The second step of making corn starch
soak
In the corn soaking method, several or dozens of metal tanks are generally connected and combined with pipes, and the soaking water is circulated between the tanks with a water pump, and the soaking is countercurrent.
The trial results of adding soaking agent in soaking water show that lime water, sodium hydroxide and sodium bisulfite are not as good as sulfur dioxide, and the content of sulfur dioxide should not be too high. Because the dispersing effect of SO2-containing soaking water on the protein network is enhanced with the increase of SO2 content. When the concentration of sulfur dioxide is 0.2%, the protein network disperses properly, and the starch is easier to separate; but when the concentration is 0.1%, sufficient dispersion cannot occur, and the separation of starch is difficult. Generally, the maximum is not more than 0.4%, because the concentration of sulfur dioxide is too high and the acidity is too large, which is not good for corn soaking. On the contrary, it will inhibit lactic acid fermentation and reduce starch viscosity.
The soaking temperature has an important influence on the soaking effect of sulfur dioxide. Increasing the soaking water temperature can promote the soaking effect of sulfur dioxide. However, if the temperature is too high, the starch will gelatinize and cause adverse consequences. Generally 50 ~ 55 ℃ is appropriate, so as not to cause gelatinization of starch granules.
Soaking time is also closely related to soaking effect. During the soaking process, the soaking water does not penetrate into the inner tissue from the epidermis of the corn kernel, but enters the kernel from the loose tissue at the root at the bottom of the kernel, and penetrates into the kernel through the porous tissue of the bottom layer of the bran. Therefore, it must be ensured that enough soaking time. After corn soaked at 50℃ for 4 hours, the germ part absorbed water to the highest value, and after 8 hours, the embryo body part also absorbed water to the highest value. At this time, the corn kernels become soft, and after coarse crushing, the germ and bran can be separated. However, the protein network has not been dispersed and destroyed, and the starch granules cannot be released. If you continue to soak, the protein network can be dispersed. After soaking for about 24 hours, the protein network of the soft embryo body was basically dispersed, and after about 36 hours, the protein network of the hard embryo body was also dispersed. Because the dispersing process of the protein network is to expand first, then transform into small spherical protein particles, and finally the network is destroyed. So to fully disperse the protein mesh, more than 48 hours of soaking time is required.
Corn soaking conditions are not exactly the same in different factories. The general operating conditions are as follows: the concentration of sulfur dioxide in the soaking water is 0.15 to 0.2%, and the pH is 3.5. During the soaking process, the sulfur dioxide is absorbed by the corn, and the concentration gradually decreases. The concentration of sulfur dioxide in the finally released soaking water is about 0.01-0.02%, and the pH value is 3.9-4.1; the soaking water temperature is 50-55 °C; the soaking time is 40 to 60 hours. Soaking conditions should be determined according to the quality of the corn. Usually, old corn stored for a long time has low moisture content and hard corn requires stronger soaking conditions, that is, higher sulfur dioxide concentration, temperature and longer soaking time.
After the corn is soaked, the moisture content should reach more than 40%.