Meat of a healthy animal is clean and contains very few bacteria. Any invading bacteria will be destroyed by the animal’s immune system. Once the animal is slaughtered these defense mechanisms are destroyed and the meat tissue is subjected to rapid decay. Although unaware of the process, early sausage makers knew that once the animal was killed, it was a race between external preservation techniques and the decomposition of the raw meat to decide the ultimate fate of the issue.
Most bacteria are present on the skin and in the intestines. In stressed animal bacteria are able to travel from the animal’s gut right through the casing into the meat. The slaughtering process starts introducing bacteria into the exposed surfaces. Given time they will find their way inside anyhow, but the real trouble starts when we create a new surface cut with a knife. This creates an opening for bacteria to enter the meat from the outside and start spoiling it. We must realize that they don’t appear in some magical way inside of the meat, they always start from the outside and they work their way in.
In a large piece of meat the outside surface serves as a natural barrier preventing access to bacteria. They have a long distance to travel to reach the center of the meat. Meat muscles are surrounded with a connective tissue which also acts as a protective sheath and so does the outside skin. Duties like cutting meat, grinding, mixing or stuffing all increase meat temperature and should be performed in the kitchen at the lowest possible temperatures as fast as possible. Otherwise we create conditions for the growth of bacteria and that will decrease the shelf life of the product.
Food safety is nothing else but the control of bacteria and to do it effectively first we have to learn how bacteria behave. Once one knows what bacteria like or dislike, it will be very simple to produce safe products with a long shelf life. Let’s make something clear: it is impossible to eliminate bacteria altogether, life on the planet will come to a halt. They are everywhere: on the floor, on walls, in the air, on our hands and all they need to grow is moisture, nutrients and warm temperature. Given ideal conditions bacteria can double up in numbers every 20 minutes. In a refrigerator their number will also grow slower, but they can still double up in 12 hours. At room temperatures bacteria will grow anywhere they have access to nutrients and moisture. Short of deep freezing, it is impossible to prevent bacteria from spoiling meat, all we can do is to create conditions that will slow down their growing rate. The following three factors allow us to control the growth of bacteria and directly influence the safety of meat products:
- Water activity (Aw)
- Meat acidity (pH)
Storing and processing the freshest meat at low temperatures is the strongest weapon that we have to fight bacteria. Additional factors such as adding salt, nitrite, increasing meat’s acidity, eliminating moisture, vacuum packing and others are additional safety measures that help to produce a safe product with the maximum shelf life. Nevertheless the single most important factor is using the lowest practical temperatures for processing and storing meat. When you answer the telephone and leave ground meat on the kitchen table for 3 hours it will not matter much, as long as you only make one or two pounds of sausage. It will be consumed in a day or two and there will not be enough time for the meat to go bad. But if you buy a 50 lbs box of pork butts to make different sausages for your family at Christmas, now it is a different matter. You cannot eat all that meat in a day or two. Some of it will hang in the kitchen, some will be in a refrigerator, a good half will go into the freezer. It is in your own interest to have those sausages last as long as possible and now all those low temperatures and good manufacturing techniques will come into play.
Effects of Time and Temperature on Bacteria Growth
Under the correct conditions, spoilage bacteria reproduce rapidly and the populations can grow very large. Temperature and time are the factors that affect bacterial growth the most. Below 45° F bacteria grow slowly and at temperatures above 140° F they start to die. In the so called “danger zone” between 40-140° F (4-60° C) many bacteria grow very well. Most bacteria will grow exponentially at temperatures between 70° F and 120° F. When bacteria grow, they increase in numbers, not in size. Let’s see how fast bacteria grow at ideal temperature:
|Number of bacteria||Elapsed time|
|160||1 hour 20 min|
|320||1 hour 40 min|
|1280||2 hours 20 min|
|2560||2 hours 40 min|
|10,240||3 hrs 20 min|
|20,480||3 hrs 40 min|
|81,920||4 hrs 20 min|
|163,840||4 hrs 40 min|
|655,360||5 hrs 20 min|
|1,310,720||5 hrs 40 min|
Now it becomes evident what happens to a piece of meat left out on the kitchen table for many hours on a beautiful and hot summer day. The thermometer drawing that follows below has been compiled from the data we found at the College of Agriculture, Auburn University, Alabama. It shows the time that is required for one bacteria cell to become two at different storage temperatures. Looking at the drawing we can see that once the temperature rises above 50° F (10° C), bacteria will double up every time we raise the temperature by about 5° F. From the above examples we can draw a logical conclusion that if we want to process meats we should perform these tasks at temperatures not higher than 50° F (10° C). And those are the temperatures present in meat processing plants. You might say that lowering the temperature of the room will be better still. Of course it will be better, but people working in such conditions for 8 hours a day will find it very uncomfortable.
Bacteria growth with temperature.
It can be seen that at 32° F (0° C) bacteria needs as much as 38 hours to divide in two. That also means that if our piece of meat had a certain amount of bacteria on its surface, after 38 hours of lying in a refrigerator the amount of bacteria in the same piece of meat will double. If we move this meat from the refrigerator to a room having a temperature of 80° F (26.5° C) the bacteria will double up every hour (12 times faster). At 90° F (32° C) they will be dividing every 30 minutes.
After cooking, meats are free of bacteria, but leaving them warm for an extended time will invite new bacteria to settle in and start growing. For this reason smoked and subsequently cooked meats are submitted to cold showers to pass through the “danger zone” as fast as possible.
Major meat poisoning organisms
|Salmonella||Food borne infection|
|E. coli (enteropathogenic type)||Food borne infection|
|Listeria monocytogenes||Food borne infection|
|Campylobacter jejuni||Food borne infection|
|Yersinia enterolytica||Food borne infection|
|Staphylococcus aureus||Food borne intoxication|
|Clostridium botulinum||Food borne intoxication|
|Mycotoxin producing moulds||Food borne intoxication|
|Norovirus||Food borne infection|
Temperature Limits for Food borne Bacteria in Raw Meat
|Growth temperatures||Time at test temperatures|
|Bacillus cereus||41°F||41°F||8.3 hr|
|Clostridium botulinum nonproteolytic||37.9°F|
|Clostridium botulinum proteolytic||50°F|
|Clostridium perfringens||53.6°F||53.6°F||11.5 hr|
|Escherichia coli SF||44.6°F||46.8°F||40 hr||6.9 hr|
|E. coli O157:H7||35.6°F||no growth|
|E. coli O157:H7, pH 5.7||53.6°F||16.2 hr||6.0 hr|
|E. coli O157:H7, pH 6.3||53.6°F||2.78 hr||3.9 hr|
|Listeria monocytogenes||32°F||39.2°F||22.8 hr|
|Listeria monocytogenes||39.2°F||9.3 hr|
|Salmonella typhimurium||41°F||50°F||45 hr||9.65 hr|
|Yersinia enterocolitica||30.2°F||41°F||16.53 hr|
|Yersinia enterocolitica||50°F||12.73 hr|
REFRIGERATED TRANSPORTATION & HANDLING OF CARCASSES AND MEAT
Refrigeration of carcasses
Carcasses should go into the cooler as soon as possible and should be as dry as possible. The object of refrigeration is to retard bacterial growth and extend the shelf-life. Chilling meat post-mortem from 40°C down to 0°C and keeping it cold will give a shelf-life of up to three weeks, provided high standards of hygiene were observed during slaughter and dressing.
Carcasses must be placed in the cooler immediately after weighing. They must hang on rails and never touch the floor. After several hours the outside of a carcass will feel cool to the touch, but the important temperature is that deep inside the carcass. This must be measured with a probe thermometer (not glass), and used as a guide to the efficiency of the cooling.
A. Sheep carcasses in the chill-room, hung on rails clear of the floor and spaced to allow air circulation to speed drying
The rate of cooling at the deepest point will vary according to many factors including the efficiency of the cooler, the load, carcass size and fatness. As a general guide a deep muscle temperature of 6–7° C should be achieved in 28 to 36 hours for beef, 12 to 16 hours for pigs and 24 to 30 hours for sheep carcasses. Failure to bring down the internal temperature quickly will result in rapid multiplication of bacteria deep in the meat resulting in off-odours and bone-taint.
High air speeds are needed for rapid cooling but these will lead to increased weight losses due to evaporation unless the relative humidity (RH) is also high. However, if the air is near to saturation point (100 percent RH) then condensation will occur on the carcass surface, favouring mould and bacteria growth. A compromise between the two problems seems to be an RH of about 90 percent with an air speed of about 0.5 m/second. Condensation will also occur if warm carcasses are put in a cooler partially filled with cold carcasses.
The cooler should not be overloaded beyond the maximum load specified by the manufacturers and spaces should be left between carcasses for the cold air to circulate. Otherwise cooling will be inefficient and the carcass surface will remain wet, favouring rapid bacterial growth forming slime.
Once filled, a cooler should be closed and the door opened as little as possible to avoid sudden rises in temperature. When emptied, it should be thoroughly washed before refilling. Personnel handling carcasses during loading and unloading operations should follow the strictest rules regarding their personal hygiene and clothing and should handle carcasses as little as possible.
Meat under refrigeration
Chilled meat must be kept cold until it is sold or cooked. If the cold chain is broken, condensation forms and microbes grow rapidly. The same rules about not overloading, leaving space for air circulation, opening doors as little as possible and observing the highest hygiene standards when handling the meat apply. An ideal storage temperature for fresh meat is just above its freezing point, which is about – 1°C (- 3°C for bacon because of the presence of salt). The expected storage life given by the International Institute of Refrigeration of various types of meat held at these temperatures is as follows:
|Type of meat||Expected storage life at – 1°C|
|Beef||up to 3 weeks (4–5 with strict hygiene)|
|Edible offal||7 days|
|Bacon||4 weeks (at – 3°C)|
Under commercial conditions, meat temperatures are rarely kept at – 1°C to 0°C, so actual storage times are less than expected. The times would also be reduced if RH were greater than 90 percent.
Meat should be placed in the refrigerator immediately following receipt. Any parts which show signs of mould growth or bacterial slime should be trimmed off and destroyed. Hands must be thoroughly washed after handling such trimmings and knives must be sterilized in boiling water. The refrigerator should be thoroughly cleaned after finding such meat and should also be cleaned on a regular basis.
Carcasses, quarters and large primals should not be cut into smaller portions before it is necessary as this will expose a greater surface area for bacteria to grow. Freshly cut surfaces are moist and provide a better medium for bacterial growth than the desiccated outer surfaces of cuts that have been stored for some time.
An accurate thermometer should be placed in the refrigerator and checked regularly. The temperature should remain within a narrow range (0° to + 1°C).
Transport of meat
Vehicles for transporting meat and carcasses should be considered as an extension of the refrigerated storage. The object must be to maintain the meat temperature at or near 0°C. Meat should be chilled to 0°C before loading. Meat should hang on rails, not on the floor. If stockinettes are put on carcasses they must be clean. Meat trucks should not carry anything other than meat.
The refrigeration is usually produced by injecting liquid nitrogen or carbon dioxide (CO2) into the compartment or by blowing air over CO2 chunks (dry ice). The temperature in these vans can be set and controlled to minimize the temperature rise and to avoid condensation on the meat surface.
Insulated vans without refrigeration may be refrigerated by adding dry ice. While this is a reasonably good alternative to the refrigerated truck it does not allow the temperature to be controlled.
Uninsulated vans and open trucks should not be considered as suitable transport for meat, particularly in hot climates. In addition to the temperature abuse, condensation will occur when the meat goes back into refrigeration, and in open trucks the meat is exposed to attack from insects. Loading and unloading should be done quickly. If there are any unavoidable delays then dry-ice blocks should be placed in the partly filled van.
Insulated trucks/vans with refrigeration units should be used for transporting meat
How important is refrigeration for meat?
Where refrigeration is unavailable either owing to financial or technical reasons (e.g. no power supply), the shelf-life of meat is reduced to days or hours, not weeks. Slaughter and dressing must be near the point of sale and it must be quick and clean. If carcasses and meat are kept in well-insulated rooms, the temperature can be reduced with dry-ice blocks, if these are available. Since it is easier to chill boneless cuts rather than whole carcasses, hot-boning should be considered.
Stock must be handled carefully to avoid producing high-pH meat which will spoil more quickly. Rooms used for slaughter and handling meat must be clean and well ventilated, but out of direct sunlight, dust-free and vermin free (rodents and insects). Hot water (82°C) must be available to clean all equipment and surfaces and personnel must work very hygienically. Receive all blood into sealed containers and have separate skips on wheels for hooves, skins, green offal and trimmings.
Processing and packing of offal must be done in a room separated from the slaughter hall or other meat-handling facilities
Dressing on a vertical hoist will minimize contamination by floor or cradle contact. Let nothing drop on the floor, only into skips. Personal hygiene must be scrupulous. Any spills of gut contents on to the meat should be cut off, but careful work will avoid this. The dressed carcass should be hung on rails. If beef is quartered to facilitate handling, the cut surface is at risk.
Red offal should be hung on hooks. Any offal processing must be in rooms away from meat-handling facilities. Intestines for human consumption must be thoroughly cleaned and washed.
Meat should be put on sale within a day of slaughter. Transport of non-refrigerated meat is very hazardous. If meat is to be put in stockinettes and sacks these must be very clean. Meat should be on rails in the truck or wagon, and it is not advisable to carry it more than a day’s journey before sale.
The abundant growth and opportunity capitalization in the Indian meat Industry solely relies on the Safety of meat production and distribution. The very backbone of the same remains in the hands of sufficient and effective Cold Chain equipments. Encouragement of Food Safety authorities on strict implementation of Food Safety standards and effective Cold Chain Equipments would pave a way for Indian meat manufacturing companies to implement Global Best Practices on meat production and handling. Cold Chain in Indian Meat sector still remains at very nascent stage and we still dream of finding the right road to progressive Cold chain practices to enable Indian players in Meat to reaching global standards.
By Divya V Amrith, Director – Marketing & Strategy , Transfreez Mobile Refrigeration