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Generally, beans are stored in silos or steel bins at the local elevator (Figure 4.4) and are continually (and often continuously) monitored for storage stability prior to shipment. During severe weather changes in temperate climates, significant temperature gradients form within the bin or silo and, thus, moisture migration may occur within the beans. Therefore, it is important to provide continuous aeration (Navarro et al. 2012), to ensure that the beans are not molding or producing heat, and subsequently being damaged or developing musty off‐odors or off‐flavors.

Dry beans are conveyed to large storage silos or steel bins for interim or long‐term storage prior to additional cleaning. The central elevating system lifts beans from the receiving pit and deposits them on conveyors in order to fill the bins. Within each bin is a device termed a “bean ladder” that will enable beans to slide in a circular path to the bottom of the bin, thus minimizing seed coat damage. It is a general practice to monitor the moisture content within the silo and use airflow from the bottom of the bin proceeding through the beans and exiting either at the top or the bottom of the bin to improve equilibration and distribution of moisture. Beans are then subjected to density separation using a gravity table. Beans are screened for size, sorted for color using an electronic eye system, and finally, stored in silos or bins prior to packaging in bags or totes, or directly shipped in bulk rail cars or trucks for delivery (Sacklin 1985; Rodiño et al. 2011).

Beans may be subsequently air dried to less than 18% moisture to assure storage stability. Greater levels of bean moisture will result in intrinsic fungal spoilage. Such spoilage is characterized by a series of biological cascading processes that manifest as physiological heating, moisture migration and accumulation with subsequent catastrophic quality failure. Initiation of spoilage will migrate through the storage vessel and result in a significant product loss during dry bean storage. On‐farm storage in small bins is common; however, the vast majority of beans are handled in sophisticated commercial distribution systems designed with environmental monitoring and control devices (Grizzell et al. 1961).

Fig. 4.4. Dry bean receiving and storage elevator.

Fig. 4.5. Interrelationship of factors affecting the grain and microorganism respiration in storage.

Source: Kumar and Kalita (2017).

Figure 4.5 illustrates the relationship of the main factors affecting the respiration of grain, including legumes, and microorganisms in storage. Typically, the CO₂ concentration inside the bags is used as an indication of the biological activity of grains. Two factors affecting the movement of gases (O₂ and CO₂) in and out are bag’s permeability and the partial pressure of gases. On the other hand, gases concentration inside the bags is dependent on the balance between O₂ and CO₂ exchanges and the respiration levels of the biotic portion of grains. Higher initial moisture content of grains tends to facilitate increased CO₂ concentration due to higher respiration rates (Cardoso et a. 2008; Kumar and Kalita 2017).

Fig. 4.6. Interaction of grain moisture, storage temperature and equilibrium relative humidity at which different organisms can grow in storage.

Source: Bradford et al. (2018).

Three factors – moisture content of seeds, storage temperature, and equilibrium relative humidity (RH) – are the most important determinants of grains quality, as shown in Figure 4.6 (Bradford et al. 2018), including legumes (Sangeetha and Mohan 2020). Storage life of grains increases exponentially as the equilibrium RH humidity and temperature decrease (Bradford et al. 2018). Besides microbial and insects‐induced quality deterioration, the specific quality changes attributed to storage are associated with flavor (mustiness, sour/bitter), discoloration (browning, darkening), and “hard‐to‐cook” (HTC) defects (reduced imbibition, longer cooking time). It is well documented that under adverse storage conditions, storage defects such as “bin burn,” “hard‐shell” and HTC phenomena occur, resulting in a significant loss of bean quality and economic value (Paredes‐Lopez et al. 1989; Siqueira et al. 2018; Chu et al. 2020).

The improved utilization of dry beans can be maximized through a detailed understanding of the impact and control of postharvest handling, storage, and packaging. The overall final bean quality is directly associated with the control of critical physical, chemical, and biochemical processes during production and postharvest handling and storage (Uebersax and Siddiq 2012).