By: Lynn Knipe
Meat Export Research Center
Iowa State University

The production of sectioned and formed meat products has become increasingly more popular in the poultry and red meat industries. These products have gained consumer acceptance and are manufactured by processes which are inherently advantageous to processors. Sectioned and formed (S/F) products are made by mechanically working meat pieces to disrupt the normal muscle cell structure. This produces a creamy, tacky protein exudate on the surface of the meat pieces. This exudate binds the meat pieces when heated to produce a cohesive, formed product of improved quality and cooked yield while maintaining the texture and appearance of intact muscle. The mechanical action of tumbling and massaging primarily affects external tissues to produce the surface exudate. Some internal tissue disruption is also likely, which explains the enhanced tenderness, pickle penetration and distribution, and water-holding capacity.

The mechanical action required to produce high quality S/F meat products may be achieved in a variety of ways, but most commonly involves the processes of tumbling and/or massaging. The physical treatment applied by tumbling and massaging differs. In the case of massaging, frictional energy is generated from pieces being rubbed and massaged against each other by rotating paddles. There are basically two types of massagers: one with horizontal paddles and the other with vertical paddles. The vertical paddles cause less damage to meat (and/or bone) and are reported to give a better, faster massage treatment. A massager should have reversible direction paddles. This helps to prevent immobilization of meat pieces in the corners of the massaging vat and frees pieces that are caught on the paddles. Furthermore, a variable speed drive would allow one to vary massage speed in an attempt to find the optimal treatment for each product.

Tumbling, on the other hand, is a more rigorous physical treatment and involves the impact energy from forcing meat pieces to fall from the top of a rotating drum. It has been suggested that the meat needs to drop at least three feet in a rotating tumbler to get the maximum effect. The rigorous tumbling action causes foaming of the exudate which suggests the need for vacuumizing the tumbler contents. There are also two basic types of tumblers: the rotating drum and the end-over-end tumbler. The rotating drum is more gentle in treatment and uses less space per volume of capacity.

While massaging has been more widely accepted in the United States, the use of vacuum tumbling is becoming increasingly more popular. The advantages of vacuum tumbling will be discussed later in more detail.

An alternative to tumbling and massaging is mixing. However, mixers can be very destructive to meat pieces and should be used only on small pieces for relatively short time periods.

Macerating or tenderizing procedures may be applied in addition to or in place of conventional multiple stitch brine injection to facilitate brine distribution, to increase protein exudate formation by increasing muscle cell disruption, and to further soften muscles to enhance ease of stuffing.

Due to the wide variety of equipment being used in making sectioned and formed meat products, it might be best to refer to the overall process as mechanical conditioning.

The main idea is to apply a physical treatment which produces sufficient protein exudate and which allows for adequate cure migration without causing extensive physical damage to the meat. The mechanical action of tumbling/massaging is a time-work intensity relationship. The length of time required depends upon the intensity of the physical treatment imparted to the pieces of meat. To an extent, the more intense the mechanical working, the less time required. This mechanical conditioning raises the temperature of the meat, which could indicate the degree of mechanical working. One must be careful not to overwork the meat as this will result in a dry product which is more difficult to stuff.

Many different theories exist concerning the length of the tumbling/massaging treatments. While massaging action is less destructive to the meat, the resultant protein extraction is also slower than with tumbling. Research has indicated that from 4-8 hours to as long as 20 hours of continuous massaging may be required to produce a product of acceptable bind.

There is much less agreement between processors and equipment manufacturers on the tumbling treatment cycles and duration. Many believe a much shorter tumbling treatment is adequate to produce a desirable product. Shorter tumbling treatments may be sufficient for an acceptable bind but longer treatments may be necessary to obtain any significant yield and quality advantage. The use of vacuum further decreases the tumbling time required to produce a good bind by preventing the production of foam. Periodic rest periods within the tumbling treatment are important to allow time for adequate cure migration while preventing excessive muscle destruction which could result from a continuous process and may allow for dissipation of foam in the exudate in the case on non-vacuum tumblers.

An alternative approach to the periodic rest periods of massagers and tumblers would be to tumble or mix continuously for 1 to 2 hours, followed by a rest period of 18 to 24 hours in a separate combo bin, ending with a final mixing until sufficient exudate is produced. This concept may give sufficient mechanical action, while allowing adequate time for distribution and action of brine ingredients without tying up tumblers and mixers for long periods of time.

One must keep in mind that cycle and total treatment times will vary among pieces of equipment so every processor needs to experiment with the equipment available to determine an optimum processing cycle for the desired product.

The advantage of greatest interest to most processors is the increased cooked yield and decreased shrink of the final product. The disruption of internal tissues due to the mechanical action of tumbling, massaging, etc., combined with the addition of salt (NaCl) and alkaline phosphates (most commonly a 90/10 mixture of tripoly- and hexametaphosphates), causes increased protein solubilization. Solubilized proteins in the meat tissues enhance water absorption prior to heat processing. Upon heating, the gel formed by the solubilized proteins holds additional water and decreases cooking loss. In the industry, processors report that tumbling decreases cooking shrink 2 to 3 percent, which agrees closely with the findings of this author. Many equipment manufacturers claim that massaging increases yield by at least 4 percent. Since the amount of added moisture is regulated for S/F meat products, the most significant effect of reduced cooking loss is the reduction in injection levels which results in more easily achieving desired pump level.

Secondly, mechanical conditioning greatly enhances sliceability or cohesiveness of muscle pieces within a sectioned and formed product. This allows for smaller, lower value meat pieces to be bound together to produce a more appealing and saleable final product. The binding ability of meat pieces will be discussed later.

Additionally, S/F products are desirable to today's consumers because they are adaptable to any size family unit, are lean, and tender, are convenient to heat in microwave ovens and are a more desirable meat item for today's consumers to work with (no gelatin, strings, or bones and less connective tissue and fat).

Another advantage is the uniform weight and shape of sliced S/F products. This allows for better control of portion size and weight. Ham, turkey and beef rolls have become very popular in the institutional food service as well as the retail market place. In addition, this product can be formed in the shape of cuts such as pork chops, ham steaks, various beef steaks, etc.

Improved pickle penetration also reduces curing time to under 24 hours as compared to the 3-7 days normally considered necessary to obtain uniform cure distribution by conventional stitch pump curing, especially in the case of dark, firm and dry (D.F.D.) hams. This results in a higher turnover rate in inventory.

Furthermore, improved pickle penetration causes a better, more uniform cured color. It has been observed that mechanical working causes a lightening of the cured meat color. Vacuum during mechanical conditioning reduces the exposure of lean tissue to oxygen which results in a brighter, more stable cured color and eliminates air pockets in formed products.

Also, there is the advantage of more complete and efficient use of available raw meat materials. Imagination is the only limitation to the wide variety of raw meat materials that can be incorporated into S/F products. Some examples: the use of high quality fresh meat trim for HRI processing; the addition of ground or emulsified, cured shank meat to hams during mechanical conditioning (see labeling discussion); the use of whole hams with bruises or broken bones removed; the use of heavier primal cuts, which without mechanical conditioning would tend to be tough; the use of meat from poultry carcasses to produce a boneless product of more desirable shape and size; the sectioning of sow loins of various sizes to produce products of less bone and fat and of more desirable and uniform shape; and the use of soy isolates and similar extenders to produce "combination hams".

Mechanically conditioned meat also displays the advantage of greater ease in stuffing. Due to the temporary softening effect of the mechanical action on the meat, it is easier to pump product, and to completely fill casings or molds of any shape to predetermined weights while eliminating undesirable voids between pieces.

Mechanical conditioning has also been found to increase tenderness of cured meats. This is due to the disruption of cellular connective tissue and increased moisture retention upon cooking. This tenderizing effect can be applied to heavier primal cuts to produce a more desirable product.

Finally, mechanical conditioning has even been credited with improving the flavor and aroma of the final product. This is best explained by reduced drip loss which could contain water soluble flavor compounds and to the improved distribution of nitrite and alkaline phosphates. Nitrite and phosphates are both credited with antioxidant properties.

A major disadvantage to mechanical conditioning is the initial cost of equipment. The equipment is relatively expensive and one batch may occupy one unit for 18 to 24 hours. While the actual expenditures for an individual tumbler is much greater than for a massager, the greater capacity per tumbler can generally make it the more favorable option. An alternative to commercial massagers might be to make your own paddle-motor units and set these on existing stainless steel combo bins. Also, as mentioned before, vacuum mixers could substitute for tumblers and massagers.

Another disadvantage is the labor required for boning, skinning, trimming and sorting. The extent of this disadvantage depends upon the desired quality of a product. This process does not work miracles. Fat and connective tissue particularly, and multi-color muscles to a lesser extent, can greatly decrease visual attractiveness and aesthetic value of the product. The highest quality products demand the time of skilled labor to remove silver skin, as much external and seam fat as possible, and (in the case of ham) the sorting of muscles by color.

Finally, the procedure may not work optimally and/or may even cause excessive muscle destruction if the treatment time and intensity are not carefully monitored. Excessive mechanical conditioning could yield a softer, yet chewier finished product, while mechanical conditioning cycles that are too short could result in a dense, dry product which lacks uniformity of pickle distribution.

An important purpose of tumbling and massaging is to solubilize and extract myofibrillar proteins to produce a protein exudate on the surface of the meat. This exudate binds the formed pieces together upon heating. At the salt levels commonly used in curing meats it is primarily the rnyofibrillar proteins, especially myosin, that act to bind meat pieces. The results of tumbling and massaging are not produced by the mechanical treatment alone, but with the addition of salt and alkaline phosphates.

Salt, when added alone to meat, increases the amount of water absorbed by proteins when muscle is at or above pH 6 by decreasing the isoelectric point. This causes a spreading of muscle cell components due to electrostatic repulsion, which allows more water to be bound or trapped within the muscle fibers or cells, reducing fluid loss upon cooking.

Salt, however, has been shown to have the least effect (as compared to phosphates and massaging) on relative percentages of myofibrillar proteins in the exudate. Myosin is easily extracted by salt solutions (up to 3 percent by weight) in pre-rigor muscle but is not split from the post-rigor or actomyosin complex by salt alone. The addition of salt alone to massaged ham yields predominantly fragmented fibers in the surface exudate.

The addition of phosphates seems to be primarily responsible for the solubilization of myofibrillar proteins in post-rigor muscle. The addition of alkaline phosphates has been shown to have the greatest single effect on the relative percentages of myofibrillar proteins in the exudate of massaged hams. Alkaline phosphates aid in the solubilization of proteins even without salt, yet salt and massaging enhance this solubilization of proteins. Furthermore, alkaline phosphates significantly reduce cooked losses when added to massaged hams.

The action of phosphates in meat can be explained in several ways. First, phosphates may affect the water-holding capacity of post-rigor muscle by increasing the pH of the muscle, which increases the net negative charge on muscle. These negative charges increase the electrostatic repulsion between fibers and ultimately increases the hydration of the muscle. Most of the food grade phosphates examined by this author raise the pH of meat, yet the relationship between their effect on pH and water-holding capacity varies with the different phosphates.

Secondly, phosphates act as electrolytes and increase ionic strength of the meat system. The phosphate anions can enhance meat hydration directly by increasing the number of binding sites for water. By increasing the ionic strength, phosphates increase the net negative charge on proteins. This causes a repulsion of adjacent molecules which increases hydration. However, at the levels of phosphate normally used the ionic strength may not be increased enough to be a big influence.

Furthermore, tetrasodium pyrophosphate can dissociate the actomyosin complex into actin and myosin. As mentioned previously, actin and myosin, individually, are easier to solubilize at the salt levels used in most cured products than the actomyosin complex. Therefore, adding the pyrophosphate form directly should produce a high quality exudate more quickly than tripolyphosphates, as the tripolyphosphates need some time to be enzymatically hydrolyzed to the pyrophosphate form. However, tetrasodium phyrophosphates are much less soluble than tripolyphosphate at normal pickle temperatures.

Finally, phosphates bind or "tie up" bivalent cations (such as Ca positive, Mg positive, Fe postive, etc.) from hard water supplies and in meat which further enhances water-holding capacity of the meat. Tying up cations also inhibits oxidative rancidity and slows the rate of color fading of cured meat.

However, it is the synergistic effect of salt combined with alkaline phosphates which improves yields and maximizes myofibrillar protein solubilization. At the levels of salt and phosphate used in the production of sectioned and formed meat products, the salt concentration increases ionic strength enough to spread the filaments but does not cleave the crossbridges, while phosphates resolve the actomyosin structure but may not increase ionic strength enough to spread the filaments.

Keeping within the practical ranges of ingredient use, a maximum bind is produced with the addition of a pickle that produces a final product that contains 2 to 3 percent salt and 0.3 percent to 0.5 percent phosphate (usually a mixture of tripoly and hexametaphosphates). If any salt is to be added to the product at all, a minimum of 0.6 percent in the final product may be necessary. Below 0.6 percent salt in the final product has been shown to actually be more detrimental to the product than no added salt. Excessive salt may decrease bind despite the extraction of sufficient protein.

Binding of muscle pieces during the heat treatment (to l55 degrees F or 68 degrees C) is very important to the quality of a sectioned and formed product and is affected by several factors in addition to the presence of salt and polyphosphates.

The binding of meat pieces is also affected by the pH of the muscle. Heat initiated binding of muscle pieces is improved with higher pH�s. Myosin is optimally solubilized at pH 6.5.

Binding strength is also affected by the contractile state of the meat. Increased degree of contraction in the muscle will decrease the solubility and extractability of proteins. The use of pre-rigor muscle greatly increases bind values over post-rigor muscle. This is supported by the fact that more crude myosin is extracted from pre-rigor muscle than from post-rigor muscle and that myosin when compared to all other muscle proteins has the greatest positive effect on protein binding when cooked. In addition, using pre-rigor meat can increase cooked yields and decreacre time and energy use of heat processing.

Binding strength also increases with increased massaging or blending time. This is due to increased exudate formation on the surface of the meat. Crude myosin extraction is increased with increased blending time, but the binding ability of the crude myosin extracted has been reported to decrease with increased blending time. Myosin has been found to lose its solubility with time, yet it has also been observed that an acceptable product can be made when the mechanically worked product is refrigerated for a day or two or frozen for long periods of time prior to thermal processing.

Binding strength is also increased with decreasing meat particle size. More surface exudate is produced as the meat surface area increases. This is due to increased cellular disruption resulting from cutting intact muscles and releasing cellular contents. One could take advantage of this principle by fine grinding or chopping the shank meat and adding this material back to batches of product to be massaged or tumbled. Also, reduced particle size further facilitates pumping and stuffing of the mechanically worked meat. However, using pieces smaller than about 1/2 pound may interfere with the desired intact muscle appearance and texture.

External and seam fat on meat pieces has a detrimental effect on bind strength and yield. All trimmable fat should be removed for optimum quality and yield.

Binding strength also depends upon the meat temperature during tumbling or massaging. Salt soluble proteins are extracted over a wide range of temperatures, but are most readily extracted from lean meat at 36 to 38 degrees F (2.2- 3.3 degrees C). This supports the findings that the bind strength of ham was much better when massaged at 30 degrees F and 40 degrees F (-0.9 degrees C and 4.4 degrees C) than at 50 degrees F (10 degrees C). In one of the original U.S. patents dealing with mechanical conditioning of meat, the mechanical action was observed to be enhanced by chilling the pieces of cured meat to as low as 25 degrees F, (-3 degrees C) then mixing the product until it reached a temperature of about 35 degrees F (1.7 degrees C). This phenomenon could be approached by using refrigerated tumblers, massagers, etc. or by direct addition of CO2 to such equipment. Meat with greater fatty tissue should be massaged at higher temperatures to make the fat and connective tissue more pliable and more easily disrupted, respectively.

Vacuum tumbling or mixing, improves bind strength by reducing protein foaming. Foaming denatures proteins and subsequently, decreases bind strength. Vacuum has been credited with increasing the amount of protein extracted and decreasing the time required to produce the optimal product. Normally, the massaging treatment is not rigorous enough to require vacuum.

Fresh hams should be boned prior to brine injection as consistent pump levels are more difficult to achieve due to presence of and/or weight of bone. A boneless ham is easier to stitch pump and the resultant fresh trimmings are worth more than cured trimmings. This author recommends that if a processor sees the need for curing prior to boning, that the cured, bone-in items not be sorted under an immersion cure prior to boning and tumbling or massaging.

The curing pickle should be injected at about 45 degrees F. It might be wise to set target injection levels slightly below the desired level as pickle can easily be added later to the tumblers or massagers. Additional pickle added to tumblers or massagers will be readily absorbed by the meat. The pickle should at least include sufficient ingredients to produce a final product containing 2 to 2.5 percent salt (NaCl) and 0.3 percent alkaline phosphates. A mixture of sodium tripoly and hexametaphosphates is normally used.

It is not recommended that processors inject hams to 30 or 40 percent of green weight in order to achieve the maximum allowable added moisture in S/F products. Pumping over 25 percent of green weight increases cook loss and decreases bind strength.

Hams which have been frozen and thawed once do not seem to result in an inferior binding product as compared to non-frozen hams; however, this will depend on the methods used for freezing and thawing. When using thawed meats, be sure to collect and weigh thaw drip as part of the ingoing green weight and add to the tumbler or massager. This deep red juice, often considered to be blood, is cell sap and is high in protein.

Following the stitch pumping of boneless whole hams, one may want to separate or chunk hams into smaller pieces. Smaller pieces, as mentioned previously, facilitate extraction of protein exudate and the subsequent stuffing process through moist stuffing machines. Also, whole hams could be separated at this stage at natural muscle seams to allow for separation of individual muscles. Color, pH, and waterholding capacity have been reported to vary more between different muscles of the same hams than between muscles of different hams. By combining muscles of the same type in one product two-toning is prevented and the uniformity of the product quality is enhanced.

Following maceration, the pumped hams plus any additional pickle (to correct pump level) are added to tumblers or massagers. Since massaging units usually involve square vats, it is essential to check that all meat pieces are being moved about the vat and receiving equal physical treatment. This author also suggests that massagers (which are normally open to the dehydrating effects of refrigeration units) be covered to get even better yields.

Finally, if massagers of non-vacuum tumblers are used, a quick run through a vacuum mixer or stuffer would help to remove unwanted air from the product. Product should be stuffed within 30 minutes after being removed from tumblers or massagers to prevent difficulty in stuffing and poor finished product appearance.