Carbon Dioxide as Fermentation Byproduct, Applications And Usage

By Sam A. Rushing – Advanced Cryogenics, Ltd.
Special to The Digest                          

This article on CO2 usage in the food industry is one in a series for the applications which are predominant and important in the carbon dioxide industry. This subject is particularly interesting to the US Corn Belt region, which contains some of the nation’s greatest region for food processing in the form of beef pork and poultry processing, also the US southeast and south central region is the nation’s largest region for poultry processing. Much of the ethanol industry is concentrated in the nation’s regions which are also the regions which are the largest for much of the meat processing at large. Such regions hold low merchant prices for CO2, as well as abundant supply of CO2 to the merchant market. Additionally, many more ethanol plants are venting CO2 to the atmosphere than those which recover for the markets. The food industry is a major consumer of CO2 worldwide, and accounts for some 40% of merchant CO2 consumption domestically.

Over the decades, the food industry has consumed huge sums of CO2 for short to long term refrigeration requirements in many world markets. CO2 will always remain a viable refrigerant with added value as a minor anaerobic agent, which may have further value in food preservation applications. Some processors use CO2 for a long term, in a full range of applications in their processing plants, from IQF (individually quick frozen) applications, to use in grinding and commercial packaging with CO2 snow; to use as a gas flush agent in final consumer level packaging of food products.

When speaking of freezing in cryogenic environments v. mechanical refrigeration, cryogenic freezing has often been promoted on the basis of rapid temperature reduction, thus saving time, which represents economic savings; plus the further advantages in improved appearance, texture, and weight yield. This means a greater retention of water in the cryogenic freezing process v. mechanical freezing, and less damage to the food product on a cellular level. Some feel that the ice crystal within the cellular structure penetrates the cell wall less often when freezing rapidly v. over a longer and warmer mechanical environment; thus a greater weight yield, less fluid loss, as well as a better appearance. The appearance of a meat product, for example, can have a much improved appearance via cryogenic freezing over mechanical. All of this represents a number of advantages which cannot be demonstrated under the guise of mechanical refrigeration.

CO2 Applications in Food Processing

• IQF applications have probably represented the greatest amount of overall tonnage in CO2 sales from the greater food processing sector. Liquid storage is on site at the customer’s plant, and CO2 is piped to the freezer, or freezers, plus other points of application for ready use. The cryogenic freezers were once the full domain of the major gas companies during the decades past. In the United States, for example, these companies were the only source of cryogenic equipment technology, other than used options. Into the 1980s independent cryogenic equipment manufacturers came to be, which could then supply the customer directly, or supply the independent CO2 firms as well, with such technology. Cryogenic freezing technology is tried and true, with some nuances offered now and then over the years, which claim to offer more efficient use of the CO2 product, and achieve better results with specific valves, controls, and application equipment for CO2. The end result, however, with the often – subtle approach to improvements has been negligible. Any cryogen can only yield a certain amount of refrigeration value, and despite proprietary changes in the freezers, the end result is essentially the same. This is not a negative, statement, since, cryogenic technologies in the food industry offer an improved environment for true efficiency gain, via less time for refrigeration or freezing in a cryogenic machine v. a mechanical freezer, as well as often proven enhanced moisture retention for a food item, as well as improved appearance. The cryogenic application occurs via a wide form of freezers, using a linear, multiple pass, or spiral configuration, where liquid CO2 is delivered from bulk storage on site via insulated (usually type – K copper) pipelines, using working pressure from the storage vessels to deliver the liquid to the freezers. The freezer delivers a range of fine snow to vapor which often operate at temperatures of about -60degrees F. The goal is to lower the temperature of a food product, with a set residence time in the freezer, delivering a frozen product in a fraction of time of what mechanical refrigeration units can yield. The majority of IQF applications have historically been dedicated to freezing applications or temperature reduction applications in meat processing, v. processing other food products. The more expensive sector of the food industry has often been meat, which has been the major product frozen over the years past; however, more expensive entrees, and specialty frozen products also are good candidates for cryogenic freezing today, items with a good profit margin. The most inexpensive food products are not good candidates for cryogenic technology; this would be products such as tortillas. When calculating the need for a specific quantity of a cryogen, much data is well published and proven for residence time requirements within the freezers, average freezing point of the food product, % water content in a food product, and the definitions used in heat removal and freezing applications. Please see insert number one for a typical refrigeration and freezing calculation. These values are essential to properly size a freezer, as well as understand residence time, CO2 usage, and exhaust requirements from the freezer. Exhaust of spent gases have been considered in the past for reuse, that being recovery and liquefaction, however, the gas concerns are in the market to sell gas, not recycle spent gases. There are many scale of economics and technical challenges which would make this practical. On the other hand, when thinking about this subject, in today’s emissions reduction light, this is rather daunting. During my work in the merchant gas trade, I know this subject was broached, but not developed further.

• CO2 Snow or powdered dry ice is often an application alongside IQF applications for CO2 in settings, such as an operation which would grind meat into hamburger (thus using CO2 snow for temperature reduction); followed by an IQF application of a formed hamburger or other meat item. CO2 snow is included in liquid sales, when accounted for, if it is generated from a bulk, liquid storage tank in the customer’s plant setting; therefore it is an extension of liquid sales, v. product sold as dry ice alone. CO2 snow is essentially liquid CO2 flashed into solid CO2 upon entering atmospheric pressure, through a valve, from higher pressure piping, hoses, or storage containers which often have working pressures from 200 to 300 psig . CO2 snow is often used in grinding applications of meat or other food products, while the CO2 snow, as a solid refrigerant will sublimate and the added anaerobic effect against certain bacteria are features which LIN (liquid nitrogen) cannot be used as an effective substitute. CO2 snow is also produced and consumed in large meat and poultry packing houses for packing bulk meat products which are shipped; such as whole poultry or beef. CO2 snow, in such settings, can be applied via automated conveyor fed systems, or via manually opening valves and applying into a container. The application for snow may account for 20% of the product sold in the food industry, as a form of CO2, when applied in the markets.

• CO2 Gas Flush or gas purge applications in the food industry are an extension of liquid sales to the customer, and when accounted for by the supplier, when generated from bulk or micro bulk stations on the customer’s site. The CO2 gas flush can often be supplied from sublimated gases off the top of a bulk storage tank, or if heavy, may require a vaporizer for such applications. Gas flush applications can typically be found in packaged cheese operations, for example. The atmosphere within the cheese or food package is removed in favor of CO2, or a gas mixture, which can include oxygen or nitrogen, for example. This gas flush is probably less than 10% of the food industry sales; however, important in the food applications sector. Depending upon the goal sought, the end result is preservation, creating an anaerobic environment, or retaining a modified (packaged) atmosphere.

• Dry Ice which is little more than formed, extruded, or compressed CO2 snow. Today most food related dry ice is sold as a pelletized or so-called rice form. The rice form is otherwise a 1/8” size, reduced size in pellet. The rice form has gained worldwide acceptance over larger pelletized dry ice, ¾” for example. The smaller rice style dry ice would pack readily into boxes along with food product, and would blend in readily over larger dry ice product; however, is usually priced higher than the larger CO2 dry ice pellet. Today, there is probably a net growth in dry ice rice style sales v. other forms of dry ice, due to more acceptance and ease of application in the food industry and beyond.

Summary

The food industry has been extremely resilient, as the single major sector of the overall industry. However in a few regions, the food processing market is sometimes dwarfed by specific oil and gas producing regions for CO2 sales as a gas well stimulation agent. On the other hand, over the decades, the food sector has proven to be perhaps the most resilient form of sales of carbon dioxide; and the most interesting with respect to developing applications. Often a small food processing operation has only sufficient capital to start a freezing operation via cryogenic freezing, v. mechanical, due to a huge difference in capital cost on the front end. Over time, such a freezing operation may convert to mechanical refrigeration due to a substantial increase in size, if sufficient capital is available. Often such operations bring on additional processing lines or plants, which can use cryogenic technology to augment the mechanical refrigeration process (pre or post cooling); or in a blending or grinding line, CO2 snow may be the only choice, for example, representing a unique application in such a large plant. In the end, I have noticed that over the years, in order to sustain a significant business model in the merchant CO2 trade, food processing is a major component in the mix, and this has also been one of the most resilient and versatile forms of CO2 sales available to the gas concerns.

Sam A. Rushing, a chemist, is president of Advanced Cryogenics, Ltd., a CO2 consulting organization in business for almost 2 decades; which supplies all forms of CO2 consulting expertise to all sources of CO2 and projects surrounding the commodity, on a global basis. www.carbondioxideconsultants.com P.O. Box 419, Tavernier, FL 33070 USA, Tel 305 852 2597, rushing@terranova.net