Food Biochemistry and Food Processing (2 edition)

BLBS102-c18 BLBS102-Simpson March 21, 2012 13:30 Trim: 276mm X 219mm Printer Name: Yet to Come

336 Part 3: Meat, Poultry and Seafoods

Figure 18.4.Sausage stuffed into a collagen casing, 80-mm

diameter, and clipped on both extremes.

although the operation takes only a short time, just a few min-

utes, and the ratio of bowl speed to knife speed determines the

desired particle size.

PROCESSING STAGE 2: STUFFING

The mixture is stuffed under vacuum into casings—natural,

collagen-based, or synthetic—with both extremes clipped. The

vacuum avoids the presence of bubbles within the sausage and

disruptions in the casing. The stuffing must be adequate in or-

der to avoid smearing of the batter, and temperature must be

kept below 2◦C to avoid this problem. Once stuffed (Fig. 18.4),

the sausages are hung in racks and placed in natural or air-

conditioned drying chambers.

PROCESSING STAGE 3: FERMENTATION

Fermentation Technology

Once sausages are stuffed, they are placed in computer-

controlled air-conditioned chambers and left to ferment for mi-

crobial growth and development. A typical chamber is shown in

Figure 18.5. Temperature, relative humidity, and air speed must

be carefully controlled in order to have correct microbial growth

and enzyme action. The whole process can be considered as a

lactic acid solid-state fermentation in which several simultane-

ous processes take place: (1) microbial growth and development,

(2) biochemical changes, mainly enzymatic breakdown of carbo-

hydrates, proteins, and lipids, and (3) physical changes, mainly

acid gelation of meat proteins and drying.

Meat fermentation technology differs between the United

States and Europe. High fermentation temperatures (35–40◦C)

are typical in US sausages, followed by a mild heating process, as

a kind of pasteurization, instead of drying, to kill anyTrichinella.

Thus, starters such asLactobacillus plantarumorPediococcus

Figure 18.5.Example of a fermentation/drying chamber with

computer control of temperature, relative humidity, and air rate. (By

courtesy of Embutidos y Conservas Tabanera, Segovia, Spain.)

acidilactici,which grow well at those temperatures, are typically

used. In Europe, different technologies may be found, depending

on the location and climate. There is a historical trend toward

short-processed, smoked sausages in cold and humid countries,

as in Northern Europe, and long-processed, dried sausages in

warmer and drier countries, as in the Mediterranean area. In the

case of Northern European countries, sausages are fermented

for about 3 days at intermediate temperatures (25–30◦C), fol-

lowed by short ripening periods (up to 3 weeks). These sausages

are subjected to a rapid pH drop and are usually smoked for

a specific flavor (Demeyer and Stahnke 2002). On the other

hand, Mediterranean sausages require longer processing times.

Fermentation takes place at milder temperatures (18–24◦C) for

about 4 days, followed by mild drying conditions for a longer

time, usually several weeks or months.L. sakeiorL. curvatusare

the lactic acid bacteria most often used as starter cultures (Toldr ́a

et al. 2001). The time required for the fermentation stage is a

function of the temperature and the type of microorganisms used

as starters.

The technology is quite different in China and other Asian

countries. Sausages are first dried over charcoal at 48◦C and

65% relative humidity for 36 hours and then at 20◦C and 75%

relative humidity for 3 days. Water activity rapidly drops below

0.80, although pH remains at about 5.9, which is a relatively high

value. Fermentation is relatively poor, and the sour taste, which

is considered undesirable, is reduced. Chinese raw sausage is

consumed after heating (Leistner 1992).

Microbial Metabolism of Carbohydrates

The added carbohydrate is converted, during the fermentation,

into lactic acid of either thed(−)orl(+) configuration, or a mix-

ture of both, depending on the species of lactic acid bacteria used