Traditional, Value-Added Applications of Dry Peas, Lentils & Chickpeas
Thanks to their robust nutritional profile, pleasant flavor, comparatively low cost, and cooking versatility, legumes have been an important part of the human diet for millennia. From the Fertile Crescent to the Palouse and over to the Northern Plains, USA dry peas, lentils, and chickpeas have provided an incredibly broad array of products and been incorporated into an endless variety of dishes.
As previously discussed, food legumes are a valuable source of dietary proteins and significant contributors to a healthy diet in many parts of the world. Foods based on legumes are prepared with a wide range of recipes and prepared with a host of different methods, including soaking, decortication, grinding, sprouting, fermentation, boiling, mashing, roasting, milling, parching, frying, and steaming.
Legumes go through several primary processes (e.g., dehulling, boiling, roasting, splitting, dehydrating, and grinding, etc.) before they are ready to be used in food preparations. For example, as was noted earlier, roasting or puffing of legumes by subjecting them to high temperatures for a short time has been practiced in Asia, the Middle East, and South America for many years.
One challenge with preparing pulses can be the length of time it takes to cook them. To expedite use, pulses are often processed first before being treated to additional cooking, frying, or roasting. Popular methods in the developed world include canning cooked pulses and incorporating them into what are referred to as ready-to-eat (RTE) products, such as chili.
Without access to such production options, producers in developing countries typically process pulses to be sold as shelf-stable products, requiring a minimum investment in packaging. Examples include low-moisture foods like baries, papads, leblebi, and others.
Throughout the world, food manufacturers use pulses as ingredients for products targeted at niche markets or to serve products that are unique within different cultures such as falafel, hummus, and dhal. Since the 1980s, technological advances in research and development in both products and machinery have led to a greater demand among food manufacturers for equipment that will enable them to boost capacity and enhance product quality.
Once a small industry, employing pulses as a base ingredient for a vast array of products is today an increasingly popular practice and offers myriad benefits for both food developers and consumers alike. The diversity of products that can be produced using pulses frees manufacturers to introduce ingredients from different legumes. This enables them to modify the taste and texture of the food item, while helping ensure that consumers enjoy a product that is unique, healthful, and easily distinguishable from traditional snack foods. See Appendix C for a collection of sample formulations.
Soup represents the most common use for food legumes. Manufacturers are always searching for new soup varieties because they understand that shoppers increasingly expect to be offered consumer-friendly options. They are learning that incorporating legumes won’t substantially raise the cost of goods, while offering a rich nutritional profile and making possible an ever-expanding variety of recipes.
Today, virtually every region in the Middle East seems to have its own signature lentil soup recipe. There is a Levantine lentil soup with silverbeet, an Armenian variety that uses lamb stock, a sour Cypriot version with vinegar, and an Arabian offering distinguished by spices, tomatoes, and lime.
In North Africa, lentils are joined with chickpeas and lamb for a popular stew called harira. Egyptians have koushari, a mix of lentils, noodles, and rice, a traditional Coptic meatless “fasting” dish.
As health- and heart-conscious consumers increasingly demand a healthy option, food developers have incorporated legumes into canned soup, frozen soup, shelf-stable mixes, “instant” dry soups and others. They can also be used as a soup thickener to add an affordable heartiness to existing soups.
Legume-based instant mixes offer an easy, practical way to create delicious and nutritious soups that are quick and simple to prepare.
Before legumes can be used in instant dry soup mixes, they must first be pregelatinized or precooked via one of several processes. The most common method involves soaking the pulses, boiling them, making a slurry of the boiled product, drying the slurry in a drum drier, and milling the result to make flakes or powder.
For the best results, food developers should have the final product in mind when selecting the soup ingredients. The following considerations should go into determining which pulses and ingredients to use:Performance—Preparation method, rehydration time, further processing, and holding time are important considerations. Pregelatinized powders are best for instant soups, precooked powders for simmer soups, and pulse ours for soups requiring longer cooking times.
Target appearance—Key to choosing the right ingredients is determining the desired appearance and integrity of the final product. Pulses are available as whole, pieces, flakes, or our, each of which will impact the final product.
Performance limiting or enhancing ingredients—Other ingredients like rice, pasta, dehydrated vegetables, seasonings, and thickening agents must be accounted for as they can affect results (e.g., water absorption).
Practical & NutritiousA great variety of soup formulations can be developed using pulses. Not only practical for today’s busy lifestyles, such products also align with the trend toward healthy diets and nutritious alternatives. Given the right flavor, ingredients, and packaging, legume-based soup products can be the perfect choice for today’s consumer, suitable for any meal and any time of year.
Recent reports indicate that the eating habits of the average adult consumer in the U.S. have markedly changed in the last decade. As a consequence of lengthening commute times to work and increasingly irregular work hours, consumers have adopted a more on-the-go approach to meals. This has driven many Americans to fast-food restaurants and store-made, precooked meals.
The result, according to many health care professionals, has been a steady increase in the rates of obesity, diabetes, and heart disease, among other issues. As the media focuses on such issues, consumers are responding. In market research conducted by Tate & Lyle, a leading manufacturer of renewable food and industrial ingredients, 65 percent of consumers are trying to eat healthier, though some 33 percent concede that they don’t have the time to prepare or eat healthy meals.
As general market attitudes turn away from traditional salty or fatty-type snacks to healthier, trans-fat-free options, the global volume of international snack foods is expected to continue to increase to meet these demands. Though the U.S. remains the largest single market for such foods, Latin America, Asia Pacific, and Eastern Europe represent the greatest opportunities for manufacturers of snack foods.
With a long history as healthy, nutritionally rich ingredients dating back thousands of years, pulses continue to play an important role in providing consumers with healthy snack food options. Such foods are traditionally prepared by first being cooked and then roasted or fried. The following section explores how this is done.
Subjecting legumes to heat for varying periods of time (i.e., toasting and roasting) is widely practiced as a method of food processing. Roasting legumes by subjecting them to high temperatures for a short time has been practiced in Asia, the Middle East, and South America for many years.
The roasting process stabilizes pea flour, partially gelatinizing the starch, denaturing the protein, and inactivating enzymes to increase product shelf life. Roasted pea flour serves as an effective flavor carrier and flavor improver, ideal for making more nutritious flatbreads, tortillas, pita breads, crackers, cookies, energy bars, and extruded snacks. It also enhances dough yield, firmness, and texture.
The roasted chickpea, called leblebi, is widely enjoyed as a traditional snack food in Turkey, the Mediterranean region, and the Middle East, though the method of preparation can differ from country to country. Roasted chickpeas can also be found in the US. Pacific Horizon packs and distributes the Mi Familia brand of roasted chickpeas with spicy chile and lime flavor coating and can be found in grocers along the West Coast.
In general, leblebi production begins when chickpeas are subjected to heat treatment in several stages after which water is added to increase the moisture content. They are then allowed to rest for several hours before being roasted.
Large-seeded chickpeas are preferred for leblebi. Today, there is no large-scale industrial production of the snack. It is generally produced using traditional methods by small-scale manufacturers.
Materials & Methods
Cleaned chickpeas are graded according to size and subjected to heat in several stages. Studies of raw and roasted chickpeas have revealed that substantial structural changes occur during processing. The raw chickpea is tightly packed and contains no air pockets. A large number of air pockets are, however, formed in the cotyledon of the roasted chickpea.
This change is believed to be the result of the chemical and physical changes that the chickpea undergoes during processing. As noted, after the heat treatment, water is added to increase the moisture content of the chickpeas.
During the roasting process, this water changes from a liquid into vapor inside the chickpea. The chickpea expands, likely the result of the steam generated from the water vapor that then pushes on the compact structure of the chickpea.
Because the majority of the starch granules do not gelatinize during roasting, researchers consider the amount of water as a major factor in swelling and gelatinization.
A study conducted on roasting lentils demonstrated that temperatures as high as 257 degrees F (125 degrees C) were attained in the lentils during processing.
This enables the superheated steam to create voids in the cellular matrix. At the later stages of roasting, the steam exits and the starchy matrix is dehydrated, causing a porous and slightly extruded-like structure.
Raw and roasted chickpeas also differ significantly in color. Roasted chickpeas have a darker color with more yellow and red than raw chickpeas. These changes in color are probably indicative of chemical browning reactions during roasting.
Color is an important consideration in food products as the color and appearance of foods are generally the first impressions consumers have of a specific product. The darker color of roasted chickpeas is generally preferable to that of raw chickpeas.
More Innovation to Come
Legumes are a key piece of a healthy diet as identified in the 2005 USDA food pyramid and highly lauded Mediterranean Diet. Ethnic foods like leblebi have the potential to help consumers more successfully incorporate legumes into their meals. Ongoing research into new and more effective ways to process and prepare these foods is, therefore, a key tool in learning how to continually expand the number of products into which legumes can be successfully added.
Different varieties of pulses can be fried in oil to manufacture a range of alternative snack products. It is essential that manufacturers not only have the right equipment to do this properly and safely, but also the technical know-how to produce the highest quality product with that equipment. The processes and supporting technology involved in frying pulses is also critical, whether you’re producing fried peas, fried chickpeas, or fried lentils.
Fried Green Peas
Fried peas can be eaten as a snack or consumed as part of a mix of snack food products. The characteristics of a pea perform differently during frying than most other pulses. To fry a pea, therefore, requires a very different process than frying a typical pulse.
The process begins with choosing the appropriate pea variety. It is important that the chosen pea produce the texture sought by the customer. Once dehydrated it may boast a smooth skin, but that does not necessarily mean it is suitable for producing fried peas.
The pea is soaked in sodium bicarbonate. The peas are rehydrated in water that is held at room temperature for approximately eight hours. The soak time is critical. Peas soaked for longer than nine hours tend to produce a higher level of fines (i.e., small legume pieces freed during processing) as their skins are removed more easily during the cooking process. Oversoaking will also lead to pea fermentation, rendering them unusable by the manufacturer. Product quality can also be seriously compromised if the peas are allowed to rupture.
Temperature during soaking is important. Too high a temperature will cause the starch within the peas to gelatinize and the protein to denature (i.e., to diminish or eliminate some of its original properties, especially its biological activity).
During the soaking step, the moisture content of the peas increases up to 57 percent, while expanding the peas to approximately twice their original size. Peas soaked in sodium bicarbonate also have a lower bulk density.
One of the main reasons for using sodium bicarbonate is to trigger a reaction with the acid in the pea. A hydrogen ion from the pea that reacts with a bicarbonate ion, carbon dioxide is then released, thus expanding the peas.
Changes in Coloration During Soaking
Adding the sodium bicarbonate has a demonstrable effect on the color of peas as well. By initially increasing the pH of the soak water (sodium bicarbonate is a mild alkali), it reacts with the chlorophyll to enhance the pigments within the pea. The phytyl and methyl groups are displaced and bright-green water-soluble chlorophyllin is formed. The sodium salts of chlorophyllin give the soaked peas their bright-green coloration. Even greater brightness is achieved with the addition of green food coloring in the soak water.
Increasing the pH of the water ensures that the water absorbed into the pea will have a higher pH than the pea contained when de-hydrated. In this way, it also alters the normally intense blue coloration of the dried pea.
Once the peas have been soaked, they must be fried to reduce the moisture content below 2.5 percent. A fryer designed specifically for frying green peas is preferred. Ideally it should include a single frying pan that holds oil and controls the temperature pro le of the oil throughout the fryer. The flexibility to vary the temperature of the frying oil can help improve the product quality of the peas. The quality tends to be better when employing a frying system that uses a lower temperature at the start of the frying process and a higher temperature near the end.
Peas are sensitive to high temperatures. Using a fryer that can control the temperature pro le is, therefore, crucial to maximizing quality. Toward that end, considerable attention is paid to the rate at which the fryer temperature increases as this is necessary to ensure that the final moisture content is acceptable. A temperature increase that is too slow will result in a final moisture content that is too high.
This temperature pro le produces no surface blistering and less expansion of the pea skin. Peas placed directly into oil at 356 degrees F (180 degrees C) experience surface blistering and greater expansion of the skin surrounding the peas.
Submerging the peas at too high a temperature in the critical early part of the process causes the skin to be dislodged and the cotyledon to be expelled into the oil. Too low a temperature will lower the output, lengthen the fry time, and increase the oil absorption. The best products are those produced via a frying system that is able to leverage both quality and throughput.
The sodium bicarbonate also performs a critical function during frying by softening the texture with the production of carbon dioxide that occurs at temperatures over 248 degrees F (120 degrees C). When the peas are fried, a lighter texture and a better mouthfeel are produced.
Changes in Coloration During Frying
The bright-green coloration of the pea developed during soaking will change during frying. This occurs because when the peas are placed in the fryer at elevated temperatures, their cells are disrupted. The contents of their cells (including organic acids) escape from the vacuoles (i.e., a membrane-bound cavity within a cell) into the cell and into the oil.
As the acids contact the chlorophylls they change in such a way that the yellow and orange pigments within the peas are made visible along with the intense green chlorophyll. This combination gives peas an olive-green appearance, a color they will retain even after being fried, unless artificial green coloring not added to the soak water.
Oil Deterioration During Frying
Managing and minimizing oil deterioration is an important part of promoting the highest quality fried pulses. A number of different elements contribute to the deterioration of the frying oil, including UV light, certain metals (e.g., copper), water, and oxygen. These catalysts should, therefore, have limited contact with the oil.
For a product like fried peas, it is fairly difficult to minimize the contact with water as it is necessary to remove a large quantity of the water present in the peas during the frying process. A good filtration system and the correct frying parameters will help minimize deterioration.
The life of the oil can be further extended by keeping the level of fines to a minimum during frying; this practice also promotes a better yield and higher quality. Those fines that find their way into the frying oil will remain unless filtered out or removed via a sludge removal conveyer. If they are allowed to accumulate it will cause hydrolysis (i.e., chemical decomposition brought on by reacting with water) of the oil.
The oil can be protected if the processor is able to adjust the temperature pro le during the frying process. This helps minimize the level of fines produced from ruptured cotyledons or skins being removed from the peas.
Design Features of the Fryer
Continuous frying systems are equipped with a hood, which prevents oxygen from coming in contact with the oil. Such systems also include a damper on the flue (located on the hood) to modulate the level of steam above the oil. Frying oil left open to the atmosphere without a cover will oxidize more quickly. Because oxygen has a lower solubility in oil at a higher temperature, there is less susceptibility for oil oxidation at higher temperatures.
The fryer hood also captures the steam released as the product is frying, while the damper modulates the amount of steam that is released from the hood. With the damper open, more steam is released from above the fryer, helping protect the oil from oxygen and thereby minimizing oxidation.
Fried Lentils Soaking
Lentils are first soaked for three hours in water that is held at room temperature for a final moisture content of about 50 percent. As with chickpeas, lentils are then rinsed and drained to remove excess water.
When fried, lentils perform differently than green peas or chickpeas. Because lentils are not as susceptible to thermal shock when initially placed in the fryer, a single temperature zone is permissible. A temperature of 356 degrees F (180 degrees C) is used to quickly decrease the moisture content in the lentils. Thanks to the lentils’ large surface area and the rapid heat transfer into the product, the required frying time tends to be very short.
The large surface area (when compared to the lentil’s total size) also leads to there being a lot of oil that remains on the surface of the lentil. If not removed, this oil will be absorbed as the product cools, increasing the total oil percentage of the product.
Subjecting the lentils to a centrifuge is perhaps the most common means for removing the oil. As it reduces the final oil content in the product, the centrifuge also allows the surface oil to be recirculated back into the fryer. The final moisture content required is 1 percent to 2 percent with an oil content of 20 percent to 30 percent.
Due to their high protein and low fat content, fried chickpeas are sold as a healthy alternative to other snack foods. To obtain the desired texture in a fried product, the variety of chickpea must be considered. The two principal varieties used to produce fried products are the Kabuli and the Desi, with the preference largely a product of the manufacturer and the costs of the raw material.
The Kabuli, which is more rounded than the Desi, offers a less wrinkled surface and generally requires less time to cook than the Desi. It also contains a seed coat that is very thin, but adheres well to the cotyledons.
Chickpeas are soaked for approximately 10 hours in water that is held at room temperature. Soaking increases the moisture content to approximately 53 percent. After soaking, the chickpeas are rinsed and drained to remove any excess surface moisture.
Chickpeas have an anatomy similar to the green pea and therefore have some of the same challenges during frying. It is necessary, for example, to ensure that the fryer can vary the initial and final frying temperature. Otherwise, the oil has to be set at a low temperature. If the temperature is too high there can be rupturing of the skin and an increased level of fines.
If the temperature is too low, product output will be reduced and more oil absorbed. Allowing the temperature to slowly increase during frying recognizes the vulnerability of the peas to higher temperatures and helps promote increased output while minimizing oil absorption.
A Focus on Leblebi
Roasted chickpeas, called leblebi (leb-leb-ee), a word that originated from the Persian word leblebû, have been a popular traditional snack food in Turkey, the Mediterranean region, and the Middle East for generations. It also has a growing popularity in North Africa, the Middle East, Europe, and Asia.
A significant amount of leblebi is still produced in Turkey and exported. Some Middle Eastern countries also produce small amounts, but there is today no large-scale industrial production. Roasted chick-peas are typically produced by traditional means at small-scale family plants, the methods having been handed down from father to son.
Leblebi boasts potential as a healthy snack and a natural ‘‘functional food’’ due to its chemical composition: It is high in protein, cellulose, and mineral content, and low in fat and calories. It has a soft, crushable texture, a special roasted flavor, and a sweetish taste. Product diversity can be expanded by covering leblebi during the roasting stage with salt, sugar, chocolate, or spices such as red hot pepper, ginger, cloves, and other edible coatings.
Thanks to its low moisture content, leblebi also has a long shelf life, safely storable for six to 12 months, depending on the packaging.
Quality Criteria for Leblebi Chickpeas
Quality criteria like shape, size, color, and harvesting time all vary depending on the cultivar, helping determine which chickpeas are used for leblebi. Preferred are the large-seeded, lighter-colored, round, smooth Kabuli type. The chickpea must also have a thick seed coat and the hull must be easy to remove during processing.
Harvesting time plays an important role in the tempering process of chickpeas as well as in the quality of the final product. Classification by size is an important stage of leblebi processing as is cleaning them of foreign material and any undeveloped, damaged, shrunken, or broken seeds.
There are three types of heating equipment used in leblebi processing:
- The cylindrical drum roaster (CDR)
- Roaster and hull remover (RHR)
- Roaster and speckler (RS)
- Liquid petroleum gas (LPG) is used for heating the CDR. This equipment may also be used for tempering chickpeas.
The RHR has a heating pan made of copper or iron. A copper pan is typically preferred due to its higher thermal conductivity. The inside surface of the heating pan is roughened and nicked to increase total roasting area and facilitate removal of the hulls. LPG is used for heating the pan and a gas input meter is used to control heating. The RHR has a paddle made of poplar wood that rotates while pressing the chickpea seeds.
The RHR heating pan usually ranges in temperature from 176 degrees F to 266 degrees F (80 degrees C to 130 degrees C). The main features of the roaster and speckler (RS) are a stainless steel heating pan of about 20 inches (50 cm) diameter, which operates as a heating device, and a motor adapted to a set of specially designed pulleys. The RS also has a paddle made of wood or rubber for mixing the chickpeas. The temperature of the roasting pan is around 212 degrees F to 266 degrees F (100 degrees C to 130 degrees C).
The Processing Steps for Leblebi Production
Step 1: Cleaning and Grading
The grading stage is key as the size of the chickpea impacts the tempering (heating and resting) and roasting treatments during processing. The chickpeas are first cleaned of all foreign material and any undeveloped, damaged, shrunken, or broken kernels. The cleaned chickpeas are then graded according to their seed size. This is done using separators, which are usually comprised of five sieves varying in dimension from 6 to 10 mm. Chickpea fractions greater than the size of each sieve are used separately for leblebi production, while seeds greater than the 10 mm fraction have potentially high leblebi quality.
Step 2: Soaking
The most serious shortcoming when it comes to using legumes is their long cooking time, making soaking an important precooking step. Usually done overnight, soaking reduces the time necessary for tenderizing the texture of the chickpea. Several studies have reported the beneficial effects of soaking in salt before cooking or using various salt solutions in the cooking of pulses.
Step 3: Tempering (Preheating and Resting)
Tempering in leblebi production means holding the seed (resting) after heating to allow moisture penetration and stabilization. The chickpeas are heated for five minutes to eight minutes at around 212 degrees F (100 degrees C) before resting in a food-grade approved container for 12 to 18 hours and up to two days. The chickpeas are then spread on a cooling bed platform for slow cooling. A moistening step is often included as well.
Step 4: Resting
Resting is among the most important steps of leblebi production as many of the changes that take place in roasted chickpea kernels occur during this process. During certain kinds of leblebi processing, the volume of the roasted chickpea kernels increases and swells, while their hulls start to separate from the cotyledons.
Step 5: Boiling
Pulse seeds are cooked to help produce a tender edible product and develop aroma. Traditionally, dry or soaked seeds are cooked in boiling water in an open pan for one to two hours or for 10 to 15 minutes under pressure.
Step 6: Roasting
The roasting, or parching, method usually involves whole seed, non-dehulled grains being exposed to dry heat. The traditional Turkish household practice includes first sprinkling the pulses with a little water and then mixing them with preheated sand or preheated edible salt in a roasting pan. The pan is kept on an open fire and maintained at a temperature of 392 degree F to 482 degrees F (200 degrees C to 250 degrees C), depending on the pulse variety. The roasted pulses are then separated from the sand (or edible salt) by sieving.
Step 7: De-hulling
The de-hulling step usually includes two parts: loosening the hull by dry or wet methods and removing the hull and cleaning. Loosening the hull can be achieved by any of the following techniques or a combination:
- Drying in the sun until the hull is loosened
- Applying small quantities of edible oil, followed by several hours or days of sun drying and tempering
- Soaking in water for several hours, followed by coating with red-earth slurry and sun drying
- Soaking in water for several hours to loosen the hull before manufacture of food products
- Once the de-hulled whole cotyledons are separated, the process is repeated until as many of the pulses are de-hulled as possible. Such repetition can, however, cause splitting and breakage of the pulses.
- Chemical, Physical, and Structural Changes
During leblebi processing, carbohydrates and proteins are modified as a consequence of the heat treatment, including the carmelization of polysaccharides on the surface of the chickpeas. In addition, some acids are partially decomposed during roasting, while volatile acids are partially lost due to evaporation. Chickpea volume increases during processing at the same time the density and kernel weight decrease. The flavor can also change, especially as a result of the heating processes.
During the resting stage other changes can occur, some positive (e.g., ripening) and some negative (e.g., off flavor). The original raw chickpea is dense and contains no air spaces. But during roasting, the water inside the chickpea changes from liquid to vapor, which, given the compact structure of chickpeas, can cause an increase in the vapor pressure of water so that the steam that is generated triggers expansion during roasting.
This can lead to development of a large number of air spaces in the cotyledons and give roasted chickpeas a porous structure and an opaque, chalky appearance.
Canning and freezing processes vary according to variety, pea size, and period of maturation. Two distinctly different types of canned peas are manufactured: canned fresh peas and canned processed dry peas.
The former are produced exclusively from peas harvested at an early stage of maturity. These peas, called vining peas, are extremely perishable. They must be processed in the cannery within a few hours from the time of harvesting to retain their excellent sensory properties and prevent preprocess microbial spoilage.
Canned processed peas, on the other hand, are manufactured using dry peas that have been allowed to mature fully in the field before harvesting. In the dry state, these peas are perfectly stable and may be held for long periods until canning.
Manufacturers of canned processed peas enjoy certain production advantages not available to those producing canned fresh peas. The stability of dry peas, for example, permits manufacturers to can peas throughout the year. Doubling their weight during processing, dry peas, typically of the round-seeded green variety if grown in the U.S., also offer a comparatively inexpensive raw source of protein and dietary fiber, in addition to being full of flavor.
The Manufacture of Canned Processed Peas
The manufacturing process for canned processed peas is similar to that used for fresh peas, with the exception that a pre-soaking operation is used to rehydrate the dry peas prior to blanching.
USA Dry Round-Seeded Green Peas
To help ensure consistent, acceptable quality, the choice of supplier and the specification of raw materials are of paramount importance. USA dry green peas are the round-seeded, fully mature peas. They are cleaned and sorted in accordance with specified USDA grades (USDA No. 1 grade peas are recommended for canned processed peas).
The raw materials should be clean and free of foreign material (e.g., stones, metal, dirt, etc.) or extraneous vegetable material (e.g., weeds, berries, or leaf and stalk pieces). The peas should be whole and unbroken, and without stain, blemish, or insect damage. These factors, along with many others, are described in the USDA grade specifications for dry peas. The moisture content is also important because this will affect both the storage of the peas and the rehydration behavior during the canning process. If artificial drying of the peas is necessary, it must be conducted very carefully or the quality of the peas can be compromised.
Once harvested, dry peas are delivered into initial processing at about 10 percent to 13 percent moisture. During storage prior to canning, the moisture content can rise to 14 percent, depending upon storage conditions, before storage performance is significantly affected. Conversely, peas with excessively low moisture may show poor rehydration behavior during the soaking process.
Typical Processor Specifications
The USDA grading system is used for peas with a variety of intended uses. For the successful manufacture of canned processed peas, the following specifications are typical of those used by commercial canners. Dry peas of the green varietal type should meet the following criteria:
- Bleached peas <10 percent unless individually agreed with specific consignment
- Total amount of peas of contrasting classes <0.3 percent; amount of such peas that turn black on canning <0.02 percent
- Shriveled peas <2.0 percent
- Amount of peas showing visible cracks in seed coat <3.0 percent
- Amount of split peas <0.5 percent Amount of damaged peas <1.0 percent
- Amount of weevil damaged peas<3.0 percent
- Amount of defective peas <4.0 percent Ÿ Amount of foreign matter <0. 1 percent Ÿ Free of live weevils
- Number of peas containing dead mature weevil: not more than one pea in a sample of 20 pounds
- Moisture content <14 percent by drying at 221 degrees F (105 degrees C)
Sugar is used in the brine covering for canned processed peas. It should be of food-grade quality. Canner’s grade sugar may also be an option as it has a guaranteed low count of thermophilic microorganisms. (There is an International CODEX Standard for white sugar, CODEX STAN 4-1981, which details quality factors and permissible levels of contaminants.)
Salt is also used in the manufacture of brine, and like the sugar, it should be of food-grade quality. (There is an International CODEX standard for food-grade salt as well, CODEX STAN 150-1985.)
Synthetic and natural coloring choices are important in the production process as well. Blue and yellow are common as a means for producing the appropriate green color; dyestuff companies generally provide a pre-blended mixture to meet individual requirements. As natural colors invariably do not have the heat stability to provide a suitable green color within the finished product, synthetic dyestuffs are preferred. Most countries have legislation controlling such colors.
Water for the Brine
Water used in the brine should be of potable quality as both chemical and microbial contamination are important considerations. Also, the water in the distribution system within the factory should conform with requirements.
In practice, it is important that limits are established for the water in the plant and that any significant variation should be investigated immediately. The hardness of water used in the canning of dry peas is a determining factor in product texture. Softened water (65 ppm to 155 ppm calcium carbonate) is generally used for initial soaking, whereas the normal factory water supply is acceptable for the brine.
Preparation of Dry Peas for Canning
Dry peas purchased in the U.S. have already been cleaned and sorted prior to being sent out. It is nevertheless recommended to include the following items as part of the manufacturing process:
- A form of riffle plate—for stone removal
- A magnet or metal detector—for the removal of metallic debris
- A sorting belt—to observe the quality of peas immediately before filling and to allow the manual removal of any unwanted material
Dry peas are soaked for 15 to 24 hours in tanks constructed from stainless or galvanized steel or a suitable plastic material. During the soaking period, the peas swell and absorb enough water to account for 95 percent to 110 percent of the dry pea weight. The water temperature is ideally less than 68 degrees F (20 degrees C).
Since wet peas are an excellent medium for microbial growth, warm weather often makes it necessary to change the water once or twice to prevent a souring of the peas.
The peas increase in volume as they absorb water and it is important that they continue to be covered with water for soaking. Note that the soaking tanks should not be so large that the peas at the bottom are compressed and prevented from swelling. About four tons is the maximum recommended tank size.
Hardness of Soaking Water
Excessive calcium levels in the soaking water may cause changes within the pea structure, resulting in excessive hardness of texture. To avoid this, it can be necessary to adjust the calcium carbonate level to 65 ppm to 155 ppm.
Water that is too soft can cause splitting of the peas and mushiness within the can. If a source of soft water is available, it can be mixed with hard water to obtain the desired balance. It is also important to remember that although the majority of water absorption takes place during the soaking process, it does continue to a lesser extent during blanching and sterilization.
After the pre-soaking operation, peas are normally drained and then transported in a flume of water, across a riffle plate to remove stones, then continue to the blancher. It is important to get the direction of the riffles correct, and their precise angle must account for the rate of water ow to achieve maximum effectiveness.
Blanching is an important operation within the manufacture of processed peas, accomplishing the following:
- Cleaning of the peas
- Reduction in microbial count on the peas
- Destruction of enzymes that can promote chemical deterioration of the peas
- Additional soak-up of water prior to
The blancher typically comprises a large steel vessel partially filled with hot water. Peas enter at one end and are contained behind a perforated screen running the length of the vessel. They are sent to the outlet end by a rotating helical screw, at a speed which the screw moves to control the blanching time.
Also important is control of the water temperature as too low a temperature can lead to the growth of thermophilic microorganisms and give rise to souring. Typical blanching conditions would subject the peas to water at a temperature of 190 degrees to 199 degrees F (88 degrees to 93 degrees C) for four to six minutes.Though usually unnecessary, blanching water, as with the soak water, may be partially softened to 65 ppm to 155 ppm calcium carbonate.
The can and the can end are critical components in the manufacture of canned food that retains product quality during prolonged storage and safety for the consumer. It is essential, therefore, that only reputable can suppliers are used who provide cans of suitable specification and also adequate technical support in case of difficulty.
After unpacking or depalletizing, empty cans should be inverted and internally sprayed with steam or water before entering the filling machine.
Peas are filled through an adjustable volumetric filler before the addition of brine. National standards and legislation must be consulted with regard to the required fill weight for peas. In many cases, the basis for trade of canned goods is dependent upon drained weights measurable at the time of consumption.
Brine Preparation and Filling
Brine is prepared by dissolving the required ingredients in water in an appropriate, preferably stainless steel, steam-jacketed pan. The temperature should be raised to 203 degrees F (95 degrees C) before the prepared brine is distributed to the filling line. Filling temperature should ideally be above 185 degrees F (85 degrees C).
The holding time of the brine before filling should not exceed 45 minutes or color degradation will result. Brine is generally filled into the cans until the cans are over owing with brine. This is achieved with the use of a perforated pipe or a series of nozzles under which the cans pass. After filling with brine, the can is tilted to provide a specified headspace before double seaming. The headspace and filling temperature should be sufficient to produce an internal vacuum within the can. The overflowed brine is screened and recirculated.
Failure to correctly form a double seam can lead to spoilage and either a food poisoning incident, commercial loss, or both. Two important considerations in this step include:
- The can supplier should provide details of the double-seam specification, which should then be adhered to.
- The specification should include acceptable measurements for both seam tightness and the overlap of the end and body hooks.
Cans of peas are packed into crates, which are placed inside a suitable pressure-sterilized retort (i.e., a sterilizer of food cans). Sterilization is a crucial step. For all low-acid foods (pH >4.5), it is essential that a thermal process is used that is sufficient to achieve commercial sterility (i.e., destruction of all pathogens and all other micro-organisms capable of metabolism at the intended product storage temperature).
All commercial processes should be validated by heat penetration tests. Also, if it becomes necessary to reprocess a batch of cans due to steam failure or some other reason, the original process times may no longer be sufficient as the material viscosity within the cans will have markedly changed.
After sterilization has been achieved, cooling water is introduced into the retort so that the cans are cooled as rapidly as possible, thereby preventing undue product degradation. Because it is vital that the cooling water is of good microbiological quality, it is normal that the water should be disinfected by the addition of chlorine gas or another suitable chlorine compound.
Immediately after water cooling, the temperature of the cans and their contents should be 104 degrees to 122 degrees F (40 degrees to 50 degrees C). The temperature should be cool enough to inhibit the growth of any surviving thermophilic organisms but warm enough for the cans to dry. Once the crates of cans are removed from the retort, they should be tipped—while still wet—to remove water from the can end.
Under no conditions should wet cans be manually handled due to a heightened risk of infection.
Good Manufacturing Practice in Canning
Good manufacturing practice (GMP) involves the application of the best available knowledge to ensure that food products are safe for the consumer, conform with their intended end-product specifications, and are produced in an efficient manner. Failure to apply GMP in the production and distribution of low-acid canned foods (i.e., those with pH >4.5) may lead to incidents of food poisoning, commercial spoilage, or both. The ultimate financial cost to the manufacturer can be significant.
Facets of GMP include the following:
- Support and understanding of the senior management of the company of technical issues, and an appropriate executive structure to ensure that policies and procedures are properly implemented Suitable premises, particularly in providing separation of pre and post-sterilization areas
- Adequate water supply, providing water for product make-up, can cooling, and cleaning
- A competent and reliable supplier of raw materials
- A competent and reliable supplier of cans and ends
- Suitable equipment for forming double seams and means for their evaluation
- Adequate understanding of the critical factors affecting the thermal processes for the products manufactured
- Validated sterilization processes, with supporting documentation
- Venting schedule, supported by temperature distribution data
- Suitable sterilization equipment fitted with adequate control and recording instrumentation
- Chlorinated water supply for cooling
- Suitable post-process handling procedures
- Means for product identification and traceability
- Plan for product recall (should this become necessary)
- Clearly defined authorities for product release
- Quarantine procedures
- Emergency procedures
- Documented process records
- Adequately trained staff, with documented training records
- The Technical Objectives of the Canning Process
The ultimate objective of the canning process is to provide safe, wholesome food to the consumer at an affordable price. Producers seek to achieve this goal by:
- Placing prepared food within a container
- Closing the container with an hermetic seal
- Supplying heat under controlled conditions to achieve commercial sterility
- Preventing post-sterilization infection
- Quality Systems Management
The production management team is responsible for providing an effective system with adequate resources for ensuring the safe production of canned foods. A fully documented quality system should be created in which the authorities and responsibilities are defined for all of the critical aspects of the canning operation, including:
- Raw material and container acquisition
- Product preparation
- Double-seamer operation and double-seam assessment
- Thermal process scheduling and validation
- Sterilization operations
- Product release and product recall
The team is also responsible for providing a system of audit and review to ensure that sound manufacturing practices are fully implemented and operating as intended.
Premises should be sited with due regard for the operations that are to take place within them. Construction materials should be conducive to good sanitation and suitable for the intended type of food processing. In particular, the site should:
- Be undertaken throughout production to root
- Provide adequate working space for the various operations performed.
- Prevent confusion or contamination between unsterilized and sterilized material.
- Offer production lines that are easily accessible from all sides to permit inspection, maintenance, and cleaning of equipment.
- Water Supply
The canning process requires considerable quantities of water for product make-up, can cooling, factory cleaning, and personal hygiene. Water may be provided from a town supply or from private sources, but in either case, it is necessary that data is established with regard to the microbiological condition of the water. Additional disinfection may be necessary if the water is to be used for can cooling.
Raw Material Supplier
Consistency of raw material supply is essential if the canner is to produce goods of uniform quality. Apart from the immediate aspects of sensory quality, it is also important that the raw material is clean and does not contain foreign matter.
Also, in the case of dry peas, the soak-up behavior must be predictable. Excessive water up-take during canning could lead to pea disintegration, which could adversely impact the effectiveness of the sterilizing process. U.S. peas must comply with a specification that can then be used by the canner for quality assurance of raw material.
Canning Elements: Cans, Can Ends, and Seams
Cans and ends represent critical elements in the safe production of stable, long-shelflife foods. Failure of the container integrity at any point may lead to microbial growth and product spoilage. Cans and ends should, therefore, only be purchased from reputable suppliers able to provide competent technical support with regard to the use of their containers. It is important that the can specification is compatible with the product and its intended shelf-life.
The can maker also has the primary responsibility for specifying the correct tolerances for can seam dimensions. Cans should never be used for other purposes than intended.
The correct formation of double seams requires suitable can and can end components as well as properly maintained and adjusted double-seaming equipment. Specially trained personnel should be responsible both for setting the double-seaming machines and for subsequent evaluation of the seams. Examination of double seams for visual defects should be undertaken throughout production to root out deficiencies.
Samples from each seaming head should undergo detailed examination at regular intervals, including before production begins, after a significant stoppage, or after adjustments are made to the seaming equipment. All pertinent observations and actions should be recorded. The frequency of sampling will depend on individual circumstances but should not normally exceed four hours.
Critical Factors Affecting the Thermal Process
Canned processed peas are a low-acid food (i.e., pH is above 4.5), which means it will support the growth of the most heat-resistant pathogen, (Clostridium botulinum). Therefore, it is necessary that the product is made commercially sterile by the application of an adequate heat process at a specified temperature, generally in the range 239 degrees to 257 degrees (115 degrees to 125 degrees C), within a pressure retort.
The effectiveness of the thermal process in consistently achieving commercial sterility—and consumer safety—in every can processed depends upon a number of critical factors. In the manufacture of canned processed peas, the following should be included within the scheduled process specification:
- Dry pea grade and size
- Soak-up ratio of the peas prior to filling Container size and shape
- Pea fill weight
- Brine fill weight
- Head space within container
- Brine filling temperature
- Stacking pattern for containers within the retort
- Minimum initial temperature prior to sterilization
- Venting procedure (for steam retorts)
- Process time
- Process (sterilizing) temperature
- Maximum product temperature after water cooling
- Product pH
An exact knowledge of the time-temperature history of the slowest heating part of the food within the can during the sterilizing cycle is used to determine the sufficiency of the sterilization. Each temperature may be ascribed a lethal rate with respect to microorganisms.
It is also necessary that a company is able to justify to its customers or to public health officials the thermal processes that are scheduled. Heat penetration records, in which the temperatures within a can are logged against time, are used to validate the thermal processes, and such records should be available for each product/container combination.
In retorts that sterilize foods using saturated steam, the relationship between pressure and temperature is defined (i.e., if temperature is specified, then pressure is also fixed). If air is present within the steam at a given pressure, a reduction in temperature will inevitably occur. For this reason, it is vital that in the operation of steam retorts that all air originally present in the vessel is purged from the system through adequate venting.
It is essential when manufacturing canned foods to use sterilizing equipment that is capable of consistent and controlled operation within defined parameters for temperature, pressure, and time. The pressure vessel must also comply with safety legislation. The requirements for a static batch retorting system are:
- Pressure vessel, generally with safe working pressure
- Means for locating containers within the retort in a controlled manner
- Heat transfer medium, either saturated steam or superheated water
- Means for venting of steam retorts
- Instrumentation, control and recording equipment
Traditionally, retorts have used saturated steam as the heat transfer medium, which imparts heat to the cans. Many such systems are in use today. Increasingly, however, superheated water retorts, either full immersion, spray, or shower systems, are being used. The principal advantage is that temperature and pressure can be independently regulated.
Retorts should be maintained in good condition and should be operated by suitably trained personnel according to documented factory procedures. Actions taken by the retort operator during sterilization should be fully recorded on a log sheet. This log should then be reviewed before the product is released.
Chlorinated Water Supply for Cooling
The primary requirement for container cooling water is that it should be free from microorganisms, which can gain access to the cans during the cooling process. Coliforms (i.e., any of several bacilli) should not be detected in any sample.
It is normal for chlorination to be used as a means for ensuring the suitability of cooling water. Chlorine gas or chlorine solution that may be injected into the water though calcium or sodium hypochlorite solution may be more convenient. Note, however, that excessive chlorine levels are extremely corrosive to cans and the retorts.
The major cause of spoilage in canned foods is post-process infection in which microorganisms enter through an imperfection in the can or double seam after sterilization. The factors below are commonly the cause of spoilage:
- A source of infection, which typically originates with a human hand
- Water that provides mobility for microorganisms
- A seam or can defect through which microorganisms can enter
To control infection, it is necessary to ensure that:
- Wet containers are not manually handled.
- Containers are dried as quickly as possible.
- Conveying and handling surfaces are routinely cleaned and disinfected to reduce microbial contamination.
- Conveying and handling equipment is designed, installed, operated, and maintained so as to cause minimum physical abuse to the containers.
Post-sterilization can cleaning is regarded as a hazardous operation and will always carry some risk of post-process contamination. It cannot, therefore, be recommended as a routine procedure.
Product Identification and Traceability
It is vital that unsterilized cans never become comingled with sterilized cans. It is also necessary to be able to clearly identify each of the cans from a given lot so that they can be checked against their processing records. Ideally, it should be clear which cans belong to a given retort batch at any stage after sterilization.
During the preparation and sterilizing operations, unsterilized cans should be marked to distinguish them from those that have been sterilized. This information should include the product, date of manufacture, and preferably batch or time of manufacture.
After sterilization, batches of cans should be checked off against their process records for double-seam evaluation, retorting, and cooling water tests so that they can be positively approved or rejected.
Product Recall Procedure
There should be a predetermined written plan, which is clearly understood by all concerned, for the recall of a product in case of an emergency. A designated person and appropriate backups should be nominated to initiate and coordinate all recall activities and serve as the point of contact with outside parties (health departments, media, customers, etc.).
Notification of recall should include the following information:
- Name, pack size, and adequate description of the product
- Identifying marks of the batches concerned and their location
- Nature of the defect
- Action required with an indication of the degree of urgency required
If a problem is identified with a batch or lot of canned goods, they must immediately be labeled as quarantined material and preferably isolated in a location dedicated for that purpose. Quarantined material must not be confused with goods of acceptable quality, as the consequences of misidentification could be extremely harmful to the consumer, the company, or both.
Emergency ProceduresIt is inevitable, even in the best run facility, that problems will occur from time to time. It is necessary, therefore, that documented procedures are in place. In the case of the sterilizing process, there should be instructions that de ne the actions to be taken.
If the product has been over-processed, the issue will normally be one of quality. If under-processed, the product will need to be further sterilized or destroyed. A full re-process may need to be more severe than the originally scheduled process due to changes in the product that affect heat transfer.
Positive Product Release
It is recommended to operate a positive release system in which approval for release of product is given only after quality checks of both product and process records have been made. Authority for such release should be clearly defined.
The management of a cannery should be able to prove at any time after manufacture that goods released conformed with specifications required for both processing and quality. In terms of consumer safety, this would include:
- Can seam evaluation records
- Retort operator’s log
- Automatic recorder chart on each retort
- (time, temperature, pressure)
- Cooling water chlorination checks
Each of these records should be reviewed before goods are approved for release. The retort operator should record any instances when processing conditions are outside specification and any actions taken. The recorder chart should be dated and contain sufficient information for product and batches to be correctly identified.
Manufacture of Frozen Peas from USA Dry Peas
The unit operations employed in the manufacture of frozen peas from USA dry peas, though similar in nature to those used in the manufacture of canned processed peas, include a number of essential differences.
If artificially colored peas are required, an appropriate coloring agent can be added to the pre-soaking water and to the water used for cooking the peas.
During canning, the texture of the peas is softened by the sterilization process. There is no equivalent to this during the preparation of frozen peas. Consequently, it is necessary to introduce a cooking stage.
This is achieved by extending the blanching to provide a total time of about 25 to 30 minutes at 203 degrees F (95 degrees C). Otherwise, a separate cooking process is introduced. At the end of cooking, using cold water, the peas should be cooled as rapidly as possible to a temperature not higher than 86 degrees F (30 degrees C) prior to the commencement of freezing.
The method used for freezing will inevitably depend upon the equipment available. Ideally, a flow freezer will be used so that the end product will be free flowing in nature. Packing, in this case, will take place after the completion of freezing.
Alternatively, cooked and cooled peas may be packed into retail containers and then frozen in a plate freezer or blast freezer. Such aggregation of the peas can, however, impact quality.
Frozen foods should be stored at temperatures no warmer than -0.4 degrees F (-18 degrees C) to inhibit microbial growth. Provided due care is taken with regard to all the aspects of hygienic manufacture, the product will remain safe for the consumer during the storage period. Prolonged storage can lead to deterioration due to chemical rather than microbial reasons.
Frozen foods require a frozen distribution system able to help ensure that the products remain safe and meet the desired sensory quality requirements. It is the responsibility of the food manufacturer to guarantee that the distribution system used is adequate for the intended purpose.
Chemical, Physical, and Structural Changes
During leblebi processing, carbohydrates and proteins are modified as a consequence of the heat treatment, including the carmelization of polysaccharides on the surface of the chickpeas. In addition, some acids are partially decomposed during roasting, while volatile acids are partially lost due to evaporation. Chickpea volume increases during processing at the same time the density and kernel weight decrease. The flavor can also change, especially as a result of the heating processes.
During the resting stage other changes can occur, some positive (e.g., ripening) and some negative (e.g., off flavor). The original raw chickpea is dense and contains no air spaces. But during roasting, the water inside the chickpea changes from liquid to vapor. Given the compact structure of chickpeas, this can cause an increase in the vapor pressure of water so that the steam that is generated triggers expansion during roasting. This can lead to development in the chickpea of a large number of air spaces in the cotyledons and give roasted chickpeas a porous structure and an opaque, chalky appearance.
The Growing Role of Legumes
Food legumes are important components in a healthy diet and make major contributions to good health around the world. Whether canned, roasted, fried, or used as an ingredient in soup, pulses offer a welcome alternative to the fast foods that have come to dominate the diets of so many.
The more we learn about the benefits of pulses and how best to process and prepare them, the greater the number of options will develop for their use. To promote their increased consumption, new and ever-more appealing products are required in the market. Food researchers are employed in just such a pursuit, attempting every day to find new uses beyond regional and ethnic preferences in an effort to introduce consumers around the globe to these delicious, versatile, healthful foods. See Appendix C for a collection of sample formulations.