J. Peter Clark

One does not usually associate refrigeration with the baking industry, but it turns out that the industry is possibly breaking new ground for all food processors as it deals with the need to replace conventional refrigerants and cooling equipment.

PROCESSINGThis is according to Anne Giesecke (phone 202-789-0300), Vice President, Environmental Affairs at the American Bakers Association, Washington, D.C., who has made herself knowledgeable about the many environmental issues that bedevil bakers, including water, volatile organic carbon emissions (VOCs), and, now, refrigerants.

The class of chemical compounds known as chlorofluorocarbons (CFCs) have many useful purposes because of their chemical inertness, thermodynamic properties, and low toxicity. However, it has been found  that these chemicals can decompose in the atmosphere and release chlorine, which then participates in the destruction of stratospheric ozone. This makes them ozone-depleting substances (ODS), according to the Environmental Protection Agency. Ozone helps protect us from excessive ultraviolet radiation.

Many useful and common refrigerants were CFCs, such as R-12 and R-502 (which contains a CFC). Under an international treaty, the Montreal Protocol, these refrigerants are no longer manufactured, and special provisions are required for their recovery from systems. As anyone needing to repair an automobile air conditioner has probably discovered, the consequence is a high cost because of scarcity of R-12 and the costs of recovery and purification.

Another class of compounds, hydrochlorofluorocarbons (HCFCs), are being manufactured for refrigeration and air conditioning applications for a limited time, until 2020, as substitute refrigerants. R-22 is an example and is widely used. After 2010, it will not be used in original refrigeration equipment but will still be available for ten more years (or until supplies run out) for maintenance of existing systems. R-22 is also used in polymer manufacture and so will be manufactured for many years, but about 50% of its use now is in refrigeration. This poses a dilemma for manufacturers that has not yet been resolved.

Chemical companies have developed substitute refrigerants with various properties. Some refrigerants are mixtures of other compounds. All must be of the class of chemical compounds known as hydrofluorocarbons (HFCs), which contain no chlorine and thus pose no threat to ozone. Examples include 134a, 404A, 507, 410A, 407C, and 417A. Different materials are appropriate for different refrigeration service.

For example, 404A and 507A are used for low temperatures, as in freezing; 134a is used for medium temperatures, as in coolers; and 410A and 407C are used for higher temperatures, as in air conditioning. Craig Thomas (215-419-7938), Product Manger at Atofina Chemicals, Inc., Philadelphia, Pa., a major supplier of HFCs (Forane refrigerants), explained these approximate distinctions, also pointing out that all the refrigerant suppliers provide essentially the same chemical entities, competing primarily on price and service. Atofina is the result of a merger between the French companies Elf Aquitaine and TotalFina. The other major suppliers are DuPont, with its Suva line, and Honeywell, through its acquisition of Allied Signal, with its Genetron.

Gordon McKinney (317-826-3200), National Sales Director of ICOR International, Indianapolis, Ind., explained that his firm imports a mixture of HFCs called NU-22 or 417A, which is offered as a direct replacement for R-22 and R-502 and is compatible with the mineral oil lubricants now used in refrigeration compressors. ICOR claims that its material can be used in all refrigeration ranges. Other HFCs require a different, synthetic lubricant called polyolester (POE). These lubricants can be hygroscopic and decompose if moisture contaminates them. Furthermore, when converting machinery to the new lubricants, several exchanges of oil must occur, creating a potentially large quantity of waste-contaminated lube oil onsite. With any change in refrigerant, there usually needs to be some adjustment to controls, perhaps including replacement of expansion valves and other parts. Capacity may also be affected. ICOR claims that its product reduces capacity slightly but also reduces energy consumption.

According to the U.S. Dept. of Justice, all this became important to the baking industry after a baking company experienced very high rates of R-22 leakage from mixers that were cooled by direct expansion. The connecting piping was subject to vibration. Even though allowable leak rates were quite high (35% of refrigerant content per year), rates exceeding these were experienced, probably because of poor maintenance. EPA concluded that bakeries posed a high hazard to releasing ODS to the atmosphere and began scrutinizing them more closely. Potential fines and penalties are high—thousands of dollars per day per unit (or appliance, as EPA calls them).

A Voluntary Partnership was negotiated between the baking industry and EPA, calling for immediate replacement of HCFCs (R-22 primarily), even though they are legal for use and available until 2020. Bakeries who made the replacement by May 31, 2002, are excused from a penalty for nonconforming appliances. The penalty was imposed by EPA and accepted by the industry in lieu of litigation and more-complex enforcement actions.

Thus, there has been a rush of demand for HFC refrigerants, especially those which can be used directly, such as 417A.

Replacement refrigerants must be accepted under EPA’s Significant New Alternative Policy (SNAP), in which proposed chemicals and mixtures are reviewed for safety in their proposed use. No single refrigerant is SNAP approved for all applications, but some, such as 134a, 404A, and 507, have fairly wide approval and have been accepted by most equipment manufacturers for use in their equipment.

One obvious modification that many bakeries are pursuing is to convert from direct-expansion cooling to indirect cooling using a fluid such as propylene glycol to cool equipment and cooling the glycol with refrigerant. This reduces refrigerant piping and ensures that if connections are exposed to vibration leak, they will leak a nontoxic and non-ODS material. In many food plants, refrigeration is provided by a central ammonia system. Ammonia poses its own hazards, but such systems are efficient and are usually large enough that they have their own trained operators and maintenance people.

The experience of the baking industry is likely to be extended to other segments of the food industry where CFC and HCFC refrigerants are now used in processing equipment. They will face the issues of whether to replace existing compressors, what refrigerant to use, what to do with waste oil and recovered refrigerant, and whether their systems can tolerate reduced capacity.

Extending Shelf Life Requires Systems Approach
Bread and other baked goods have several mechanisms for losing quality. Immediately after baking, they lose most of their aroma, so few consumers ever experience directly the great smell of fresh bread unless they make it themselves. Then, bread firms or hardens as starch recrystallizes or retrogrades. This is the mechanism that most enzymes used in baking affect. Finally, as bread ages, mold and other spoilage organisms can grow, especially when the product has higher moisture content. Thus, extended-shelf-life bread may stay soft but begin to show signs of mold growth and off (stale) flavors.

Carl Hoseney (785-537-5199), retired from Kansas State University and now President of R&R Research, Manhattan, Kans., said that the use of enzymes to extend shelf life of bread and other baked goods is becoming more common. Most enzymes affect the retrogradation mechanism. Some of the enzymes used are hemicellulases, pentosanases, and an alpha-amylase that generates maltose. Typically, these additives give a softer dough, which can create handling issues. These enzymes are also less tolerant to fluctuations in temperature in a baking oven, according to Tom Kuk (847-920-9885), President of the American Society of Baking, Winnetka, Ill. He said that studies of oven-temperature profiles using data loggers that travel through the oven have shown wide variations in temperature that can cause variations in moisture content. Since the dough for extended-shelf-life products is typically a bit higher in moisture to start, any variation in moisture loss during baking will noticeably affect final quality.

Extension of shelf life of bread requires a systems approach that involves formulation changes, including use of enzymes, emulsifiers, and other “moisture-controlling” additives, as well as process variation control and careful evaluation of mold-inhibition systems.

Maureen Olewnik (785-537-4750), Vice President of Research and Technical Services at the American Institute of Baking, Manhattan, Kans., agreed with Hoseney that the initial motivation for seeking extended shelf life was to provide two days off in a row for bakery workers. However, Hoseney observes that, in fact, bakers seem to be closing bakeries and distributing over a larger area but still working weekends. When Continental Baking, now part of Interstate Brands, was developing extended shelf life using enzymes more than 20 years ago, the issue was how best to modify the business model to take advantage of the longer code. At the time, bread was delivered almost every day, and returns were sold in thrift stores. Most fresh bakers follow the same model today, with relatively expensive distribution costs. At the same time, recruiting skilled labor to work traditional bakery hours (only one day off at a time) has often been difficult. Thus, there are two competing motivations for extended shelf life—reduced distribution costs and more attractive working conditions. Coincidentally, the consumer may benefit.

Acrylamide in Baked Foods Causes Concern
AIB’s Maureen Olewnik and David Lineback (301-405-8382), Director of the Joint Institute for Food Safety and Applied Nutrition (JIFSAN) at the University of Maryland, College Park, both mentioned the importance of current studies concerning acrylamide, a synthetic chemical that is apparently formed in cooking of some foods and can get into water as a contaminant. It is allowed at low levels in food and drinking water. At high doses, it is a suspected carcinogen.

A recent Stockholm University study that has received considerable press attention found relatively high levels of acrylamide in some grain-based foods and associated its presence with high-temperature processing, such as baking and frying. Many studies are now focused on what exactly the Stockholm researchers did, possible mechanisms of acrylamide formation, and whether it poses any risk to consumers. It is possible that modifications to processing methods will help address the issue, but it is premature to predict exactly how. In the meantime, government agencies in Sweden, the United Kingdom, and the United States have not recommended that people change their diets because of this study.

Contributing Editor
Consultant to the Process Industries
Oak Park, Ill.