as well as in the adjoining chart.
Bradford, K. J., Dahal, P., Van Asbrouck, J., Kunusoth, K., Bello, P., Thompson, J., et al. (2017). The dry chain: Reducing postharvest losses and improving food safety in humid climates. Trends in Food Science & Technology, 71, 84-93. (Link)