Peas are among the most important vegetables that are canned or preserved in glass in Europe. They are also sold frozen. This vegetable cannot be eaten raw. Peas naturally contain a toxin that is deactivated by cooking them. Fresh peas are only available in June and July. The annual plant (Pisum Sativum) on which peas grow, belongs to the Fabaceae family.
Peas have a hard pericarp (fruit wall) which is inedible, therefore, the peas should be shelled.
There are two types of seeds, namely round peas and wrinkled peas. This difference is caused by the starch composition. Round peas only contain amylose, while the wrinkled peas also contain amylopectin. As a result, are the wrinkled peas sweeter and tastier. The round peas, however, do have a more aromatic pea flavor and can be sown in early in comparison to the wrinkled peas.
There are long and short straw straw peas. The plants with long straw can be 1 to 2 m in length and are, therefore, in need of the necessary support during the cultivation. In the manufacturing sector, only short straw varieties are used.
The peas in cans and glass are classified in terms of size.
|Extra fine||1 of 0||< 7.5|
|Very fine||2 of 1||7.5 – 8.2|
|Fine - round||3 of 2||8.2 – 8.7|
|Fine - wrinkled||3 of 2||8.2 – 9.3|
|Middle fine - round||4 of 3||8.7 – 9.3|
|Middle fine - wrinkled||4 of 3||9.3 – 10.2|
|Middle II - round||5 of 4||> 9.3|
|Middle II - wrinkled||5 of 4||> 10.2|
In general, fine and medium fine peas are processed together with carrots.
Peas are very healthy. They contain a lot of vitamin B1, B2 and C, iron and dietary fiber.
The peas are sown during spring, at the latest in May. Depending on the variety and time, 90 to 110 seeds per m2 are sown at a distance of 10 cm between the rows. When sowing early the highest seed quantity is used.
Peas grow best in mild climates with enough humidity, ensuring that during flowering and ripening sufficient moisture is present. Preference is given to a humus rich and humid soil. The plant has the ability to absorb nitrogen from the air through Rhizobium bacteria, that living in symbiosis in the root nodules on the roots of the plant.
Since peas are only harvested from mid-June to mid-July, it is in the processing plants’ interest that the pea supply is spread to a maximum over this period. To achieve this coverage, sowing is done according to a specific timetable, also called seed scheme. Moreover, advantage can be taken of early and late varieties of peas. ?During ripening sugar is converted into starch, allowing the peas to become harder. In addition, the grain skin hardens. The ideal time for harvesting can therefore be determined using a tenderometer. This measures the force required to perforate a sample of peas. The peas are ready for harvesting when the tenderometer value is between 100 and 130. The round peas are at the time of harvest light green of color. Wrinkled peas both come in light green and dark green varieties. When the tenderometer value is too high, too much sugar is converted to starch. It will be harder to cook the peas, they have a lesser flavor and there is a bigger chance of a murky brine.
The peas are harvested mechanically. During threshing, both the crop is mowed with mobile threshing machines as well as with stationary threshing cabinets in the factory. When using mobile equipment, the crop is mowed and moved to a large threshing drum. This threshing drum opens the pea pods through friction and the peas are separated. Next, using sieves, the peas are separated from the straw and transported to the factory.
After harvesting the peas must be processed as quickly as possible to prevent them from warming up. warming up might cause the peas to be affected by bacteria, which convert proteins into toxic brown matter. Therefore, the temperature of the peas is well monitored.
To determine the detergent effect of the washer, the percentage of unwanted parts is determined, also called tare. This percentage is also included in the price of the raw material.
Often, coarse dirt is first removed with shake and drum sieves and a blower. Because peas are quite vulnerable, a flotation washer is used. The peas are fed into the machine through a funnel. In the first part of the flotation washer the remaining coarse and heavy dirt particles are removed. The stream that is formed at the bottom of the washer is so strong that only the heavier parts sink. In the second part of the washer, bark, leaves and pea peels are sorted because they are lighter than the soaked peas and therefore float to the surface of the water. Using a strong flow of water, the now soggy and sunken peas are pressed to a vibrating sieve screen. Here, any remaining pea peels are loosened and the remaining sand is washed away.
With a conveyor belt or water the peas are transported to the sorting machine. Here, the peas are sorted according to the above mentioned classifications. Sorting is important because a pea’s size determines its further processing, the difference in filling weight, starch content and price.
The peas sorter consists of 3 to 5 rotating clover leaf-shaped, perforated drums with a diameter of about 2 meters that are placed on top of each. With water, the peas are led to the upper drum which has perforations of 8 mm. The sieved peas are collected in a gutter and transported with water to a drum with perforations of 7 mm. The peas with a diameter greater than 8 mm are sorted using two drums according to size in groups of fine, medium fine and medium II. Sometimes the coarser peas are sorted based on their starch content. In order to do this, the peas are added to a brine solution where the peas with a higher starch content and therefore a higher density sink to the bottom.
After sorting, the peas are blanched. Depending on their size/ sorting classification, the peas are heated up to 75 to 80°C for 2 to 4 minutes. After that, the peas are immediately washed with cold water, preventing growth of thermophilic microorganisms. In addition, this step removes any starch from the peas, making sure that there will not be any turbid water. Blanching removes any cell moisture from lightly crushed peas, which may otherwise cause flavor inconsistencies when coming in contact with oxygen.
Peas can be filled in canned with an internal protective lacquer layer or glass pots. When using glass pots with a ventilating lid a partial vacuum is created after sterilization and cooling. A non-ventilating lid may also be used, whereby the vacuum is created through steam injection. The filling process is usually carried out using a telescopic filler, this allows for the filling volume to be adjusted. The filling containers are filled with the product; after which they are placed exactly above the glass jars or cans to be filled. The product falls through a filling opening in the package, after which a hot covering liquid is added. This covering liquid consists of a 1% saline solution with a small amount of sugar. Because finer peas result in a higher filling weight, they will also have a higher weight after draining.
The pots and cans are then sterilized in an autoclave. In addition, cans can also be sterilized in a continuous sterilizer. The cans are sterilized with steam, the pots in water. To prevent leaking of the covering liquid during sterilization and cooling, pressure regulation for the glass jars with ventilating covers is required.
Depending on the filling volume, sterilization must be done at 121°C (half liter) for 16 minutes or at 121°C (liter) for 18 minutes. After this step the containers in the sterilizer are cooled down to a core temperature of about 35°C.
The peas should be stored dry at a temperature of about 10 to 15°C. Usually the cans and jars are labeled only after leaving the temporary storage.
After the blanching and cooling steps, the peas are frozen on a conveyor belt freezer using cold air (-35°C), which is blown over the belt. In this way, the peas are frozen in a short period of time (IQF, individual quick frozen). The peas can be stored in bulk and later packaged using a flowpacker.