Further processing of meat

PRINCIPLES OF HEAT TREATMENT FOR NON-STERILIZED PRODUCTS

During processing many meat products are subject to specific heat treatment. The first task of heat treatment is to reach satisfactory shelf-life by reduction of micro-organisms. The second task is to obtain desirable organoleptic characteristics, to preserve nutritive value and improve digestibility of the product.

Reduction of micro-organisms

Bacteria are destroyed if exposed to sufficiently high temperatures for long enough. There is a direct relationship between bacteria survival and time of exposure to temperatures. As an example, if 10 000 000 bacteria (per ml) suspended in broth are exposed to heat (70°C), after the first five minutes 1 000 000 will survive (90 percent are destroyed), after the next five minutes the number of surviving will be 100 000 (again 90 percent are destroyed), and so forth.

This tenfold reduction in bacterial numbers between fixed time intervals is called decimal reduction. The time interval for decimal reduction varies between different bacteria and depends on the temperature applied. The number of bacteria present in a meat product just before the heat treatment (initial number) should be as low as possible so that a shorter time or lower temperature is needed to achieve a satisfactory shelf-life for the product.

As sausage fillings as well as most other meat products represent a very good medium for bacterial growth, they should immediately be exposed to heat treatment in order to prevent bacterial growth. It is also important to perform all operations as quickly as possible, and to maintain the highest hygienic standards so that the initial bacterial count remains as low as possible. The manufacturer must always bear in mind that bacteria grow very fast. Their number may be doubled every 20 minutes.

Organoleptic changes

These are caused by heat treatment (doneness, flavour, firmness, consistency and cured-meat colour development) are time-temperaturedependent processes. The basic effect of the heat treatment is coagulation of meat proteins. Between 70° and 80°C the majority of meat proteins are completely coagulated, forming a structural matrix which entraps fat and water droplets released during heat treatment. With coagulation of meat proteins, WHC is decreased and the meat loses a certain amount of water (thermal weight loss). Those structural changes of proteins are responsible for characteristic firmness of heat-treated products. Frankfurters have an elastic firmness, and on reheating prior to consumption become even more firm. Products containing connective tissue become more tender owing to solubilization of the collagen (gelling). Products such as paste which are in a liquid state prior to heating change for more viscous and spreadable consistency. Sausages made from larger meat pieces also attain a characteristic consistency. The exudate released during massaging or tumbling coagulates and binds the pieces of meat.

144. Temperature measurement in a cooking vat	146. Simple cooking equipment with the movable vat
	145. Temperature measurement with thermometer in large-diameter cooked sausage (centre), during chilling by cold water (showering)

TABLE 8
Influence of temperature and time of heat treatment on cured-meat colour development in bologna (diameter 90 mm)

Such products (cooked hams, ham sausages) become sliceable. Heat treatment also makes products chewable.

In addition to these physical changes resulting from heat treatment, some biochemical reactions also take place which contribute to the typical flavour of heat-treated products. Many compounds present in the raw material are broken down by heat to produce the characteristic flavour. Fatty components give the meat product a distinctive flavour, specific to the animal species from which fat is obtained.

Cured-meat colour is not stable unless the raw product is heat-treated.

All these changes occurring during heat treatment give the product its typical overall sensation of doneness.

Duration of heat treatment

The duration of the heat treatment primarily depends upon the size and shape of the meat product. Treatment continues until the coldest point (innermost part) reaches the defined temperature. It is essential to check temperatures of the heating medium and of the innermost part of the products and to observe exact times (Figs 144 and 145).

TABLE 9
Heat treatment of different meat products

Types of heat treatment

Heat treatment by dry heat is performed in special ovens (roasting) or on a gridiron (grilling). Meat loaves and similar products are roasted. Meat patties, hamburgers and fresh sausages are grilled.

Heat treatment by hotwater is the most common and is usually performed in large cooking vats. When applied to canned hams or ham sausages, it is called pasteurization (Figs 144, 145 and 146).

Heat treatment by steam is one in special steam cabinets and is in particular applied in cases when treatment in cooking vats is not desirable because of substantial losses of aroma and flavour of the products into the cooking water.

Frequent faults committed during heat treatment

Undercooking may be due to the temperature being too low, the time of treatment being too short, or both. The consequences are in a reduced shelflife due to spoilage and the possibility of food-poisoning. Spoilage results in a bad smell, discoloration, softened consistency and souring.

Overcooking results from either too high a temperature or too long a duration or both. The consequences are increased cooking losses, fat separation in some sausages, undesirable changes of flavour and a softer consistency.

General remarks

In order to keep the initial bacterial numbers as low as possible it is important to keep the temperature of the raw materials as low as possible before heat treatment. After filling sausages and mixing other meat products heat treatment must be applied immediately.