foods
Editorial
Grain Storage: Theory, Technology and Equipment
Yan Zhao *, Haoxin Lv and Yanfei Li
School of Food and Strategic Reserves, Henan University of Technology, Zhengzhou 450001, China;
lvhaoxin0129@126.com (H.L.); liyanfei@haut.edu.cn (Y.L.)
* Correspondence: zhaoyanss10@126.com
1. Introduction
Grain is the basic material that guarantees human survival, and its security is inex-
tricably linked to the sustainable development and future destiny of humanity. Firstly,
this crop provides the body with the energy and nutrients necessary to maintain normal
physiological functions. It is rich in carbohydrates, proteins, fats, vitamins, minerals, and
dietary fiber, which are essential elements for ensuring human health and survival. Sec-
ondly, the abundant consumption of grain provides energy, which can support people’s
daily work and provide impetus for the development of human civilization. Thirdly, the
stable operation of agricultural production and the grain supply chain is crucial for social
stability and economic development.
The “Cereal Supply and Demand Brief” released by the Food and Agriculture Organi-
zation of the United Nations on 8 September 2023 predicts that world grain production in
2023 will reach 2.815 billion tons, an increase of 0.9% compared to last year. Although this
figure has been rising year by year, the latest report, “2023 The State of Food Security and
Nutrition in the World”, points out that there was no progress in addressing global food
insecurity in 2022, when an estimated 29.6% of the world’s population were moderately
or severely food-insecure. The total number of such individuals has reached 2.4 billion,
an increase of 391 million compared to before the COVID-19 outbreak in 2019 [1]. In
addition, under the combined influence of various factors such as conflicts, climate change,
and economic contraction, the complexity, fragility, uncertainty, and volatility of the in-
ternational grain supply chain have significantly increased. The stability and resilience
of global agricultural and grain industry chains are facing severe pressure. The current
Citation: Zhao, Y.; Lv, H.; Li, Y. Grain international situation emphasizes the importance of grain storage, and advancing the
Storage: Theory, Technology and technology involved is vital to ensure a stable quantity of good-quality stored grain.
Equipment. Foods 2023, 12, 3792.
https://doi.org/10.3390/ 2. Storage Environment and Grain Quality
foods12203792 Rice, wheat, and maize are the most produced and consumed staple cereal crops
Received: 25 September 2023 around the world. Rice and wheat are grown mainly in developing countries in Asia,
Revised: 11 October 2023 whereas maize is grown in developing countries of Africa, Asia, as well as South and
Accepted: 12 October 2023 Central America. In most areas of the world, food crops are seasonally produced and
Published: 16 October 2023 continuously consumed throughout the year. However, due to the limited agricultural
mechanization, it has been estimated that post-harvest quantitative loss during storage
reaches 15–25% [2]. Stored grains are easily damaged and consumed by insects such as the
lesser grain borer (Rhyzopertha dominica), maize weevil (Sitophilus zeamais), and red flour
Copyright: © 2023 by the authors.
beetle (Tribolium castaneum) and harmful fungi such as Aspergillus spp., Penicillium spp.,
Licensee MDPI, Basel, Switzerland.
and Fusarium spp. [3]. The suitable temperature, humidity, and gas composition of grain
This article is an open access article
storage environments will cause the growth and reproduction of pests and fungi. Kaita
distributed under the terms and
et al. adopted cold storage (5 ◦ C) to preserve rice grains and achieved good storage efficacy
conditions of the Creative Commons
Attribution (CC BY) license (https://
for a storage period of up to 24 months [4]. Lü et al. found that heat treatment could
creativecommons.org/licenses/by/
effectively control the infection of Tribolium castaneum adults in grain piles during the
4.0/). storage process [5]. Bilhalva et al. reported that integrated monitoring of the equilibrium
Foods 2023, 12, 3792. https://doi.org/10.3390/foods12203792 https://www.mdpi.com/journal/foods
Foods 2023, 12, 3792 2 of 4
moisture content and carbon dioxide concentration in a stored corn mass could inform
decision making on ideal storage time, loss reduction, and food safety [6]. Qu et al.
monitored quality changes in rice during nitrogen-modified atmosphere packaging storage
(N2 -MAPS), with the results showing that this process could delay rice deterioration [7].
Changes in storage environments have a significant impact on grain quality. In order
to maintain a high quality during the storage process, effective technologies should be
adopted to create a stable environment with the characteristics of low temperature, low
moisture, and low oxygen content.
3. The Application of Green Grain Storage Technology
Due to the significant impact of changes in storage environment on grain quality,
grain depots adopt different technologies to regulate conditions with the aim of effectively
reducing loss during storage, ensuring that the grain is free from pests and mold, stays fresh,
and has good flavor. Based on consumers’ pursuit of a healthy diet and the importance of
ecological protection in various countries around the world, green grain storage is highly
popular worldwide; this technology does not use synthetic chemicals and is typified by
low-temperature and controlled-atmosphere grain storage technologies.
Low-temperature grain storage technology mainly uses natural or artificial cooling
during the storage process to keep grain in the depot at a lower temperature, preventing or
slowing down the invasion of harmful organisms and the deterioration in quality. Based
on the climate characteristics of grain storage locations, methods such as renovating the
thermal insulation of warehouses, closed and covered grain, and natural or mechanical
refrigeration cooling are often used to reduce the temperature of grain piles. Ning et al. [8]
investigated the quality characteristics of rough rice under low-temperature warehouse
conditions using ambient cold air in winter. Four hundred tons of rough rice was stored
in the warehouse and aerated from top to bottom using ambient cold air in February. The
temperature was maintained below 15 ◦ C without cooling operations until the end of May,
and the quality of the rough rice was evaluated in October. The results indicated that
compared to ordinary-temperature storage, this method of using ambient winter air better
maintained the germination and quality of the rice, induced less change to physiological
activity, and resulted in fewer cracked kernels.
Controlled-atmosphere grain storage technology involves manually adjusting the air
composition inside the grain storage warehouse to prevent harmful organisms’ metabolic
activity, which controls pests, inhibits mold reproduction, reduces the intensity of grain
respiration and physiological metabolism, and delays the deterioration in quality. Cur-
rently, N2 controlled-atmosphere storage is the most widely used method worldwide,
using high-concentration nitrogen to replace air in grain piles. Therefore, grain depots
implementing this method generally need to purchase nitrogen production equipment,
such as carbon molecular sieve and membrane separation nitrogen generators, and require
airtightness modifications to the warehouse to maintain a high concentration of nitrogen
in the environment. Lorenzo et al. [9] found that when stored corn and wheat grains
were exposed to a highly purified N2 controlled atmosphere (98.5% ± 0.5), the growth
and sporulation of Fusarium graminearum, Fusarium langsethiae, Aspergillus flavus, and
Fusarium verticillioides and Aspergillus aflatoxin production were significantly reduced.
4. Green Grain Storage Equipment
Based on the theory of a grain storage ecosystem, the operation mode of temperature-
and air-controlled storage, which apply a combination of controlled-atmosphere and low-
temperature storage technology, has become the development direction of the field of
green grain storage. In a green controlled atmosphere, modern electronic technology
and nitrogen supply equipment are harnessed to regulate the supply of nitrogen and sift
the air in grain bins through molecular sieves, increasing the nitrogen concentration [10].
The molecular sieves form an air loop with the grain bin, and the nitrogen concentration
in the air in the bin remains above 98%. Carbon dioxide gas-controlled grain storage
Foods 2023, 12, 3792 3 of 4
systems include a carbon dioxide gas supply system, a detection system, gas circulation
facilities, pressure regulation equipment, an oxygen respirator, a grain monitoring and
control system, and a mechanical ventilation system. In addition, during the grain storage
process, grain-cooling machines or specialized air conditioners are used to keep the grain in
a lower-temperature environment in order to prevent or slow down the invasion of harmful
organisms and the deterioration in quality [11]. Internal loop flow temperature control
technology accumulates cold sources in the grain pile in winter, and utilizes the supporting
circulation equipment installed in the warehouse during the high-temperature season to
circulate and equalize grain’s temperature through the operation of the warehouse pipeline,
grain pile, and ventilation cage. Therefore, utilizing green, efficient, safe, and energy-saving
technologies, continuously exploring the application of new equipment, and ensuring good
grain and oil quality represent the development direction of green grain storage technology.
5. Perspectives of Grain Storage
Today, due to the rapid growth of the global population and the occurrence of intermit-
tent and unexpected events, grain security is facing significant challenges. It is crucial that
more effective technologies and equipment are adopted to improve grain storage efficiency,
including minimizing the loss of quantity during the process and effectively maintaining
grain freshness. In addition, more attention should be paid to the application of “green
grain storage technology” to protect the global ecological environment.
This Special Issue aims to publish high-quality articles on grain storage, covering a
wide range of aspects including basic theory, the application of grain storage technology
and its impact on quality, and the development of new equipment for grain storage.
Author Contributions: Writing—original draft preparation, review and editing, Y.Z., H.L. and Y.L.;
funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript.
Funding: This research was funded by the National Key Research and Development Program of
China, grant number 2021YFD2100604-02 and the Cultivation Programme for Young Backbone
Teachers in Henan University of Technology.
Conflicts of Interest: The authors declare no conflict of interest.
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