Text 9. Methods of Smoking

Several methods are used to apply smoke. The traditional and most widely used method is in a smokehouse. The product is hung from racks or trees which, in turn, are placed in the sealed house. Smoke is gen­erated outside of the house by the controlled combustion of moist sawdust, or by the friction of a rapidly moving steel plate against the end of a log or board. Smoke is carried into the house by a system of fans. Because of their low resin content, hardwoods, usually oak or hickory, are most commonly used to generate the smoke. Softwoods are also used in order to achieve special flavor effects.

The modern smokehouse is equipped to heat processed meat products as well as to apply smoke. In order to accomplish both processes, the temperature, density of the smoke, and the relative humidity are care­fully controlled. In many cases, smoke is applied during the initial phase of cooking, or even before cooking the product. The smoke density determines the length of time that products must be smoked in order to achieve the desired level of smoke deposition. This is a very important factor in modern continuous process frankfurter production, where the franks must be exposed to large volumes of smoke in a short period of time. Continuous smokehouses are now in use that are capable of smok­ing and heat processing frankfurters in 30-60 minutes.

Humidity control in the smokehouse is important for several reasons, the most important of which is to insure a high yield of cooked product. At the start of a cooking schedule, relative humidity can be high, but as the temperature increases, it will decrease, and a significant loss in product weight, as moisture, can occur. Acceptable weight losses range from 5-10 percent, depending somewhat upon the particular product. In addition to decreasing shrinkage, a high relative humidity during cooking makes the casings more permeable to smoke, speeds cooking, and eases casing removal after chilling. However, excessively high rel­ative humidity can contribute to emulsion breakdown, and to the ap­pearance of surface grease.

Electrostatic smoking processes have been developed in an attempt to speed smoke deposition, but these processes have not achieved widespread commercial application. Liquid smoke preparations have been developed as an attempt to eliminate the smoking process. Liquid smoke is prepared by the condensation and fractional distillation of wood smoke. It is usually applied as an aqueous spray on the product surface. Liquid smoke preparations are free of carcinogenic compounds, such as benzopyrene, that have been discovered in low levels in natural wood smoke. The presence and amount of carcinogens in natural smoke depends somewhat upon the temperature at which the smoke is generated. The danger of carcinogenesis from natural smoke in meat products seems negligible. However, if it becomes necessary to elim­inate the use of natural smoke, the use of liquid smokes will probably increase. These preparations are widely used in Europe at present.

Text 10. Aging

In many meat products with a reduced moisture content, drying occurs simultaneously with the next processing step – aging. This process involves keeping the manufactured product for varying periods under controlled temperature and humidity conditions. There are several purposes for aging processed meat, including: (1) flavor development, (2) textural changes, (3) completion of the various curing reactions, and (4) the drying and hardening of the product. The develop­ment of a distinctive flavor often results from microbial fermentation in the product. The organisms responsible for fermentation are usually lactic acid producing bacteria that can enter the product from the plant environment and processing equipment. To achieve uniform quality in various fermented products, many processors now add specific lactic acid producing microorganisms as a starter culture.

The aging period is also necessary for proper cure development. This is especially true when the curing mixture contains only nitrate, since time must be allowed for the growth of nitrate reducing bacteria, and for the conversion of nitrate to nitrite. Some lactic acid producing bacteria do not reduce nitrate, so when they are used as starter cultures to ac­celerate fermentation, nitrite must also be included in the cure. Two types of textural changes may occur. Tenderization may occur due to the action of autolytic enzymes that are present in muscle. More commonly, the product will become firmer or harder due to a loss of moisture during drying. Varying amounts of moisture loss are desired, depending upon the product. However, in all cases the rate of drying is closely controlled. Too rapid a drying rate, especially ini­tially, will result in loss of moisture primarily from the surface, and the development of a hard exterior that will retard or prevent the proper drying of the interior. If the drying rate is too slow, the surface will be moist enough to support excessive mold, bacterial, or yeast growth.

Aging can either follow or precede the smoking process, depending upon the particular product. Quite often, aged products are not fully heat processed, but are only subjected to a cold smoke. For example, semidry fermented sausages are heat processed at a minimum tempera­ture of 56.5°C, whereas dry sausages, such as summer sausage and salami, never exceed a temperature of 32°C during their manufacture. In addition to semidry and dry fermented sausages, country cured hams are an example of an aged processed meat product. The length of the aging period for these products varies from 1 week to several months, de­pending largely upon the amount of moisture loss that is desired. Country cured hams are aged for 3-6 months, during which time they will shrink at least 18 percent due to moisture loss. Salami is aged for an average of 90 days, and will sustain an average moisture loss of 25 percent during this time.

Text 11. Casings

Casings are widely used as forms and containers for sausages. The process of placing meat products, either comminuted or noncommi­nuted, into casings is referred to as stuffing. Two types of casings are in general use: (1) natural, and (2) manufactured.

Prior to the development of manufactured cas­ings, only natural casings were available to meat processors. They are derived almost exclusively from the gastro-intestinal tracts of swine, cattle, and sheep. Hog casings are prepared from the stomach, small intestine (smalls), large intestine (middles), and terminal end (colon) of the large intestine (bungs). The parts of cattle used for beef casings are the esophagus (weasands), small intestine (rounds), large intestine (middles), bung, and bladder. Only the intestines of sheep are used to produce sheep casings.

Natural casings are very permeable to moisture and smoke. One of their most important characteristics is that they shrink and thereby re­main in close contact with the surface of a sausage as it loses moisture. Thus, they are often used in dry sausage manufacture. Most natural casings are digestible and can be eaten.

Manufactured casings. Four classes of manufactured casings are available: (1) cellulose, (2) inedible collagen, (3) edible collagen, and (4) plastic. Cellulose casings are prepared from cotton linters (the short fibers that are closest to the seed). These are first dissolved and then regenerated into casings. Other sources of cellulose have been success­fully used. Cellulose casings are manufactured in sizes ranging from 1.5 centimeters in diameter, for small sausages, up to 15 centimeters for large sausages such as bologna. They are manufactured with stretch and shrink characteristics similar to those of natural casings. The inner surface of the casing is sometimes coated with an edible, water soluble dye that transfers to the sausage surface and artificially colors the product. The advantages of cellulose casings include their ease of use, the variety of sizes that are available, and their uniformity of size, greater strength, and low microbial levels. Their strength is especially important in view of the widespread use of automated processing procedures. Fibrous cellulose casings, consisting of cellulose extruded on a paper base material, are very strong and are used for large sausages (bologna) and roll-type items (turkey rolls).

Both edible and inedible collagen casings are regenerated from col­lagen extracted from skins and hides. The inedible collagen casings combine some of the advantages of both cellulose and natural casings; especially their strength, uniformity, and shrink characteristics. They must be removed prior to consumption of the products, as must cellulose casings. Edible collagen casings are used largely for fresh pork sausage and frankfurters. They are very uniform in physical characteristics and have greater strength than natural casings.

Plastic tubes or bags are used as sausage containers in certain appli­cations. They are impermeable to smoke and moisture. Therefore, they are used with products which are not smoked, such as fresh pork sausage or liver sausage, or with products which are heat processed in hot water.

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