125Chapter 6
Curing
Karl O. Honikel
Introduction
In its original meaning, curing means cor-
recting, making better, that is, treating sick
people, curing disease, or in our subject, pre-
serving, drying, salting, pickling, or smoking
a piece of meat ( The New Penguin Thesaurus
2000 ). Curing is supposed to enhance the
shelf life of meat by preserving and avoiding
spoilage with the help of salt, acid (pickle),
or drying and/or smoking. In a narrower
sense today (and this is the meaning used in
this chapter), we understand meat curing to
be the addition of salt with or without nitrite
and/or nitrate during the manufacture of meat
products.
Originally, meat curing was the addition
of rock salt, sea salt, or mined salt to an
unheated piece or small cuts of meat in order
to lower the water activity, prevent microbial
growth and chemical spoilage, tenderize the
meat, and add fl avor to the product.
In the 19th century, meat processors real-
ized that some salts preserved better than
others and also some were better at enhanc-
ing and stabilizing the product ’ s red color.
Saltpeter (KNO 3 ) was recognized as the con-
taminant of these “ better ” salts. The chemical
reactions behind it, however, remained
unknown. Known for centuries for its oxida-
tive power in gunpowder (carbon + KNO 3 ),
saltpeter was known as an oxidative
compound.
Thus the reaction of nitrate in preserving
or in preventing oxidative changes (rancid-
ity) remained a secret until Polenske (1891)
from the German Imperial Health Offi ce
published experiments where he could
prove that by adding nitrate (saltpeter) to a
pickling solution, nitrite was formed, appar-
ently due to the action of microorganisms
in the brine. Lehmann (1899) and Kisskalt
(1899) confi rmed that nitrite was the agent
producing meat ’ s red color and heat stability.
Haldane (1901) shed light on the chemistry
of the curing process by showing that redox
reactions occurred in meat on curing. He
also extracted the NO - myoglobin as the sub-
stance responsible for the bright red color of
cured meat. Hoagland (1910, 1914) showed
that the nitrite anion was not the reactant;
it was the nitrous acid (HNO 2 ) or a metabo-
lite of it, such as NO, that reacted with the
myoglobin, as shown in the equations in
Figure 6.1.
The coloring of meat by nitrogen com-
pounds was understood at the turn of the 20th
century, but the antimicrobial and fl avoring
action was still thought to be mainly due to
the salt (NaCl) concentration. Only in the last
two decades was light shed on the action of
nitrite on fl avor and preservation (Grever and
Ruiter 2001 ; EFSA 2003 ; L ü cke 2008 ).
Nitrite or nitrous acid formed as shown by
the fi rst equation in Figure 6.1 , when reduced
by microbial action is able to sequester
oxygen in a meat batter, chemically reacting
in the reverse direction to form nitrate, thus
preventing oxidative (rancidity) processes.
(Honikel 2008 ; Fig. 6.2 ). Also, the formation
of fl avoring substances, mainly from fatty
acids, during storage and preparation of meat