Cryogenics and Food
The industrial gas industry provides a host of products and services related to food. The various gases have useful and sometimes fascinating applications in food industry.
“The food industry is not a homogenous industry. The needs of customers processing hamburger vs. poultry vs. strawberries vs. seafood, for example, are very different,” according to William Roberts, Marketing Manager, Food, Air Products and Chemicals, Inc. In turn, the techniques offered by the industrial gas industry in service to the food industry are extremely varied.
Industrial gases (not all of them cryogenic) are used to promote seed germination, to enrich the greenhouse environment and promote plant and flower growth. Oxygen is added to water in aquaculture to enhance yields. Special gas mixtures are used for pre-harvest insect control and fruit ripening. Gases are used to stun red meat animals and poultry during slaughter, and fish prior to freezing. This is not only kinder to the animals, but it produces a better quality product.
An interesting application from BOC Gases is a patented carcass injection system it says reduces boning labor by fifteen percent at cattle and hog processing facilities. CO2 or nitrogen vapor is injected directly into the natural seam of the meat carcass, causing a ballooning effect of the meat. This helps separate the membranes between the muscle groups and from the bone without damage to the meat, resulting in increased boning efficiency and reduced labor. The vapor is passed through a regulator and filtering process to ensure USDA standards are met. The vapor is injected into the meat with a lightweight, durable injection gun with a specially designed needle that safely provides optimal delivery of gas vapor to the carcass. (Source: Mark Grace, Technology Director for Food, BOC Gases)
Bakery Industry
In the bakery industry, nitrogen is the perfect medium for freezing delicate products like muffins, scones and cakes. LN2 vapor is also used to cool baked foods. Cookies that take 13 minutes to cool from 130°F to 75°F with conventional methods can be cooled in one minute with liquid nitrogen. Space requirements are also reduced. (Baking and Snack)
Cryogenic systems cool, chill or freeze a wide variety of bakery and related snack products, from cakes and cookies to bread dough and bagels. They offer shortened production time—as much as 50 percent or more. This is an advantage for products requiring several processing steps, including multiple layered, coated and iced products that must be quickly set to facilitate the next processing step.
Labor and handling are reduced since bakers can immediately package the product for a continuous, in-line operation. Yields are increased, with product prevented from sticking to the belt, decreasing product losses and increasing processing speeds. Cryogenic freezing also increases production flexibility, enhances processing capability, improves product quality, reduces maintenance time and reduces space and capital requirements. (Source: Air Products and Chemicals, Inc.)
BOC Gases points out that its Flour Chilling System improves the quality of bakery products and provides operating efficiencies by ensuring accurate and consistent flour temperatures, especially in extreme heat. Temperatures vary within +1°F, ensuring repeatable batch-to-batch dough quality. Customers get as much as one percent gain and up to 59 percent reduced waste in their products. The fully automated cryogenic process eliminates excess moisture, unreliable timing and labor costs associated with ice. The process improves dough machinability.
Both carbon dioxide and nitrogen are used in the beverage industry, and nitrogen is used in sparging solutions to reduce the negative effects of dissolved oxygen in brewery products, beverages, milk products, oils and fats. Blanketing with inert atmospheres improves operational safety, product quality and preservation of edible oils. Industrial gases are also effective for fat and oil hydrogenation and cryogenic crystallization for dairy, liquid, bakery and confectionary products.
MAP/CAP
Modified Atmosphere Packaging (MAP) and Controlled Atmosphere Packaging (CAP) use a gas or a gas mixture to maximize a food product’s shelf life, safety, purity and freshness. Because air is replaced, bacteria and mold growth is retarded, shrink and waste is reduced, and taste, color, vitamins and sensory appeal are preserved without the need for vacuum packaging or other chemical preservatives. Droplets of liquid nitrogen are dispensed to provide quick and accurate inerting to minimize fat rancidity during storage of nuts, milk products, peanut butter and dried potato.
Beverage industry packaging applications include reduction of in-can oxygen levels and in-line systems that provide rigidity, enhancing the stackability of cans and plastic bottles.
We all know that carbon dioxide is essential for carbonation. Also, CO2/nitrogen gas mixtures are used in beverage dispensing.
Controlled atmosphere and pressure transfer systems establish and maintain required conditions for stored fruits, vegetables, flowers, dairy products and liquids. Carbon dioxide, nitrogen and special gas mixtures provide residue-free fumigation for post-harvest disinfestation of grains, cereals and nuts.
LN2 and combination cryogenic/mechanical in-transit refrigeration (ITR) systems maintain the quality and safety of refrigerated foods during transport. Using cryogenic ITR provides consistent airflow to uniformly maintain desired temperatures and retain food product integrity and freshness. Such systems can handle ambient, chilled and frozen products in the same delivery vehicle or storage space.
Gas mixtures also are used for reliable and cost-effective distribution of fresh produce, meats and seafood over long distances. Advanced atmosphere control technology manages temperature, humidity and gas mixture inside the transport container.
Ancillary operations which are served by the industrial gas industry include process and wastewater treatment, condensate and food washing water recycling systems, welding shop gases and equipment, refrigerants and laser gases for labeling. (Source: BOC Gases)
Food Freezing
The major process we will study is food freezing in its many forms, using ammonia, carbon dioxide or liquid nitrogen. When discussing cryogenics and food processing, we usually take a broad definition of the term “cryogenics,” extending it to include carbon dioxide, which in its various forms is a very useful food cooling substance. But the most common cryogenic material used for cryogenic freezing is liquid nitrogen.
“The objective of both refrigeration and freezing is to remove sensible and latent heat from a food. Freezing—the conversion of the aqueous part of a food from water into ice—preserves food by dropping it to a temperature at which spoilage organisms are unable to grow and chemical reactions that affect product degradation are slowed or inhibited. Freezing basically makes water unavailable for microorganisms and for chemical reactions.
“To freeze a food, the product must first be cooled to the transition point of water, 32°F (0°C), by placing the food in a still-air freezer (sharp freezing), passing cold air over the product (convection), bringing the food into contact with cold plates (conduction), immersing it in a cryogenic fluid (cryogenic) or using a combination of these processes.
“Cryogenic freezing is defined as freezing at -75°F (-59°C) or below.” (Baking & Snack, April 1998) High-velocity cryogen immediately impacts heat transfer from product. Cryogen temperatures can reach as low as -320°F, while overall internal freezer temperatures can reach -150°F.
This freezing technique exploits features of nitrogen that make it an ideal natural refrigerant for use in the food industry. In its liquid form, nitrogen, at 196°C, is one of the coldest substances, and is completely inert, colorless, tasteless and odorless. As a natural part of the earth’s atmosphere it has no adverse environmental effects, unlike other refrigerants. The same can be said of carbon dioxide, except for its reputed effect on the ozone layer.
Benefits of LN2
Many benefits result from use of liquid nitrogen in freezing: the high quality resulting from individually quick freezing (IQF); preservation of texture when products are thawed; improved yield resulting from less moisture loss; products frozen in LN2 do not stick to belts or get misshapen by conforming to the shape of the belt; there is no need for specialized maintenance personnel and production rates are very high.
That cryogenic freezing is much quicker than mechanical freezing is evidenced by a small food processor cited in Food Engineering, February 1997, as having cut processing time for frozen prepared foods, primarily breakfast foods for airlines, hospitals, schools and casinos. Their business was expanding and the old mechanical freezer took four or five hours to freeze product. Nitrogen tunnels from Praxair, Inc. cut processing time down 600 percent—to three to four minutes! The customer was also pleased with quality improvements: color and flavor retention was enhanced with the quick freezing, freezer burn was eliminated and dehydration was reduced, increasing yield.
Roberts of Air Products discussed many aspects of cryogenic food freezing. He said the industry is dominated by mechanical spiral freezers that use ammonia as a refrigerant, operating at about -40°F, but that trends in today’s food processing industry bode well for the growth of cryogenic freezing. As consumers dine out more and cook less at home, the demand for more ready-to-serve food for both home consumption and use by large restaurant chains is increasing.
Further Processing
This requires a lot of “further processing.” That is, producing value-added product in response to the trend for less and less on-site preparation and more heating up of pre-prepared foods. A visit today to the kitchen of a major restaurant chain will find not a chef preparing meals from scratch, but rather lesser skilled workers who are heating up meats that have been marinated and even pre-cooked, salads pre-packaged and possibly inerted with nitrogen; desserts prepared by a “gourmet” bakery and possibly frozen with LN2, frozen vegetables, and par-baked bread. We can project a growth of such chains, and thus a growth in the demand for cryogenic processing.
Another aspect of this trend is that as the demand for value-added foods increases, the issues of better yield and quality becomes more critical. Here is where cryogenic freezing excels. The faster a product is frozen, the more water it retains. The more water it retains, the higher the yield. The higher the yield, the more income for the processor. So cryogenics should continue to be a critical part of food processing because it delivers higher quality with less dehydration.
Types of Cryogenic Freezers
As the food industry develops, the different types of customer require different freezing technologies and skill sets to solve their freezing problems. Therefore, manufacturers continue to develop different types of freezers.
Traditional tunnel freezers were the first type of freezer, produced in response to the demands of the infant hamburger patty business. They are now used broadly in all segments of the industry, with prepared foods, ethnic foods, appetizers and airline-type products.
Tunnels have a cold end and a warm end. LN2 is typically sprayed at the exit end and cold gas drawn forward toward the entrance. Gas is exhausted as warmly as possible. Tunnels are modular and can be configured in length and width to meet customer needs. The longer tunnels handle more volume. The longest are generally about 60-70 feet. They are limited by the limits of customer facility space.
Conversion to LN2
Tunnels either use CO2 (-80°F) or LN2 (-150°F). A recent article in Food Engineering, October 1998, cited a case in which AGA Gas helped a customer processing value-added potato products to slash annual freezing costs by 27 percent ($9,000 in the first month) by changing from CO2 to LN2 in its straight tunnel freezer. The magazine says AGA advised that although LN2 can be more expensive than CO2 per pound, it is far colder (-320°F versus -109°F) and provides up to 30 percent more cooling capacity per pound in some applications. The customer’s freezing costs have dropped from 4.6 to 3.2 percent of product costs—the cost of goods sold. In seven months, the customer saved $37,000 in freezing costs over the same period in the previous year and produced an additional $440,000 worth of product.
Spiral freezers operate much like a tunnel, CO2 at -80°F and LN2 at -100°F. Spirals have uniform temperatures throughout and provide lots of freezing within a limited space. There can be as much as 400-500 feet of belt inside. Spirals are used in high volume applications because a lot of retention time is needed to process 5-6,000 lbs./hr. of product.
LN2 immersion freezers use a bath of LN2 to crust-freeze the surface of a variety of products which are literally dropped into the bath. They are usually conveyed into a tunnel or spiral freezer to finish the freezing. Immersion is ideal for a high water-content product such as shrimp. The outside of the product is frozen to prevent pieces from sticking together and forming a frozen ball. It is also useful in the poultry industry with skinless, de-boned chicken breasts, for example, which are very wet and can conform to the mesh of the conveyor belt. Immersion prevents this and freezing is completed in a more traditional ammonia-type freezer or cryogenic spirals or tunnels.
CO2 immersion freezers are not possible, since CO2 is a liquid only at high pressure; at atmospheric pressure it turns to snow, so there really can’t be a bath for immersion. Alternative approaches with CO2 snow are used, however.
CO2 As a Spot Cooler
CO2 snow can be applied at many stages in food production process, offering versatile solutions on the line.
BOC Gases, for example, produces a dual horn snow generator they say provides “a simple, cost-effective method to control product temperature in processing or storage and handling operations.” This generator deposits CO2 snow at a low velocity into open containers and blenders. The horns deliver granular snow without loss from snow blowout sometimes encountered with conventional snow horns. The generator “goes everywhere” in the processing plant to chill perishables.
Another CO2 application from BOC Gases is the Dri-Pack chilling system for chilling of perishables directly in their packing boxes. Adjustable and adaptable, this simple to use the system places snow precisely.
Small Volume Immersion Freezer
Air Products introduced a new CRYO-QUICK RH LN2 immersion freezer at the recent International Poultry Exposition in Atlanta. This is a small immersion freezer that can be used with other freezing systems or with an Air Products tunnel. The new freezer has a belt that is half the width of their other RH immersion freezers, specially designed for smaller throughput to serve the needs of smaller volume customers. These freezers control immersion times by changing the amount of belt that passes through the LN2 or by changing the belt speed. This freezer is used to produce IQF poultry products, seafood, fruits, vegetables and beef, and increases quality of products which have been diced, pre-cooked, breaded and/or marinated. The company has a broad line of immersion freezers.
New Technologies
Last fall, Air Products introduced a breakthrough technology—the Closed Cycle Air Refrigeration (CCAR) System—which uses high-pressure air to economically produce refrigeration at temperatures ranging from -60°F (-50°C) to -150°F (100°C). The first CCAR system is in operation at Eastman Kodak Company’s production facility in Rochester NY and has replaced a conventional low-temperature mechanical refrigeration system to cool a processing fluid. It produces 50 tons (210kW) or refrigeration at -100°F (73°C). Standard units up to 200 tons (700kW) are planned; specialized units will be produced as the market demands.
CCAR technology is expected to find application in the food processing, pharmaceutical and petrochemical industries. The R&D was undertaken with Toromont Process Systems, Houston, and partially funded by the National Institute of Standards and Technology (NIST) Advanced Technology Program. The technology is an environmentally friendly method of producing refrigeration to replace ammonia and/or chlorofluorocarbons.
The patented CCAR technology uses the same concept as air separation and is similar to ammonia refrigeration. High pressure air goes through a heat exchange coil inside the freezer. The high pressure air exchanges with air in the freezer to produce -100°F temperature. It recirculates high pressure air, using no cryogens.
CCAR and Food
Roberts said they plan to apply CCAR technology to enable food processors to increase yields by one to five percent by reducing dehydration, enhance throughput through faster freezing rates, and improve product quality through increased moisture retention and the formation of smaller ice crystals. The process is aimed at customers whose business has grown and whose freezing needs are very large. They may have started out with cryogenic freezing, but because of the costs of cryogens, they switch to ammonia refrigeration because it is significantly cheaper. CCAR brings the advantages of cryogenics at close to the costs of ammonia refrigeration. Because of its larger fixed costs, however, it is suited to very large operations or to processors who are located in an area where cryogen is hard to get and too expensive.
ChillCan
BOC Gases, in conjunction with the Joseph Company, have a new self-chilling can that was approved by NASA for use on last fall’s Space Shuttle. Studies have found that the cans using BOC gases’ patented CO2 process show a dramatic improvement in environmental impact over the CFC and HFC refrigerant originally used with the can.
It’s thought that the can would be an environmental improvement in developing countries where refrigerators using CFCs are still used. The self-chilling can could completely displace refrigerated vending machines. Studies will continue at the University of North Carolina by Professor Mike Overcash.
In the ChillCan, low pressure CO2, which acts as the coolant, is held in the heat exchangers in the inner compartment of the can. The drinker pushes a button to start the chilling process and the drink is cooled by about 15°C in two or three minutes. The CO2 used in the process is obtained by recycling from industrial processes. Large scale production is expected for the cans.
The Cryo-Zat™ System from Air Products and Chemicals was exhibited at a recent trade show, where it produced ice cream molded into a logo and 3D chocolate teddy bears on a stack. This revolutionary new ice cream processing system allows 3D high definition premium ice creams to be formed without the ice cream sticking to the molds, a problem that has prevented the marketing of such products until now. The process is still in development and testing, but recently won a technology development award.
Air Products has developed a new Cryo-Cool™ chiller that can halve the cooling time for liquids using a new vacuum technology. The process is suited to food processors supplying sauces and gravies, because its rapid chilling of cooked liquids minimizes the risk of bacterial contamination. The Cryo-Cool process betters the speed of its faster alternatives at much lower costs, making it ideal for small to medium enterprises. Another advantage is that aromatic oils and flavors which can be lost through evaporation in other chilling processes are reabsorbed. The customer reported that the process reduced the cooling time from three hours to under an hour and eliminated the need to transfer sauce into smaller containers for further cooling.
BOC on the Road
BOC Gases has established a mobile food lab and provides mobile food equipment, including more than eight portable, mini-batch freezers, allowing customers to immediately test cryogenic freezing and chilling technology onsite. The lab can perform a variety of analyses to compare food quality under an assortment of conditions.
BOC Gases Director of Food Marketing Bill Baker commented that the mobile lab allows BOC to test product that is fresh, to test a variety of products at the same time, and to get as close to in-plant process conditions as possible. The mobile labs are self-contained trailers mounted with a 10-foot tunnel freezer and a 2.5-ton cryogen tank.
The lab can also be equipped with a mixer/blender and bottom injection CO2 nozzles for food chilling demonstrations. The smaller portable systems, or mini-batch freezers, are demonstration units that can be shipped or transported to the customer for testing. Dewars of LN2 or CO2 can be obtained from BOC or a local distributor for the testing.
Self-Assessment Guide
Air Products has developed a new self-assessment guide to assist food processors in quantifying the economic benefits they can achieve by integrating its LN2 freezing systems into their processing operations. The guide includes a worksheet which can be used to calculate food production rates, the estimated amount of LN2 needed per pound of production, and ultimately, the cost per pound to freeze a particular food. The guide also helps food processors to calculate other potential savings—such as yield improvement—which may offset LN2 costs. Ask for Pub. No. 332-9803.
References
- AGA Gas, Jeff Cass, Program Market Manager, Food and Industrial Cryogenics, 6055 Rockside Woods Blvd., P.O. Box 94737, Cleveland OH 44101-4737, 216-573-7818, 216-573-7873, jeff.cass@agagas.com
- Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown PA 18195-1501. Food Technologies Division, 800-434-4267 ex. 24, http://www.airproducts.com/gases/food.html
- William J. Roberts, Marketing Manager, Food, Air Products and Chemicals, Inc., 610/481-6589, robertw2@apci.com
- John Summers, European Marketing Manager, Food Processing Group, Air Products and Chemicals, Inc., +44 1932 249473, fax +44 1932 249786
- Katie McDonald, 610/481-3673, mcdonace@apci.com, www.airproducts.com
- BOC Gases, Mark Grace, Technology Director for Food, 575 Mountain Ave., New Providence NJ 07974, 908/771-1279. Pete Gavigan, 908/771-1512, www.boc.com
- Praxair, Inc., 39 Old Ridgebury Rd., Danbury CT 0677810, 800/772-9247; Debra Olsen, Marketing Communications Manager, Food Segment, Praxair, Inc., 7000 High Grove Rd., Burr Ridge IL 60521, 630/320-4000
- Baking and Snack, Christine McWard, Editor, 4800 Main Street, Suite 100, Kansas City MO 64112, 816/756-1000, fax 816/756-0494, bakesnack@sosland.com, www.sosland.com
- Food Engineering, Joyce Fassl, Editor in Chief, Chilton Company, One Chilton Way, Radnor PA 19089. 610/964-4440, fax 610/964-4273, jfassl@chilton.net, http://www.chilton.net
