Processing procedure for chips and crisps
Destoning and peeling
Cutting / slicing
Blanching and drying
Blanching and freezing
Destoning is undertaken to deliver clean potatoes for peeling. The aim is to eliminate stones and other debris that can render the final products which are unsafe and could hamper the processing by disturbing the functions of the machines.
At a semi-automated processing company, the potatoes are pushed through a water bath. Stones fall down and the swimming potatoes are grabbed out by a conveyor belt. The water in the destoner is changed regularly to prevent cross-contamination. This washing step is used as buffer, so that the vessels remain in proper order, to guarantee ‘first-in-first-out’. At a small scale processor the destoning process is manual as well as the peeling that follows. After peeling the potatoes are washed with fresh cold water. Thus for a modernized crisps process, a crate dumper, destoning vertical screw elevator, rod washer, and a hydrometer for testing dry matter would be required for destoning. For peeling, a batch or continuous peeler with an inspection belt is required. An additional option is the inclusion of a size grader and knife to halve large potatoes.
There are different peeling techniques for manufacturing chips. The smoothest peeling is done by steam in the steam peeler. After the skin is loosened by the steam, the de-skinner removes and collects the peel waste and is then washed clean prior to being inspected. The Vessel peeler is commonly used in the Kenyan potato industry. By rotating the skin is removed mechanically. The third type of peeler is using blades in a rotating drum. For chips processing, a steam peeler, washer (preferably combined), and an inspection belt are needed. The process of destoning is largely the same in the manufacturing for crisps and chips. In a modernized process the potatoes move along a conveyor belt powered by gentle vibrations into a vertical helical screw conveyer, which allows stones to fall to the bottom and pushes the potatoes up to a conveyor belt to the automatic peeling machine.
The potatoes are cut or sliced into the desirable shapes and thickness at this stage of the process. While cutting and slicing, a good practice is to ensure the removal of starch from the surface of the slices as well as nubbins and slivers.
In crisps manufacturing, the potatoes pass through a revolving impaler/presser that cuts them into paper-thin slices, between 1.7 – 1.85mm in thickness. Straight blades produce regular chips while rippled blades produce ridged potato chips. The slices fall into a second cold-water wash that removes the starch released when the potatoes are cut. Some manufacturers, who market their chips as natural, do not wash the starch off the potatoes. Medium scale processors generally use an automatic cutting machine while a small scale processor does the slicing manually by using a traditional chopping board. This process is labor intensive, and sometimes does not yield uniform sizes and shapes of crisps.
In the case of chips, the cutting process is performed by either a hydro-cutting or mechanical cutting system. These machines cut the potato into strips–crinkled or straight, to the desired size, and then pass the cut pieces through equipment that removes imperfections, and undersized pieces. This equipment is, however, expensive (about USD 1million). Current processors in Kenya cannot afford this on their own. Access to loan facilities for banks will therefore be of significant assistance. The cutting process at a semi-automated processor mainly is mechanical. Small scale processors use a manual process of pushing peeled potatoes through a grid one by one. The operator presses the grid manually to cut each potato into the pieces required. This process is not only labor exhausting but also has a low throughput. A recommended upgrading could involve the acquisition of new cutters (new electrical cutters designed for large hotels/restaurants) which are already in the market, or fabrication of an improvised mechanical cutter with a feeder, a washer, and silver separator appropriately attached. A sorter with a cutter could also be added to halve large potatoes, thereby increasing the size of potatoes.
Blanching improves the texture and produces a more uniform color of the final product. Blanching of French fries inactivates the polyphenoloxidase enzyme, a result of which enzymatic discoloration in par-fried products is avoided. Blanching also helps to reduce the absorption of oil as well as the frying time because the potato is partially cooked during blanching. After blanching, the slices are pre-dried. This is to reduce the level of moisture that enters the fryer. Drying has additional benefits of reducing the frying time and oil usage, energy consumption during frying, and improves crispiness of the final product.
The potatoes are treated chemically to enhance their color, by immersing the slices in a solution that has been adjusted for pH, hardness, and mineral content. Often, the crisps caramelize during frying. In addition, there is mainly no testing of sugar levels to determine appropriate blanching time.
The blanching system uses screw blanchers, in which strips are gelatinized and the sugar levels reduced, after which they go through the dipping belt, into the hot water before being pre-dried. During the drying process, the moisture content is reduced and the strips are then ready for the frying process. Caramelizing of crisps during frying implies that the sugar content in the potato remains too high. Thus, the blanching is not adequate. Thorough blanching with a steam water blancher is recommended. The recommended set of equipment for adequate blanching includes a hot water and steam blancher, an air knife, and a sweep to remove surface moisture. Alternatively, a blower or dryer that can remove surface water from the slices can easily be installed. The blancher will be able to significantly improve these factors. The processors also need to do basic testing of sugar levels in potatoes to determine the appropriate blanching time.
In a normal line of processing, the slices pass under air jets that remove excess water as they flow into 12.2 - 23m long troughs filled with oil. The oil temperature is kept at 176.6- 190.5°C. Paddles gently push the slices along. As the slices tumble, salt is sprinkled from receptacles positioned above the trough at the rate of about 0.79 kg of salt to each 45.4 kg of chips. Some manufacturers treat the potatoes with chemicals to improve the color of the final product. Potatoes are fried in either corn oil, cottonseed oil, or a blend of vegetable oils. Flake salt is preferred to crystal salt for the seasoning of the chips. Potato chips that are to be flavored pass through a drum filled with the desired powdered seasonings.
During frying the final texture and color is achieved. For coated fries and other potato products, a batter and pre-frying step is added before the normal frying system. After frying, the chips then pass through a defatting step before entering the freezer, on their way to the packaging system. However, the mechanical and manual frying often done by small scale processors, do not ensure uniform frying of the potatoes. The equipment is unable to maintain constant temperature during frying. Sometimes, the slices are fed manually into frying troughs with a wire mesh belt, which holds the potatoes during frying and pulls out at the other end after frying or the slices are fetched with huge ladles and placed in deep frying pans. The conveyer takes the slices from the fryer through a defatting process and onto the freezer. Often, however, the oil contains too much water, which increases the frying time. The absence of oil filters also reduces the life span of oil used by these. The removal of water from the surface of the potatoes is needed. As recommended earlier the addition of an air sweep to the blancher will solve this problem for the factories. Well fried crisps and chips are light colored with low fats. To achieve adequate frying, the recommended set of equipment includes a belt fryer, oil tank, heat exchanger, filter and boiler, heat recovery, a belt with a leaking tray for cooling and defatting. In addition to these, the processing of frozen chips may require a dryer. The batch or manual feed fryer is recommended for processors in Kenya given its cost and capacity, although the continuous line is most preferred.
After frying and removal of superficial fat, the product is cooled. In the case of frozen chips, they are deep-frozen within a short time (of about 20 minutes) in order to retain texture and to avoid damage because of ice crystal formation.
Medium scale processors mainly use a wire mesh belt that pulls out the hot chips from the end of the frying trough. As the chips move along the mesh conveyer belt, excess oil is drained off and the chips begin to cool. Sorting is conducted to pick out burnt slices. Small scale processors normally do this manually (with the hand).
Some processors do have a conveyer from the fryer through defatting to the freezer. The normal weight loss for frozen chips during freezing is 1% of the weight prior to freezing. The local Shangi variety turns grey after frying. This has been attributed to enzymes in the potato, which is not completely removed by blanching. This makes the Shangi variety unsuitable for processing. The ideal freezing equipment for frozen chips comprises pre-cooling, an IQF (Individually Quick Frozen) freezing tunnel, and refrigeration plant. The pre-cooling and defatting is often done with a fan to blow off fat and decrease the temperature. The IQF tunnel freezer is suitable for all sorts of vegetables and fruits. The challenge with this IQF tunnel freezer is that it is very expensive, particularly for small volumes. The minimum capacity is 1000 kg/hour and the maximum 7500 kg/hour. Therefore, it is not economical with a production of less than 800 tons per year. It can further be inefficient to operate if it is not used continuously. This is because the start-stop consumes energy and it needs cleaning once it is defrosted.
Packaging offers protection to the final products from contamination and allows the processor to provide information about the product as well as persuade users to patronize the product through branding. A usual packaging line consists of a weigh scale or a dispenser, a foil bag cutter, a filler, and a sealer. Packaging equipment is said to account for up to 50% of the costs of a crisps line. It is usually not purpose-made for chips or crisps and can be used for other snacks as well (i.e. nuts).
Crisps should be conveyed to a packaging machine with a scale. As the pre-set weight of chips is measured, a metal detector checks the chips once more for any foreign matter such as metal pieces that could have come with the potatoes or been picked up in the frying process. Other processors use smaller plastic bags (retail sizes) for packaging, and the chips are placed manually in the plastics and weighed. Two forms of packaging machines are available for crisps. The first is the vertical form, which fills and seals packages. The second one is the box form. The vertical form makes bags from rolls of plastic foil, automatically weighs the right amount of crisps per bag, fills the bags with crisps, and finally seals the bags. The box form is economical and mostly used in Africa. It is thus recommended for crisps lines. With this, the plastic foil is manually folded and taped (sealed) and the boxes are then filled with sachets manually.
Processors use plastic bags, but do bulk packaging in high volumes for storage first. In order to transport the frozen chips they are re-packed into plastic bags of different sizes for the different markets. Often at small scale processing companies, the required quality of the products can only be guaranteed for a few hours, so the production is done throughout the night and the products are delivered directly the next morning to the customers. Given that chips cannot be stored for a few days by the client or the producer and considering the throughput of these processors, a manual foot-operated bag sealer, a manual vacuum packer, nitrogen flusher, and a small cold storage would be a significant improvement for packaging and storage of the final products and to pack directly in retail packaging (not first in bulk) which will decrease the use of packaging material, and hence lower the costs.
Supermarkets and restaurants play a role in the distribution of potatoes, particularly processed potato products (frozen chips and crisps). Processors mostly supply their potato products directly to supermarkets and restaurants. Restaurants are a major outlet for the potatoes consumed in urban centres. Many of them specialize in chips (French fries). Restaurants use potatoes to make chips bhajia (spiced slices of potatoes) and mash-based dishes that use potato on its own or mixed with other ingredients.
In Kenya the processing industry accounts to 9% of the market at the moment, from which French fries is the most popular product (5%), followed by crisps and other snacks (3%) as well as starch, potato flour, and flakes (1%). The target customers for crisps are direct consumers. Crisps are a final product that can be purchased off the shelf and consumed directly by the final user. In contrast, chips mainly target restaurants, where they will be prepared for final consumption. The processing of fresh chips is very similar for frozen chips but significant differences exist in their target markets, entry barriers, and volume-margin ratios.
Fresh chips have low entry barriers, and restaurants do not need to invest in cold storage. Advantages of frozen chips are that restaurants do not need to par-fry (which saves labor, energy, and oil) and also don’t need to arrange daily deliveries as compared to fresh chips.