108 Chapter 5
“ drip. ” Drip can be referred to by a number
of different terms including “ purge loss, ”
“ press loss, ” and “ thaw loss, ” depending on
the method of measurement and when it is
measured. The protein concentration of drip
is about 140 mg ml^ −^1 (i.e., about 70% of that
of meat itself). The proteins in drip are the
intracellular, soluble proteins of the muscle
cells. The red color is due to the protein myo-
globin, the main pigment of meat. Drip loss
occurs throughout the cold chain and repre-
sents a considerable economic loss to the red
meat industry. The potential for drip loss is
inherent in fresh meat and related to the
development of rigor mortis in the muscle
after slaughter and its effect on pH. It is infl u-
enced by many factors. Some of these,
including breed, diet, and physiological
history, are inherent in the live animal.
Others, such as the rate of chilling, storage
temperatures, freezing, and thawing, occur
during processing.
When meat is frozen quickly, the water,
both that released by the fi brils as the meat
has gone into rigor and that which is still
held, is frozen simultaneously. Consequently,
there is no change in the water ’ s relative
positions or amounts. At slower freezing
rates, however, the water balance is altered,
the extracellular water freezing fi rst. As
freezing, continues, the existing ice crystals
grow at the expense of water from the intrafi -
brillar space. When meat is thawed, the
reverse of freezing process occurs. Water that
has been frozen is released and has to rees-
tablish equilibrium with the muscle proteins
and salts. Obviously, if the muscle proteins
have been denatured, they will reabsorb less
water. Since the fi bers have been squeezed
and distorted by ice formation, this nonreab-
sorbed water will lie in wider channels within
the meat structure, thus increasing the poten-
tial drip. If cell walls have also been damaged
by freezing, even less water will be reab-
sorbed and will exude as drip.
Drip potential clearly appears to be related
to species. In general, beef tends to lose pro-frozen storage than carcasses chilled for 1 to
3 days prior to freezing (Harrison et al. 1956 ).
Aging for periods greater than 7 days was
found by Zeigler et al. (1950) to produce
meat with high peroxide and free fatty acid
values when stored at − 18 ° C or − 29 ° C.
Although shorter aging times appear to have
a benefi cial effect on storage life, there is
obviously a necessity for it to be coupled
with accelerated conditioning to prevent any
toughening effects.
There is some evidence that freezing rate
affects the rate of tenderizing after thawing
but not the ultimate tenderness (Dransfi eld
1986 ). Freezing at − 10 ° C more than doubles
the rate, while freezing in liquid nitrogen
almost trebles the rate. Freezing is known to
cause structural damage by ice crystal forma-
tion. It seems likely that ice crystals, particu-
larly small intracellular ice crystals formed
by very fast freezing rates, enhance the rate
of aging by release of enzymes (Dransfi eld
1986 ). Repeated freeze - thaw cycles using
relatively low freezing rates do not seem to
cause any enhanced tenderising (Locker and
Daines 1973 ). There is little evidence of any
relationship between chilling rates and sub-
sequent frozen storage life.
Whether aged or unaged, chilled or frozen,
it is in the cooked fi nal product that the con-
sumer will assess tenderness and texture.
Thus, the way the meat is cooked must
always be considered. The consumers ’ envi-
ronment or setting can also infl uence their
appreciation of tenderness. In one study, con-
sumers were found to be more critical of the
tenderness of beef steaks cooked in the home
than those cooked in restaurants (Miller et al.
1995 ). The Warner - Bratzler force transition
level for acceptable steak tenderness was
between 4.6 and 5.0 kg in the home and
between 4.3 and 5.2 kg in restaurants.
Drip Production
When meat is frozen, its water - hold capacity
is reduced. This in turn gives rise to increased