Grain's Five Storage Problems

To improve grain storage, we should, first of all, understand the physiological characteristics and storage of grain. After being separated from the mother plants, the harvested crop seeds will remain viable for a long time. In other words, activities of life including respiration, after-ripening and aging will continue until the seeds finally lose vitality and die. 

Below is a summary of the five physiological characteristics of grain.

First, grain is a living organism, and its life span largely depends on its status when put into storage and the storage conditions. Maintaining seed vitality is crucial for the preservation of seeds. This is especially important for seed grain, as only living seeds can germinate and be used as seeds.

Second, grain can breathe during storage. Just like how people breathe, the seeds inhale oxygen and exhale carbon dioxide. Respiration is a necessary physiological activity to keep them alive. Once respiration ceases, the seeds would die.

Third, grain will continue to develop and mature for a period of time after harvest. This is a process called after-ripening. Newly harvested grain is generally not fully mature and will ripenin the early storage period. Respiration is active during this period. As the seeds are not fully mature, the germination rate is very low, and the processed product is not of very good quality.

Fourth, as we mentioned earlier, grain is a living thing that undergoes an aging process just like people. After-ripened new grain has a much higher germination rate, but its germination capacity fades away over time until it completely loses value as seeds.

Finally, germination can occur in grain. Germination refers to the process in which the embryo of grain and oil seeds resumes growth, and the young roots and buds grow out of the seed coat. After germination, the quality of the stored grain will deteriorate, mainly reflected in nutrient transformation. This will remarkably undermine food quality, process quality and processing yield and add to the difficulties in preservation.

Five storage problems arise due to the aforementioned five characteristics.

First, grain can turn sour. Grain contains free fatty acids (without sourness), acid phosphates, acid proteins and a small quantity of organic acids. Among them, unsaturated fatty acids are prone to oxidation, which generates sour and smelly substances.

Second, fatty acid oxides and peroxides generate unsaturated fatty acid methyl esters catalyzed by oxidase, resulting in bitterness in grain. Moreover, bitterness is attributed to a high fat content and low precision processing.

Third, grain has relatively loose colloidal tissues and cannot tolerate high temperatures. Exposure to strong sunlight or heat will increase the crack ratio and chances of discoloration, reducing food quality and process quality. High temperatures can also lead to higher fatty acid value and quality deterioration.

Fourth, as newly harvested grain is physiologically active and has a high water content, a large bacterial load and low porosity, it is difficult to dissipate the accumulated heat in the warehouse, resulting in heating in the grain piles.

Fifth, a higher water content and higher ambient temperature can cause the stored grain to self-heat. Catalyzed by enzymes, mold, mildew and yellowing can occur.