1. Process flow Raw material harvesting → Acceptance → Debriding, Filament → Inspection → Trimming → Rinsing → Threshing → Cleaning → Blanching → Cooling → Picking → Ice water precooling → Drainage → Quick freezing → Screening → Packaging → Refrigeration → Inspection
2. Operation points
(1) Raw material The best harvest time for harvesting sweet corn is the milk ripening period, which is 20 to 22 days after pollination. The pollination time is usually calculated when the maize ears spit about 1 inch (3.3 cm) of the filaments. Corn grain moisture content should be 70% to 73% when harvested. At this time, sweet corn has the best taste and flavor. Harvested corn can not stay in the field for a long time and exposure, do not squeeze too much during transport and handling, so as not to damage corn kernels.
(2) Acceptance of raw materials Acceptance of sweet corn should be bluish green when it is harvested. The grain is full, the color is yellow or light yellow, the color is uniform, there is no noise grain, the grain size and grain arrangement are even and tidy, and the phenomenon of baldness, lack of grains and insects is not serious.
(3) Peeling The dried sweet corn shall be placed in a cool place immediately after entering the factory and peeled and processed immediately. The processing time received from corn harvesting cannot exceed 6 hours. If it cannot be processed within 6 hours, it must be stored in a fresh-keeping warehouse at about 0°C for a short time. Manually strip the corn stalks and remove the corns. The ear of the corn that removes the loquat leaves should be taken lightly and put into a special basket.
(4) Trimming, selecting and grading first remove sweet corn spikes that are too old, too tender, excessively wormy, and extremely irregular in grain. The sweet corn ear with a few worms and variegated grains was used to excavate the insect pods and variegated grains with a knife. Then according to the diameter of corn, two or three grades can be formulated according to different corn varieties, and the difference between grades is set at about 5 mm.
(5) Cleaning and threshing Because quick-frozen corn kernels are not defrosted and washed prior to consumption, they must be washed with running water. The threshing is performed on a special corn thresher, and the thresher knife depth is graded with the depth of the knife to prevent the corn grain from being cut too deep or too shallow. Some cut too deep, may cut the corn cob, affect the appearance and taste of the product; cut too shallow, cut fewer grains, low yield, waste of raw materials.
(6) Bleaching and blanching is the most critical process in the processing of tender corn. It must be strictly controlled in the temperature and time of blanching. The role of blanching is the following: it can inactivate the enzymes in the corn tissue, because the low-temperature refrigeration will not make the enzyme lose its activity, still undergoing slow physiological and chemical reactions, so that the nutrients of the grain are destroyed; Hot can also kill some microorganisms and eggs, ensuring product hygiene and food safety; the air in the blanched corn kernels is squeezed out, reducing the expansion pressure at the time of ice formation during freezing, and increasing the resistance to the expansion pressure. Force, and correspondingly reduce the degree of oxidation of raw materials to maintain the product's color and nutrition. Bleaching can use boiling water or steam, the temperature is 93 ~ 1OO °C, according to the water temperature control blanching time, usually 3 to 8 minutes. If the blanching time is too long, the nutrients will be seriously lost, and the quality indicators such as the color and texture of the finished product will be greatly reduced. The threshed corn grains should be blanched immediately. Blanching can be done in a sandwich pan or a continuous blancher. The method of blanching is to boil the boiled water and put it in sweet corn. The ratio of water to corn kernels is 4:1.
(7) Cooling the blanched corn kernel should be cooled immediately, otherwise the residual heat will seriously affect the quality, such as darkening the color, increasing the consumption of dry energy, increasing the quick freezing time and wasting energy. It also provides the conditions for the reproduction of microorganisms. Therefore, the cooling must be timely and thorough to ensure the product's color and quality. In order to save water, a sub-stage cooling method can be used. First, use a spray method to reduce the temperature of the corn kernels at about 90°C to 25-30°C; then, soak and cool in the ice water at 0-5°C, so that the temperature at the center of the corn kernels falls below 5°C.
(8) Pick and pick out cobs, filaments, discoloration particles and other foreign substances. In order to ensure product quality, improve productivity, reduce the pressure of pre-packaged screening, after cooling, manual selection on the conveyor belt, remove excessively cooked, not permeated and broken corn kernels.
(9) Leaching to drain can remove the moisture on the surface of corn kernels, prevent the formation of ice blocks and adhesion between corn kernels due to excessive moisture during freezing, affect the appearance and net weight, and also reduce the consumption of electrical energy. Draining can be carried out on a shaker, but it is best to dry it with cold air, drain it thoroughly, and secondly, it can be cooled further.
(10) Quick freezing and quick freezing are decisive factors in ensuring product quality. The faster the freezing speed, the better the product quality, whereas the longer the freezing time, the worse the quality. Fast-frozen corn kernels use a fluidized bed type quick-freezing tunnel. The corn kernels are laid flat on the conveyor belt. Multiple fans under the conveyor belt blow the cool air down from 6 to 8 m/s to make the corn kernels suspended. The temperature at the center of the corn kernels can reach -18°C. . The frozen corn grains should not stick to each other and the surface is frost-free. If the machine's evaporation temperature is -34 ~ -40 °C, cold air temperature -26 ~ -30 °C, the thickness of corn kernels is 30 ~ 38 mm, frozen for 3 to 5 minutes to meet the requirements.
(11) Screening Frozen corn kernels are further selected, defective grains and crumbs are removed, and sieved if necessary.
(12) Packaged frozen corn kernels should be packaged at -6°C. It is generally packaged in polyethylene plastic bags and packaged as 250 g/bag or 500 g/bag as needed. Sealed after packaging, at the same time marked on the seal production date, immediately sent to the refrigerator after packing.
(13) The temperature of refrigerators should be below -18°C and relative humidity from 95% to 98%. The temperature fluctuation range in the refrigerator cannot exceed 2°C. Otherwise, recrystallization and ice sublimation occur when the temperature fluctuates too much, which increases the ice crystals inside the corn tissue and destroys the cell structure, thus affecting the product quality. When the code is released, there must be enough space between the cymbal and the cymbal to facilitate air circulation.
3. Quality Standard
(1) Sensory index color: light yellow or golden yellow; Morphology: uniform corn kernel size, no broken kernels, regular incision of corn kernels; Impurities: no corn silk, temporal lobe, and other impurities, no frost return in packaging bags Taste, taste: simmer with boiling water for 3 to 5 minutes, and then taste, should have the sweetness and aroma of the sweet corn varieties, crisp and refreshing.
(2) Physical and chemical indicators Copper (calculated as Cu) ≤ 5.0 mg/kg, Arsenic (calculated as As) ≤ 0.5 mg/kg, Lead (Pb) ≤ 1.0 mg/kg.
(3) Hygiene indicators Microorganisms meet commercial aseptic requirements.
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