Temperature and moisture
Temperature and moisture are determining factors in accelerating or delaying the
complex phenomena of the biochemical transformation (especially the "breathing" of
the grain) that are at the origin of grain degradation. Furthermore, they have a direct
influence on the speed of development of insects and microorganisms (moulds, yeasts
and bacteria), and on the premature and unseasonal germination of grain. In the
general diagram of conservation designed by Burges and Burrel, the relationship
between temperature and moisture content is established in order to determine the
area of influence of certain important degradation phenomena, such as: the
development of insects and moulds, and the germination of grain. It is easy to observe
that the higher the temperature, the lower must be the moisture of the grain in order to
ensure good conservation of the products. As an example, the preceding table shows
the recommended durations of warehousing, according to the temperature and
moisture content of the grain. The temperature depends not only on climatic conditions
but also on the biochemical changes that are produced inside a grain mass, provoking
undesirable natural heating of the stored products.
Micro-organisms
Micro-organisms (moulds, yeasts, bacteria) are biological agents present in the soil
which, when transported by air or water, can contaminate products before, during and
after the harvest. Their presence and growth cause severe changes in the nutritive
value and the organoleptic features of grain (taste, smell, aspect).Furthermore, they are
responsible for the alteration of important germinative properties of seeds (vigour and
capacity to germinate) and, in the case of moulds, for the potential formation of
dangerous poisons (mycotoxins).Impurities, and cracked or broken grains, foster the
development of micro-organisms. Furthermore, temperature and humidity have a
determining influence on the growth rate of these degradation agents. It has been
observed that micro-organisms develop at temperatures between -8°C and +80°C,
when the relative humidity of the air is over 65 percent. On the contrary, atmospheres
that are low in oxygen help check the development of these degradation agents.
Insects
Insect infestations can occur either in the field, before the harvest, or in the places
where products are stored. In some cases, these infestations are difficult to discern
with the naked eye, since the damage is provoked by the larvae developing inside the
grain. The insects most likely to infest stored products belong to the following families:
- Coleoptera (damage by larvae and adult insects);
- Lepidoptera (damage only by larvae).
Insects can be responsible for significant losses of product. Furthermore, their biological
activity (waste production, respiration, etc.) compromises the quality and commercial
value of the stored grain and fosters the development of micro-organisms. Insects can
live and reproduce at temperatures between +15°C and +35ºC. On the contrary, low
humidity slows or even stops their development, and a low supply of oxygen rapidly
kills them.
Rodents
Rodents invade and multiply in or near storage places, where they can find an
abundance of food. They cause serious damage not only to stored products but also to
packaging and even to storage buildings.The principal rodents, those most common and
likely to attack stored products, belong to the following species:
- black rat, also called roof rat (Rattus rattus),
-brown or Norway rat, also called sewer rat (Rattus norvegicus),
- Mouse (Mus musculus).
Prolonged attacks by these pests inevitably results in serious quantitative losses of
stored products. To these losses must be added those arising from the decrease in
quality of the foodstuffs, caused by the filth (excrement, secretions) rodents leave
behind in the stored products. This contamination is as important from the marketing
standpoint as it is for hygiene and health. Indeed, rodents are often the vectors of
serious diseases (rabies, leptospirosis).
NatalieR answered the question on May 24, 2022 at 06:44