What's the difference between second-class corn and third-class corn?

There are three national quality standards for corn in China, namely, the most basic national standard for corn, the national standard for feed corn and the national standard for industrial corn. These three standards are interrelated and have their own characteristics. The national standard of corn is the general standard of bulk corn, which is widely used in the purchase, storage, transportation, processing and sales of commercial corn. Feed corn standards and industrial corn standards are more targeted, and there are some changes and adjustments on the basis of national corn standards. The similarities of these three standards are as follows: moisture, impurities, imperfect grains and moldy grains are the main indexes to measure the quality of corn; The difference is that besides the main indexes such as bulk density, feed corn also increases the technical indexes of crude protein, while industrial corn abandons the bulk density index.

Generally speaking, the indexes such as bulk density, impurities, moisture, imperfect grains and moldy grains are the most basic and important indexes to measure the quality of corn, which are widely representative and authoritative.

There are the following differences in maize quality in different producing areas in China:

(1) bulk density

In normal years, the bulk density of corn in northeast Inner Mongolia is the highest, and the quality of corn in Tongliao and Chifeng is basically above the second grade, with the first grade accounting for 90%. More than 70% of Jilin corn is second-class; The quality of maize in Heilongjiang is average, 60%-70% can reach the third class; 50% of corn in Liaoning can reach the second category, and 80% can reach the third category. But the bulk density of corn is greatly influenced by the year. For example, in 2003, due to the weather, the moisture content of corn was high and the bulk density decreased. The second-class corn in Jilin Province only accounts for about 50% of the total output, and most of the corn in Heilongjiang Province is unqualified.

In normal years, the corn in Shandong and Hebei in North China is basically above Grade II, especially in northern Shanxi and northern Xingtai, Hebei.

(2) Moisture

In normal years, the moisture content of corn in Northeast China is 28%-30% when it is harvested, and it is as high as 35%-40% in poor harvest years. The moisture content of corn in Inner Mongolia is slightly lower, generally around 24%, sometimes reaching 27%-28%.

Due to the cold weather in winter in Northeast China, the proportion of natural air-dried corn is small, except Tongliao in Inner Mongolia and southwest Liaoning, most of which are air-dried corn. There are two main drying methods. One is directly drying to about 14.5%, and the water gradually loses below 14% during storage. The second is to dry it until the water content is about 20%, and then dry it. The first method is mainly used for corn listed before the Spring Festival in Northeast China. Because of too much precipitation, it is easy to cause corn grains to shrink and the packing density is low. The corn listed after the Spring Festival mainly adopts the second method, which is naturally dried for a long time in advance, so the seeds are full and the bulk density is generally high. Under normal circumstances, the grain depot only reduces the water content to 14.5%, so it is difficult for northeast corn to reach 14%: 10,12 within three months. In April and May of the following year, after several months of natural water loss, the water content may sometimes drop further during the transportation from the place of origin to the sales area. As a national grain reserve, the moisture content of corn after drying is basically below 14%, and the highest moisture content does not exceed 14.5%. Some grain depots determine the drying effect according to the buyer's requirements, and the moisture index is determined by the buyer, generally between 13%- 15%.

Compared with the corn in Northeast China, the moisture content of corn in North China is lower at harvest, mostly around 18% to 20%, and the temperature is higher than that in Northeast China, which can reach below 15% in 5-6 days, so almost all of them use natural air drying for precipitation. In normal years, the water content of maize in Hebei is about 16%- 18%, and that of maize in Shandong is about 14%- 16%.

(3) impurities

Northeast corn is dried by machine, so the impurities are less, generally not more than 1%, and even less than 0.5% in some areas. Corn in North China is naturally dried, and a lot of impurities will be mixed in the drying process. Therefore, there are many impurities in corn in North China, sometimes exceeding 1%, which need additional screening.

(4) Incomplete grains

In the process of corn drying in Northeast China, the precipitation is too fast, which is easy to lead to crushing, and the mechanical operation also leads to an increase in the proportion of broken grains. At the same time, drying leads to the increase of heat loss particles, so the broken particles are generally higher than 5%. After a series of links such as storage, delivery, port transportation, loading and unloading, dumping, warehousing and delivery, the number of broken grains will increase, resulting in imperfect grains reaching 8% in general.

The corn in North China is naturally air-dried, with less broken grains, basically controlled within 5%, and the quality is only 2%. In spot purchasing, it is generally stipulated that the total number of defective products should not exceed 5%.

(5) Moldy grains

The moisture content of corn in Northeast China is very high at harvest time. If there is a lot of rain at harvest and the corn is not well kept and stored after harvest, it is very easy to cause corn mildew. In bad years, most corn moldy grains will exceed 2%, and some even reach more than 5%. Due to the limitation of storage environment and storage technology, small farmers can't store and ventilate in strict accordance with the standards, so there are few moldy grains in northeast corn before April, and the proportion of moldy grains will increase greatly after April. The content of moldy grains of corn in Inner Mongolia is low or almost zero, and it does not exceed 2% at most. Liaoning is slightly higher; The moisture content of maize in Heilongjiang is uneven, and the moldy grains are the highest. Shanghai Securities News