Old World Tradition Meets New World Expertise.
Shelf Stable Meat Products
Jay B. Wenther, Ph.D
American Association of Meat Processors
One of the oldest forms of meat preservation is represented by the product category currently known as shelf-stable meat products. Historically, the development of dry and semi-dry sausage technology was discovered several thousand years ago. Simply stated, the application of salt on meat (whole pieces or cut up) and the process of drying were found to preserve meat for months under normal climatic conditions.
For many years in the United States, the moisture: protein ratio(MPR) was used to define the shelf stability of meat products. This is no longer the case and moisture: protein ratios are only to be used to define the standard of identity of meat products. The United States Department of Agriculture’s Food Standards (USDA) and Labeling Policy Book (USDA 2003) defines the MPR of certain products. These MPR are listed in Table 1. The regulations published in the Food Standards and Labeling Policy Book are for labeling purposes only! The MPR that is referred to is related to product characteristic that is expected by the consumers.
Table 1: Moisture Protein Ratio (MPR) of some common meat products.
Jerky • 0.75:1
Pepperoni • 1.6:1
Dry Sausage • 1.9:1
Italian Salami • 1.9:1
Kippered Beef • 2.03:1
Dried Meat • 2.04:1
Chipped Beef • 2.04:1
Genoa Salami • 2.3:1
Thuringer • 3.7:1
A moisture protein ratio refers to the quantity of moisture in a product in relationship to the quantity of meat protein, expressed as X parts (or percent) of moisture for each part (or percent) of meat protein. In the United States we base the degree of drying on MPR as opposed to Europe where water activity(Aw) is used.
In order to achieve shelf stability for food safety purposes, certain intrinsic parameters must be achieved. These parameters consist of either water activity and/or pH.
Water activity is defined by the ratio of the water vapor pressure of food substrate to the vapor pressure of pure water at the same temperature. In other words, water activity refers to the available water in a product upon which microorganisms depend on for growth. The preservation of foods by drying is a direct consequence of removel or binding of moisture, without which microorganisms do not grow.
To get a better idea of water activity, the water activity of some common foods can be observed in Table 2.
Table 2: Water activity of some common foods.
Water • 1.0
Fresh Meat • .95-1.0
Bread • .94-.97
Cured Meat • .87-.95
Flour • .67-.80
Cerals • .10-.20
Sugar • .10
A meat product with a water activity of less than 0.85 is usually considered shelf stable and would not support the growth of pathogenic microorganisms. A water activity of ≤0.85 has been common for the control of S.aureus. The new (2004) FSIS Compliance Guidelines suggested water activity critical limit for stabilization of jerky is ≤0.70 for product in contact with air, which is low enough to exclude mold growth.
The term Ph is related to the acidity of the product. In scientific terms, p(potential of) H(hydrogen) or pH is the negative log of the hydrogen-ion concentration in gram atoms per liter. The pH scale values range from 0 to 14. A neutral soluttion has a ph of 7. A pH less than 7 indicates an acidic solution while a pH greater than 7 indicates an alkaline (basic) solution.
To get a better idea of pH, the pH of some common foods can be observed in Table 3.
Table 3: The pH of some common foods.
Limes • 1.8-2.0
Apples • 2.9-3.3
Summer Sausage • 4.3-5.0
Watermelon • 5.2-5.6
Ground Beef • 5.1-6.2
Chicken • 6.2-6.4
Milk • 6.3-6.5
Sweet Corn • 7.3
A reduction in pH can be achieved through the use of starter cultures (e.g. lactic acid) or acidulants (i.e. encapsulated citric acid, encapsulated lactic acid, etc.).
Traditional fermentation relied on indigenous microorganisms that were present on the meat ingredients, the spices, or the environment. Starter cultures evolved in which meat processors can use specific species of microorganisms to achieve a desired flavor profile. The starter cultures help improve the safety of the meat products as well as improve the consistency of the flavor and texture. The starter cultures depend on a food source (i.e. dextrose) to live and grow. As the microorganisms eat the dextrose they excrete lactic acid, giving the final product the traditional “tangy” flavor profile.
Starter cultures require a specific environment to work. The goal of the fermentation stage is to provide optimum conditions of temperature, humidity, and time for the lactic acid producing bacteria to grow. The conditions need to be favorable to the starter culture and you should follow the culture suppliers recommendations.
The encapsulated acids use naturally occurring acids that are encapsulated with a hydrogenated vegetable oil, which melts at 135°F. The coating allows the use of the acid for the production of a tangy flavor profile in dry and semi-dry meat products. If the acid were not coated, it would denature the proteins and not allow the proteins to properly bind to each other prior to thermal processing. Encapsulated acids greatly reduce the time it takes to produce “tangy” products.
Due to today’s microbiological concerns, particularly E. coli O157:H7, Salmonella, and Listeria monocytogenes, meat processors must realize how they can control the growth of certain pathogens. Since the implementation of HACCP, meat processors must also justify why certain critical limits were chosen for critical control points with “scientific documentation.”
USDA, 2003. United States Department of Agriculture Food Standards and Labeling Policy Book. Washington, D.C.