Fermentation
Fermentation procedures, first proposed in 1984 and not commercially tested until 1992, are a more demanding but safer and perhaps more cost-effective method of preserving carcasses until the industry is prepared to handle their further processing and reuse. In fact, fermentation safely disposes of poultry mortalities by “processing” them on-site. The pickled carcasses can be stored until the end of the growing cycle or until sufficient volume is attained for delivery to a rendering plant.
Fermentation begins in a grinder. The carcasses are ground into small particles (each piece measures roughly an inch) and a fermentable carbohydrate is added to the container. The grinding action disperses and mixes anaerobic lactic acid-forming bacteria found naturally in the birds’ intestines; the carbohydrate provides the bacteria “opportunity” to ferment the ground mortalities; and the result is the production of volatile fatty acids and a reduction of pH — from 6.3 in the fresh tissue material to the 4.5 pH of the carbohydrate mixture.
It is the decline in pH that effectively preserves the birds’ nutrient contents. In sum: the activity of anaerobic bacteria (Lactobacillus sp., which are found naturally in poultry) converts the carbohydrate into lactic acid and lowers the pH to less than 5.0, thus inactivating the pathogenic microorganisms in the carcasses and preserving the organic materials.
The first commercial on-farm fermentation system was designed to accommodate daily broiler mortalities. It consisted of a grinder and tanks housed in a shed equipped with electricity and water. The grinder was constructed to incorporate the carbohydrate during the grinding process. The carbohydrate source may be sugar, whey, corn, or molasses, depending on which of these materials is most available to the grower. In the first commercial facility, corn was added on a 20-percent weight-to-weight basis.
The mixture of ground corn and mortalities passes from the grinder directly into an enclosed tank where the fermentation process takes place. Sugars in the corn are converted to lactic acid; the pH level drops; and within seven to 10 days, the lactic acid bacteria increase sufficiently to preserve the carcass nutrients. The fermented material can be kept in a stable state for several months, easily accommodating its transport at the end of a grow-out cycle.
The equipment should be cleaned routinely. After each use, the grinder can be flushed with a minimal amount of water that can be rinsed into the holding tank. The entire grinder should be disassembled and thoroughly cleaned each month.
The initial investment in this process is relatively high — for the building, grinder and tanks, and their installation. The first commercial system cost $8,200; the value placed on the fermented product was $.02 per pound. The net cost of fermenting the mortalities per pound was
estimated at $.045 per pound, or fractionally less than composting ($.048) and almost half the cost of incineration ($.089, using 1992 figures).
Mortalities are a continuous and growing challenge for the poultry industry. The fermentation process is clearly a technology that meets the biological and environmental criteria required for the proper disposal of on-farm mortalities. Growers and their companies must carefully weigh these advantages against the managerial and economic trade-offs involved in selecting this practice.
Acid Preservation
Preserving foodstuff by acidification has been a widespread practice in agriculture. This method of preserving dead birds is the same as the fermentation process except that propionic, phosphoric, or sulfuric acid is added to the poultry carcasses, which are kept in an airtight, plastic container. Sulfuric acid may be preferred because it (1) retards spoilage, (2) excellently preserves the carcass, and (3) is relatively low in cost. However, safe handling and storage of the acids on-farm are important concerns.
Carcasses can be punctured with a blunt metal rod rather than placed through a grinder. Punctured carcasses can be separated from the acid solution without the accumulation of sludge in the holding container.
Selecting a Holding Method
The product resulting from acid preservation and lactic acid fermentation reduces the transportation costs associated with rendering by 90 percent. What is more important, however, is that these processes eliminate the potential for transmitting pathogenic organisms into the rendered products or the environment.
In an expanding poultry industry, the production of manure and mortalities will only increase. Producers should contact the renderers in their area to determine which holding and transportation methods are acceptable, and they must increase their search for safe, cost-effective disposal and reuse methods. Every possible safe method should be explored until each grower determines the method most compatible with his or her situation and management abilities. Rendering, like composting, adds value to the end product that can help offset mortality management costs.
References
Blake, J.P. 1993. Mortality Management. Presentation. Poultry Waste Management and Water Quality Workshop. Southeastern Poultry and Egg Association, Atlanta, GA.
Blake, J.P. and J.O. Donald. 1995.Fermentation of Poultry Carcasses. Circular ANR-955. Alabama Cooperative Extension Service, Auburn University, Auburn, AL.
Lomax, K.M., G.W. Malone, and W.W. Saylor. 1991. Acid Preservation for Poultry Carcass Utilization. Paper No. 91-4051. American Society of Agricultural Engineers, Albuquerque, NM.
Murphy, D.W. and S.A. Silbert. 1992. Preservation of and Nutrient Recovery from Poultry Carcasses Subjected to Lactic Acid Bacteria Fermentation. Journal of Applied Poultry Research 1(1):66-74.