320 Chapter 17
average cutting coverage, calculated on the
basis of chopping time, number of rotations/
minute, knife number, and cutting fl at edge,
usually equals the mean circumference of the
bowl of an industrial chopper (8 min *3000 rpm (^6) 25 μ m = π (^) * 1.15 m = ∼ 3.6 m;
Puolanne 1999 ). Consequently, industrial
experience tells us that a fi nely chopped
sausage batter is ready, theoretically, when,
on average, “ all points of the sausage batter
have been hit once by the knife ’ s fl at edge. ”
The knife velocities of today are faster than
ten years ago, reaching 5,000 – 6,000 rpm
(Feiner 2006 ).
The chopping knives also hit fat cells. The
diameters of the fat cells vary between 2 and
120 μ m (Aberle et al. 2001 ). It has been esti-
mated that when a knife moves through the
batter at a speed of 140 m/s, friction heats the
contact surface in the channel up to 80 ° C for
less than 1 msec. This may result in a tran-
sient melting of fat and, consequently, the
formation of emulsion - like structures in the
batter. This requires some kind of emulsifi ca-
tion capacity in the raw batter; otherwise, the
fat would leak out. When sausage batter is
then cooked, the gel that is formed traps the
fat. If there is too much fat, a weak batter
gel and intense chopping with a high end -
temperature allows for fat to be separated. In
larger, visible fatty tissue particles, the fat is
kept in fat cells, which would suggest that
emulsifi cation is not actually required in all
cases. Microscopic studies have shown that
there are, in addition to emulsifi ed fat, intact
fat cells also in fi nely chopped sausages
(Hansen 1960 ), the relative amount of which
depends on the extent of chopping. In some
particular sausages (e.g., liver sausages), the
ingredients are cooked before preparation
and chopped hot, and the product is actually
a water - in - oil emulsion. These products may
also contain larger meat particles, which
means that the product has multiple internal
structures.
The chopper is also a very effi cient mixer.
Chopping brings salt, phosphate (if used),
they are of the same format: the coarsely
ground products are not sausages, since the
meat has been cured in a tumbler and stuffed
before being cooked in the casing. Between
these two extremes are combination prod-
ucts. One type is batter where the meat has
been chopped into a grain the size of a couple
of millimeters. Another type is produced
when the basic batter has been fi nely chopped,
but then larger meat particles (or other
foodstuffs) have been added into the basic
batter.
The linear speed of bowl cutter knives is
about 140 m/s. The sharp blades (the fl at
cutting edge is about 20 – 30 μ m, i.e., the
cutting breadth is about ten times the sarco-
mere length) cut connective tissue and muscle
fi bers into pieces, but fractioned myofi brils
can be seen through a microscope. The
Figure 17.4. Continuous chopper. (Photograph
courtesy of Pertti Leino.)