Carcass Sanitising and Primal Washing
Eben van Tonder
Jan 2017 (Updated 2024)
Introduction
In certain environments, bacterially contaminated pork carcasses are inevitable. The old principle of garbage in, and garbage out applies to a meat factory also. One can not make excellent products from bacterially contaminated meat. Good hygiene starts far back in the supply chain.
The Case Against Carcass and/ or Primal Cut Washing
The Meat Inspectors Manual for Abattoir Hygiene, published by the Directorate of Veterinary Services at the South African Department of Agriculture(2007) makes two important points.
The first one is that “microbes firmly attach to meat and skin.” They explain that ” this process is not yet well understood but it appears to become irreversible with time – the longer organisms remain on the meat the more difficult it becomes to remove them. In poultry processing, the contact period between the meat surface and contaminating organisms is reduced by washing carcasses at intermediate points during processing before attachment occurs.” They then caution that the principle should not be applied to larger carcasses because too much wetting spreads rather than removes contamination. In fact, when small volumes of faeces, intestinal contents, mud or soil are spread over the carcass by rinsing, the clean areas of the carcass can become quite heavily contaminated. This is the reason why carcasses should not be rinsed. Wet carcasses also tend to spoil more rapidly – especially if wet and warm. Un-split carcasses should never be washed and split carcasses should only be partially washed under the lowest pressure possible.” (Meat Inspectors Manual)
They summarise their position as follows, “The meat under the skin of a healthy animal is sterile. The slaughtering process must be aimed at keeping the bacterial load on the newly exposed meat surface as low as possible and all efforts should be made to prevent bacteria from being deposited on the carcass. It is necessary to ensure that nothing that touches the exposed meat is contaminated with microorganisms. By using the correct slaughtering techniques with this aim in mind, a high degree of sterility is indeed possible under commercial conditions. This is shown by the fact that fresh meat when vacuum packed and maintained at 0 °C, as produced for export in Australia, New Zealand and SADC countries, has a microbiological shelf-life of up to 6 months.” (Meat Inspectors Manual)
The question is, however, what to do if good abattoir practices do not exist. If either the carcass or the meat may very likely have been contaminated? In one West African country, for example, I visited abattoirs in 2017 and could not find a facility where hygienic slaughtering took place. In most cases, refrigeration equipment was not available and where it was, it was poorly maintained and run down. Conditions may not be this extreme in other places in the world. In South Africa, I have been in abattoirs with very poor hygienic conditions, especially small facilities. How does one treat such meat to make it acceptable for further processing? Can anything be done?
The Case for Carcass and/or Primal Cut Washing and the Use of Organic Acids
Several researchers have found that integration of sanitizing methods, such as knife trimming in combination with other antimicrobial decontamination methods such as steam vacuuming, hot water and acid sprays systems and steam pasteurization can help to improve the microbial safety of carcasses after slaughter (Gorman et al 1995, Castillo et al, 1998, Castillo et al 1999, Pipek et al 2004).
“Medynsky, Pospiech, and Kniat (2000) found that an increase of the lactic acid concentration in meat above the level of 0.5% enhanced water holding capacity and reduced thermal loss. In another study, Jimenez-Villarreal et al (2003) found that lactic acid treatments on beef trimmings before grinding could improve or maintain the same sensory and instrumental colour, sensory odour, lipid oxidation, sensory taste, shear characteristics and cooking characteristics as traditionally processed ground beef patties. Therefore the use of these antimicrobial treatments could be used in industry as a measure of safety improvement without negatively impacting the fresh product. Carcass decontamination utilizing organic acids is a sanitation process that is widely used in the industry and has been studied deeply. In 1995 (Netten, Mossel and Veld, 1995), found that lactic acid decontamination was capable of eliminating salmonellae from pork, veal and beef carcasses and that this compound is also likely to be effective against C jejuni. This bacterium is at least 10-fold more sensitive to lactic acid than Salmonella. Furthermore, counts of C. jejuni on freshly slaughtered veal, pork, and beef carcasses are also up to l00-fold lower than those of Salmonella. Castillo et al., (1998) compared the effect of different decontamination interventions on E. coli O157:H7 inoculated on beef carcasses. Lactic acid rinses in combination with water wash, trimming and hot water reached reductions from 4.2 to 5.0 log CFU/cm2. Lactic acid is frequently used for beef carcass decontamination. Its ability to reduce pathogens or other organisms of faecal origin has been studied extensively showing that lactic acid has a strong antibacterial effect. Besides the antimicrobial effect, the studies reviewed show that the use of lactic acid as a meat sanitiser does not have a significant impact on sensory and/or physic-chemical characteristics.” (Rodriguez, 2004)
In light of these findings, I have used lactic acid and acetic acid spray to decontaminate carcasses, to reduce the total bacterial populations on the carcass surface. I have also used acetic acid, lactic acid and a combination of lactic acid and sodium bicarbonate which produce a sodium acetate solution for washing primals and trimmings that were exposed to questionable handling and storage conditions. All these measures have proved to be very effective. A typical reduction of as much as 90% (1 log10 cycle) can be expected from organic acid rinses. (Dickons, et al, 1996)
“The effectiveness of these acids will vary depending on the following:
- concentration (dosage),
- the application temperature,
- contact time,
- the amount of time spent spraying a carcass (it seems self-evident, but research clearly shows that the more time is spent on a carcass, the cleaner it will be)
- the water pressure,
- the distance of the hose nozzle from the carcass, especially if hot water is used because the closer the nozzle is to the carcass, less heat is lost as the water travels through the air.
- the sensitivity of the native microflora to the specific compound, and
- to a certain extent the design of the specific equipment.
CONCENTRATION
Organic acids are self-limiting due to discoloration of meat which occurs at or above the 3% concentration level.
PROCEDURE
The following procedures are suggested. “Wash only one carcass at a time. The worker needs to give each carcass the full attention that it needs and will reduce cross-contamination.
Distance from the hose nozzle to the carcass during spraying is important.
Use a gentle sweeping motion to apply the lactic acid to the entire carcass surface.
Work methodically from top to bottom to ensure that all carcass surfaces are treated with lactic acid.
Initially, a garden sprayer can be used. This type of sprayer is relatively inexpensive and simple to operate. In general, garden sprayers operate with a gentle flow rate. Use of this sprayer to thoroughly rinse a carcass may require extra time so that an adequate amount of 2% lactic acid is dispensed. Also, many of these garden sprayers are not equipped with a pressure gauge and require manual exertion to pressurize (unless retrofitted as described below).” (Flowers, 2006).
Temperature
“It is reported that in general, hot water is more effective at removing bacteria than warm or cold water. Hot water may discolour muscle tissue that is exposed on carcass surfaces. Therefore, consider using warm water if hot water is not used to wash carcasses. Washing carcasses with cold water do remove bacteria by physical force; yet, it does very little to injure or kill bacteria that may remain on carcass surfaces. This step is so counter-intuitive to meat processing staff that comparative studies must be done to validate the procedure.” (Antimicrobial Spray Treatment, 2005)
Pipek, et al, (2004) found that a warm spray was more effective even for a lactic acid spray. They found that it “is generally recommended to prefer warm solutions of lactic acid for the carcass decontamination. We tested the temperature decrease during the application and we were able to find that the drops of lactic acid solution at the moment when they fall on the carcass surface are up to 10 °C cooler than the original solution. We ascribe this temperature decrease partly to the heat exchange between drops and surrounding air and partly to evaporation of water from drops, which have a relatively high surface. Thus the temperature of drops of about 35−40 °C on the meat surface corresponds to the temperature of 45 °C of the original solution.” They showed that “the effect of lactic acid is higher, if its solution is warm (45 °C) in comparison with the cold solution (15 °C). The effect was higher with pork carcasses than with beef carcasses. In the case of the carcasses that were decontaminated with warm lactic acid solutions, the lag phases were prolonged by one day; during following days of cold storage, the differences decreased.” (Pipek, et al, 2004)
Pressure
“The water stream is most forceful at the opening of the hose nozzle. The water loses momentum the further it has to travel. As with temperature, it is a good idea to keep the nozzle no more than 30cm from the carcass surface. A Sanitizing Halso system will be developed for the future to replace the garden hose spray. It will be designed to deliver the lactic acid solution at a maximum pressure of 40 psi. FSIS has no current requirements concerning the minimum and maximum pressure for organic acids (i.e., lactic acid, acetic, and citric acid) when they are applied onto livestock carcasses. However, the rescinded FSIS Directive 6340.1—Acceptance and Monitoring of Pre-Evisceration Carcass Spray (PECS) Systems, dated 1/24/92, stated that the spray pressures should be limited to 50 psi.” (Antimicrobial Spray Treatment, 2005)
Time
“In general, research has demonstrated that the more time that is spent washing a carcass, the cleaner it will be. Washing the carcass for a longer period of time allows the force of the water to detach more bacteria and debris. It is suggested to start by allowing 60 seconds per carcass and to reduce this as equipment and operator experience improves to around 20 seconds per carcass.” (Antimicrobial Spray Treatment, 2005)
Suggestions for Establishing a Critical Limit for Food Safety Plan
Here are two ways to define a critical limit for this intervention, which may become a critical control point in the HACCP plan of a very small plant. Let’s assume lactic acid is used. Of course, the same will apply to any other organic acid.
1. “Specify the length of time (i.e., seconds or minutes) that the carcass will be sprayed with 2% lactic acid.
2. Specify the volume of 2% lactic acid that will be applied to each carcass.
Also, note that enough 2% lactic acid should be sprayed onto the carcass surface so that the whole surface is dripping wet and some of it runs off.” (Antimicrobial Spray Treatment, 2005)
Suggestions for Monitoring a Critical Limit
“Here are two feasible methods for monitoring the Critical Limits suggested above.
1. Use a titration kit to measure acidity (% acid) after preparing a solution of 2% lactic acid. Follow the manufacturer’s instructions closely to get a valid measurement. Record the acidity of each batch of 2% lactic acid solution on a record sheet.
2. During preparation of 2% lactic acid, measure and record the amounts (volume or weight) of water and lactic acid that are mixed. Mixing the correct amounts of concentrated acid and water will ensure proper preparation of 2% lactic acid.” (Antimicrobial Spray Treatment, 2005)
Sanitizing Halo System to be developed
Below I give a DIY system.
(Rodriguez, et al, 2004)
Unexpected Consequences
Pipek, et al, (2004) found unexpected benefits to their lactic acid carcass decontamination trials related to weight loss. They write, that “it was proved that the weight losses during cold storage were surprisingly lower in lactic acid-treated carcasses in comparison with control samples sprayed with water. The explanation for this effect can be found in changes in protein structure on the surface. The lactic acid treatment probably induces denaturation of the proteins on the surface and leads to pore closure; evaporation of water from the meat surface is reduced. The differences in weight losses between lactic acid-treated carcasses and controls were 0.6−1.0 % in the case of pork and 0.3−0.6 % in the case of beef carcasses. These differences are related to different tissues on the carcass surface. Whereas in beef carcass the muscle tissue prevails, the surface of pork half-carcass is covered by skin.” (Pipek, et al, 2004)
The Nigerian Experience
In Nigeria, we constructed a proper carcass wash area designed by Beyers Cronje.
We also installed an ECA system to treat our water and wash the carcasses down with anolyte water (ECA Generated Radical Water). The entire process is remarkably effective. We have similar results as reported by Pipek, et al, 2004, but I suspect it has to do with the fact that carcasses in Nigeria are received within hours of slaughter, and transported in mostly unrefrigerated trucks. This means that rigor mortis has not set in yet and the meat is effectively received still warm.
Let’s investigate anolyte wash and compare acid wash with anolyte wash. I give a breakdown based on general principles of meat science and chemistry, aiming to provide possible explanations of the results we observe.
Chemical Processes in Warm Carcasses Pre-Rigor Mortis
Upon slaughter, animal carcasses undergo a series of biochemical changes leading to rigour mortis, the stiffening of muscles post-mortem. Before rigour mortis, the muscle is in a state where it can still absorb water due to the integrity of cell membranes and the active physiological state of the muscle tissues.
-> Anolyte Water Treatment: Anolyte water, produced through Electro-Chemical Activation (ECA) systems, is known for its sanitizing properties, largely due to its content of hypochlorous acid (HOCl). When applied to warm carcasses, the water absorption we are observing could be attributed to several factors:
- Osmotic Balance: Muscle cells might absorb water to maintain osmotic balance, especially if the anolyte solution is hypotonic compared to the cells.
- Protein Solubility: The pH of the anolyte water can affect protein solubility in the muscle, potentially increasing water-binding capacity if conditions favour protein hydration.
-> Affinity for Water Retention: This can be explained by the water-holding capacity of muscle proteins, particularly myofibrillar proteins, which can bind water through both capillary forces and hydrophilic interactions.
Impact of Organic Acid Use
Using organic acids (e.g., lactic acid, acetic acid) on carcasses is a common practice for microbial decontamination and pH reduction on the meat surface.
- Water Absorption: The application of organic acids may lead to a superficial denaturation of proteins on the meat surface, which could temporarily increase the surface’s water-holding capacity due to changes in protein conformation.
- Pore Closing and Protein Denaturation: The hypothesis by Pipik et al. (2004), suggesting that organic acids can cause pore closing by denaturing surface proteins, aligns with the understanding that acid-induced denaturation can alter meat surface characteristics, potentially reducing water loss during subsequent chilling by creating a less permeable surface layer.
- The extent of absorption and the subsequent impact on weight loss during chilling could differ due to protein denaturation at the surface, which may limit further water retention and enhance moisture loss prevention.
Conclusion
What is the difference between a large and a very small abattoir? The scale is the number of animals slaughtered per day, but this will make micro and food quality a bigger challenge in large plants. The biggest difference is in the equipment. Small plants don’t have access to the right equipment that makes very hygienic slaughtering possible. Many plants have the right equipment, but their procedures and practices lack training and discipline. (By contrast, I have found very small abattoirs in New Zealand with an unexpected level of sophistication and very clever design which enables them to produce meat on par with some of the biggest abattoirs in the world.) Even though it is reported that between 1500 and 2000 heads of cattle are being slaughtered at one abattoir in West Africa, they have no proper equipment and where they have it, the plant is not run as a single organism with proper management or procedures. Everything that is said about very small abattoirs applies to them. There is a place for carcass decontamination to prepare meat for processing.
References:
Antimicrobial Spray Treatments for Red Meat Carcasses Processed in Very Small Meat Establishments (2005) Prepared by Department of Food Science, The Pennsylvania State University, Department of Animal Science and Food Technology, Texas Tech University Department of Food Science and Nutrition, Washington State University. 2005
Dickons, J. S., Hardin, M. D., and Acuff, G. R.. Microbial Inactivation Methods, Organic Acid Rinses. (1996) Microbial Inactivation methods, American Meat Science Association, 49th Annual Reciprocal Meat Conference.
Flowers, S. L.. 2006. Identification and Validation of Antimicrobial Interventions for Red Meat Carcasses Processed in Very Small Establishments The Pennsylvania State University, The Graduate School, College of Agricultural Sciences.
Lawrie, R. A., & Ledward, D. A. (2006). “Lawrie’s Meat Science.” Woodhead Publishing. This book provides a comprehensive overview of the biochemical and physical changes in meat post-mortem, including water-holding capacity and the effects of various treatments on meat quality.
Meat Inspectors Manual for Abattoir Hygiene, published by the Directorate of Veterinary Services at the South African Department of Agriculture (2007)
Pipek, P., FÍLA, P. JELENÍ-KOVÁ, J., BRYCHTA, J and MIYAHARA, M.. 2004. Technological Aspects of Acid Decontamination of Carcasses Chem. Listy 98, 865 − 869 (2004)
Rodriguez, G., Acuff, G. R., and Castillo, A.. 2004. Development of a Carcass Sanitizing Spraying System for Small and Very Small Slaughterhouses. Final Report to FSIS/TPDS Department of Animal Science Texas A&M University College Station, TX 77843-2471 October 2004.
Toldrá, F. (Ed.). (2010). “Handbook of Meat Processing.” Wiley-Blackwell. This handbook includes discussions on the use of various interventions, including water and organic acids, for improving meat safety and quality.