Cryogenic System Rapidly Cools Eggs

On May 1, I visited Carolina Egg Co. in Nashville, N.C., where I attended a demonstration of a new system designed to rapidly cool shell eggs cryogenically. The system was designed by Praxair, Inc., Burr Ridge, Ill., in cooperation with North Carolina State University, Raleigh.

USDA’s Food Safety and Inspection Service regulations require that eggs be held at an ambient temperature of 45°F after processing and during transportation and retail storage. To conform with the FSIS regulations, the Food and Drug Administration has proposed that eggs in retail establishments be stored and displayed under refrigeration at 45°F or less and that the labels of containers of shell eggs that have not been treated to destroy Salmonella bear safe handling instructions.

It generally takes 7–14 days for eggs to cool from an initial (just-laid) temperature of about 110°F down to 45°F, but the cryogenic system uses liquid carbon dioxide to cool the eggs to that temperature within 80–90 seconds. This allows consumers to purchase eggs that are a week fresher than they could otherwise, essentially increasing the shelf life of the eggs without adversely affecting their quality. It also improves their safety, since microbial testing has shown reductions in Salmonella enteritidis (SE), the most common bacterial contaminant in eggs (see the accompanying sidebar for more information on egg safety activities).

According to David Farmer (phone 800-772-9247), Praxair’s Global Food and Beverage Marketing Director, Praxair and NCSU had both been working on the egg cooling challenge separately. Praxair began working with NCSU in 1992 and signed a research agreement in 1993. NCSU filed for a patent on the process in 1994. Praxair signed a licensing agreement with NCSU in 1998 and installed its patent-pending system for beta-testing at Carolina Egg last fall.

Patricia A. Curtis (phone 919-515-9514), Professor in the Dept. of Food Science at NCSU, said that she and other NCSU researchers Ken Anderson and Frank Jones (now at the University of Arkansas) came up with their idea to cool eggs cryogenically after a research project which showed how long it took the center egg in a pallet to cool to the ambient temperature. They obtained U.S. patent 5,474,794, “Rapid Chilling of Shell Eggs Using Cryogenic Gases,” in December 1995.

Various alternatives for rapidly cooling the eggs were considered, including spraying the eggs with nitrogen, immersing eggs in liquid nitrogen, spraying CO₂ in cartons, using CO₂in a standard freezing unit, and spraying CO₂ onto the eggs. Praxair chose direct CO₂ impingement as the optimum approach and developed a special cooling tunnel to accomplish it.

Farmer said that bacterial, shelf-life, and quality tests will continue through July for a comprehensive analysis to meet FDA requirements. USDA personnel will also be conducting inspections. The demonstration unit will be returned to Praxair after the beta-testing is completed in July. Construction of the first production unit will begin in June, and production equipment will be available in the fall. Praxair will supply equipment, installation, training, and CO₂ The only cost to the processor will be a technology license fee, anticipated to be in the neighborhood of 7–10 cents per dozen eggs.

Carolina Egg processes about 1 million eggs per day, 312 days per year, according to Bob Pike (phone 252-459-2143), the company’s Vice President, Egg Marketing. The chickens are kept in cages that are on a slight slant, so that the eggs roll into a trough and are conveyed into the in-line processing system. Everything is automated, including temperature, lighting sequence, and feeding. The eggs are never touched by human hands.

Here’s a comparison of the normal processing sequence and the cryogenic processing sequence:

Normal Sequence. The eggs are conveyed through the washing station, where they are spray washed with an alkaline detergent solution (pH approximately 11). The wash water is at 115°F and is recirculated with fresh water added. Then the eggs are rinsed with a sanitizing solution containing 200 ppm Cl₂ at 10°F higher than the wash water. The eggs then cross the candling table, where lights shine from below to illuminate the eggs, allowing the inspector to identify and remove eggs that are cracked or have blood spots or other defects.

The eggs are then blown dry and passed through a computerized egg grading system that includes digital cameras. The system, manufactured by Diamond Automation, Farmington Hills, Mich., identifies each egg, rejects checked (cracked) eggs, diverts dirty eggs back through the washing station, and weighs each egg, automatically sorting the eggs by size (weight) and passing them on to the proper packing line (there are 16) for cartoning and case-packing. They are then kept in a 45°F cooler for 7–14 days or shipped out within 24–48 hr in refrigerated trucks.

The eggs are at 110°F when they are laid, and they cool to 85–88°F by time they reach the washer. They pick up 12–14°F in the wash water. By the time they are cartoned, the temperature is 70–95°F, depending on the time of the year. The final temperature, Curtis said, depends on the season of the year and whether the eggs are from an off-line or an in-line flock. The egg temperature just prior to the wash could be 70–80°F for off-line eggs and 80–95°F for in-line eggs. The eggs can gain 12–14°F in the carton, since they will continue to heat for a while before they start to cool, even after being placed in the cooler.

Cryogenic Sequence. The sequence is the same as above, except that the eggs after being sorted by size are conveyed into the cryogenic cooling tunnel. The tunnel is 15 ft long and 5 ft wide and is modular, so that it can be as short as 9 ft long. The eggs pass through the tunnel on two side-by-side conveyor belts, each of which can handle 18,000 eggs/hr. Liquid CO₂ is piped to five injection heads at the top of the tunnel, where it expands, forming a vapor/snow mix that is directed onto the surface of the eggs as they pass through the tunnel. Roller bars rotate the eggs through the tunnel, for about 70 turns. Under this continuous direct CO₂ impingement, eggs can be cooled to 45°F in 80–90 sec. The carbon dioxide causes a thin (1–2 mm thick) layer of egg white to freeze on the inside of the shell, which acts as a heat sink and helps the eggs reach thermal equilibrium in about a half hour. The belt rate and fan speed can be adjusted to obtain a desired final temperature.

As the eggs exit from the tunnel, they are automatically placed into cartons containing 12 eggs (for retail sale) or flats containing 30 eggs (for industrial or foodservice use) and returned under the tunnel to crating stations, where the cartons or flats are placed into cases and shipped.

Besides rapid cooling, the system provides other benefits. According to Curtis, the cryogenic system produces eggs with increased membrane strength and twice the quality, compared to eggs normally cooled. Studies conducted by Don Conner at Auburn University have shown a 2–3 log reduction in eggs inoculated with SE. Microbial testing being conducted at NCSU has shown that even if the eggs are cracked, there is still a 2–3 log reduction after 8 weeks of storage.

Farmer added that since the eggs absorb a small amount of the CO₂, it has a bacteriostatic effect. NCSU researchers have been able to obtain an increase in shelf life from the current 30 days to at least 60 days, as well as an increase in egg quality, as measured in Haugh units—the greater the height of the white and the less spreading when an egg is cracked, the higher the Haugh unit. In addition, Curtis said, the process also strengthens the vitellin membrane around the yolk, so that the yolk stands firmer.

Pike said that egg producers generally use a sell-by date of 28–30 days or a use-by date of 45 days. The cryogenic cooling system extends the shelf life to 60 days, although 75–80 days have been reached before a decline in actual grades. Curtis said that the process adds 30 days to either the sell-by or the use-by date. In-shell pasteurization, Pike added, currently provides only a 30-day shelf life and may cause clouding of the egg white. The cryogenic system, in contrast, does not cause any deterioration of the egg and provides better functionality.

PATENTS
Shelf-stable complete pre-mixes that are combinable to form ready-to-cook mixes or food beverage products. U.S. patent 6,056,984, filed 8/10/1999, issued 5/2/2000 to A. Ekanayake et al., assigned to the Procter & Gamble Co. Describes shelf-stable complete premixes, separated into two or more components that are chemically and microbially stable. At least one component is a liquid with water activity greater than 0.85 and pH greater than 4.5. The components, when combined, provide all ingredients necessary to form uncooked mixes or food and beverage products.

Method for coating a whole meat muscle product with a powdered mixture. U.S. patent 6,054,154, filed 9/23/1997, issued 4/25/2000 to P.Y. Wang, assigned to Swift-Eckrich, Inc. Describes a method for applying a powder blend, such as smoke flavor and/or color, to a whole meat muscle product. A cooked, whole meat muscle product is placed on an electrically grounded support in a coating chamber to expose the surface to be coated. A powder blend that is at least partially soluble in cold water and a powdered moisture-absorbent agent are introduced into the coating chamber, and an electrostatic charge is applied to cause the powder blend to be attracted to and form a coating on the exposed surface

.Automatic deboning method and apparatus for upper half of poultry carcass. U.S. patent 6,059,648, filed 1/21/1999, issued 5/9/2000 to R. Kodama etal. Describes an automatic deboning method involving severing shoulder joints from an upper half of a poultry carcass, stripping wings together with breast meat, then removing white meat. The method accounts for variations in size and imbalance between the left and right sides.

Method for removing a casing from a food stuffed in the casing, and an apparatus therefor. U.S. patent 6,059,647, filed 10/29/1998, issued 5/9/2000 to H. Imaura, assigned to Ryowa Co., Ltd. Describes a method for automatically removing a flexible tubular casing from a food such as ham. It involves stripping one end portion of the casing from the food and pulling the stripped casing outward, so that it is peeled spirally from the food.

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Egg Safety Activities
The Food and Drug Administration and the U.S. Dept. of Agriculture’s Food Safety and Inspection Service are participating in an Egg Safety Action Plan whose goal is to reduce foodborne illnesses associated with Salmonella enteritidis (SE) in chicken eggs by 50% by 2005 and eliminate foodborne illnesses associated with SE in eggs by 2010.

Americans consume an average of 234 eggs per person per year. Although only an estimated 1 in 20,000 raw eggs in the United States contain SE, this involves nearly 3.36 million eggs annually, exposing a large number of people to SE. According to the Centers for Disease Control and Prevention, there were 300,000 cases of SE illness in 1997. Children, the elderly, and those with weakened immune systems are especially vulnerable. The costs associated with illness caused by SE are estimated to range from $150 million to $870 million annually.

USDA, in conjunction with FDA and CDC, conducted a risk assessment in 1998 to identify steps in the processing and handling of eggs from farm to consumer that increase the risk of illness from this pathogen and to identify and evaluate potential risk-reduction strategies. The risk assessment estimated that of the 47 billion shell eggs consumed annually as shell eggs, 2.3 million are SE-positive, exposing a large number of people to the risk of illness. The risk assessment also determined that an 8% reduction in illnesses would occur when all eggs are maintained at an air temperature of 45°F throughout shell egg processing and distribution.

According to FDA, at the time that eggs are packed, the internal temperature is typically 70–80°F. Most processors hold packed eggs in coolers at an ambient temperature of 45–60°F. USDA estimates that shell eggs are held for 2–72 hr at 45–90°F at the processor, 1–24 hr at 45–90°F during transportation, and up to 60 days at 40–90°F at retail. These data indicate that, especially at retail, eggs are being held for long periods of time at temperatures that will not inhibit growth of SE. The internal temperature of the eggs when they are transported ranges between 50 and 80ºF, depending on the egg’s temperature at the time of packing, the way the eggs are packaged, how the crates are packed and stacked, and the length of time they are in the cooler before they are shipped.

Also according to FDA, refrigerating shell eggs at 45°F or less greatly extends the time that an egg can maintain its natural defenses against movement of contaminating bacteria to the nutrient-rich yolk and therefore substantially reduces the likelihood that any SE that is present will be able to increase in numbers. There is also evidence that cooling eggs reduces the heat resistance of SE, making any microorganisms that may be present more likely to be killed when the egg is less than completely cooked.

The President’s Council on Food Safety, established in August 1998, identified egg safety as an issue that warrants immediate action. Last July, FDA and FSIS committed to developing an action plan to address the presence of SE in shell eggs and egg products using a farm-to-table approach. The agencies held a public meeting last August and used input from the meeting to develop the Egg Safety Action Plan, which was announced by President Clinton in December.

In March and April, the agencies held two public meetings that focused on specific egg safety issues, including on-farm production, packer shell egg processing, egg products processing, research, and egg safety at the retail, foodservice, and consumer levels. They will use the input from the meetings to help develop new regulations for eggs. The proposed regulations are scheduled to be announced this fall, and a final rule is expected to be published in 2001 and implemented in 2002.

Under the action plan, FDA will develop standards for the egg producer; the states will provide oversight and enforcement on the farm; FSIS will develop standards for both shell egg packers and egg product processors and provide inspection and enforcement for both; and FDA and the CDC will conduct surveillance and monitoring activities, with CDC focusing on human health and FDA on the food supply.

Under the new plan, egg producers and processors will implement one of two strategies to improve the safety of shell eggs and processed egg products: (1) rigorous on-farm agricultural and sanitation practices, extensive testing for SE, and diversion of SE-positive eggs to pasteurization or cooked product; and (2) implementation of new technologies to kill SE, such as in-shell pasteurization, at the packer stage of production. More information about the Egg Safety Action Plan is available on the Internet at www.foodsafety.gov.

United Egg Producers, Atlanta, Ga., a trade association representing about 80% of all the egg production companies in the U.S., used research from a pilot project funded by USDA to develop its 5-Star Total Quality Assurance Food Safety Program. The program, designed to assist egg producers, processors, and marketers in establishing programs that meet a set of guidelines for food safety, covers the five critical control points from production to consumer use: cleaning and disinfecting of poultry houses; rodent and pest elimination; proper egg washing; biosecurity; and refrigeration at 45°F from packing through delivery. The program also includes a testing procedure for validation. More information is available from UEP at 770-587-5871 or www.unitedegg.org.

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Products & Literature
CONVECTIVE DRYING SYSTEMS are the subject of a 4-p brochure that describes their design features and benefits, as well as applications in the areas of bakery/bread, cereals/grains, nuts/seeds, starch/food additives, beans/rice, and candy/snacks. For a copy of “Food Processing: 21st Century Dryer Design Boosts Performance . . . and Profits,” contact National Drying Machinery Co., 2190 Hornig Rd., Philadelphia, PA 19116 (phone 215-464-6070, fax 215-464-4096, www.nationaldrying.com) —or circle 316.

SMALL VIBRATORY FEEDERS are described in 16-p brochure VB-3005A. The brochure explains the Hi-Vi electromagnetic drive and other engineering advances that assure precision feeding and flow of dry bulk materials. For a copy, contact Eriez Magnetics, P.O. Box 10608, Erie, PA 16514-0608 (phone 800-345-4946, fax 814-838-4960, www.eriez.com) —or circle 317.

STEAM BLANCHER/COOKER, the Turbo-Flo®, is said to process canned or frozen potatoes, vegetables, fruits, meats, and poultry up to 30% faster and with less floor space required than conventional water blanching equipment. The convection-heating dynamics transfers heat efficiently, and the fully enclosed and insulated blancher chamber with hydrostatic water seal eliminates evaporation, the primary cause of efficiency loss in steam blanchers. The unit can process peas or corn at up to 30,000 lb/hr. For more information, contact Key Technology, Inc., 150 Avery St., Walla Walla, WA 99362 (phone 509-529-2161, fax 509-527-1331, www.keyww.com) —or circle 318

FILTRATION SYSTEM, the MicroMax-30, uses centrifugal force to remove particles as small as 5 microns from hot frying oil. This allows less oil to be lost in extracting fines, improving quality and preventing free fatty acids from accumulating in the cooking oil. For more information, contact Stein DSI, 1622 First St., Sandusky, OH 44870 (phone 800-447-2630 or 419-627-4342. fax 419-626-9560)—or circle 319.

BATCH FLUID BED SYSTEMS for solids processing are available in sizes ranging from laboratory and pilot scale to large production units. Processes include bottom spray coating, top spray coating, layering, spray granulation, instantizing, cooling, and drying. For more information, contact Niro Inc., 9165 Rumsey Rd.,Columbia, MD 21045-1991 (phone 410-997-8700, fax 410-997-5021)—or circle 320

by NEIL H. MERMELSTEIN
Senior Editor