108 Modern Food Microbiology
BACON AND CURED HAMS
The nature of these products and the procedures employed in preparing certain ones, such as smoking
and brining, make them relatively insusceptible to spoilage by most bacteria. The most common form
of bacon spoilage is moldiness, which may be due to Aspergillus, Alternaria, Fusarium, Mucor,
Rhizopus, Botrytis, Penicillium, and other molds (Table 5–1). The high fat content and low a w make
it somewhat ideal for this type of spoilage. Bacteria of the genera Enterococcus, Lactobacillus, and
Micrococcus are capable of growing well on certain types of bacon such as Wiltshire, and E. faecalis
is often present on several types. Vacuum-packaged bacon tends to undergo souring due primarily to
micrococci and lactobacilli. Vacuum-packed, low-salt bacon stored above 20
◦ C may be spoiled by
staphylococci.
92
Cured hams undergo a type of spoilage different from that of fresh or smoked hams. This is due
primarily to the fact that curing solutions pumped into the hams contain sugars that are fermented
by the natural biota of the ham and also by those organisms pumped into the product in the curing
solution, such as lactobacilli. The sugars are fermented to produce conditions referred to as “sours” of
various types, depending on their location within the ham. A large number of genera of bacteria have
been implicated as the cause of ham sours, among which are Acinetobacter, Bacillus, Pseudomonas,
Lactobacillus, Proteus, Micrococcus, and Clostridium. Gassiness is not unknown to occur in cured
hams where members of the genus Clostridium have been found.
In their study of vacuum-packed sliced bacon, Cavett
13 and Tonge et al.
92 found that when highsalt bacon was held at 20
◦ C for 22 days, the catalase-positive cocci dominated the biota, whereas at
30
◦ C the coagulase-negative staphylococci became dominant. In the case of low-salt bacon (5–7%
NaCl versus 8–12% in high-salt bacon) held at 20
◦ C, the micrococci as well as E. faecalis became
dominant; at 30
◦ C the coagulase-negative staphylococci as well as E. faecalis and micrococci became
dominant. In a study of Iberian dry-cured hams, over 97% of the isolates were staphylococci with the
four predominant species being S. equorum, S. xylosus, S. saprophyticus, and S. cohnii.
77 Interestingly,
one S. xylosus isolate hybridized with a DNA probe for staphylococcal enterotoxins C and D, but the
investigators noted that probe-positive isolates do not always produce enterotoxins.
In a study of lean Wiltshire bacon stored aerobically at 5
◦ C for 35 days or 10
◦ C for 21 days,
Gardner
35 found that nitrates were reduced to nitrites when the microbial load reached about 10
9 /g.
The predominant organisms at this stage were micrococci, vibrios, and the yeast genera Candida and
Torulopsis. Upon longer storage, microbial counts reached about 10
10 /g with the disappearance of
nitrites. At this stage, Acinetobacter, Alcaligenes, and Arthrobacter-Corynebacterium spp. became
more important. Micrococci were always found, whereas vibrios were found in all bacons with salt
contents >4%. In a study of Italian dry fermented sausages, the most frequently isolated staphylococci
were S. xylosus followed by S. saprophyticus, S. aureus, and S. sciuri.
34 S. xylosus appears to be the most
frequently isolated from several Italian dry sausages. In Iberian dry cured hams, the two predominant
organisms in the ripening process are Staphylococcus equorum and S. xylosus, and both are believed
to contribute to product flavor.
Safety
Overall, fermented meat products have a long history of safety throughout the world. This is not to
imply that they are never the vehicles of foodborne illness outbreaks, but when such incidents have
occurred they have been sporadic. Several outbreaks of illness occurred in the United States in the
1990s involving fermented meat products as vehicles. As a consequence, the USDA mandated a log 10
BACON AND CURED HAMS
The nature of these products and the procedures employed in preparing certain ones, such as smoking
and brining, make them relatively insusceptible to spoilage by most bacteria. The most common form
of bacon spoilage is moldiness, which may be due to Aspergillus, Alternaria, Fusarium, Mucor,
Rhizopus, Botrytis, Penicillium, and other molds (Table 5–1). The high fat content and low a w make
it somewhat ideal for this type of spoilage. Bacteria of the genera Enterococcus, Lactobacillus, and
Micrococcus are capable of growing well on certain types of bacon such as Wiltshire, and E. faecalis
is often present on several types. Vacuum-packaged bacon tends to undergo souring due primarily to
micrococci and lactobacilli. Vacuum-packed, low-salt bacon stored above 20
◦ C may be spoiled by
staphylococci.
92
Cured hams undergo a type of spoilage different from that of fresh or smoked hams. This is due
primarily to the fact that curing solutions pumped into the hams contain sugars that are fermented
by the natural biota of the ham and also by those organisms pumped into the product in the curing
solution, such as lactobacilli. The sugars are fermented to produce conditions referred to as “sours” of
various types, depending on their location within the ham. A large number of genera of bacteria have
been implicated as the cause of ham sours, among which are Acinetobacter, Bacillus, Pseudomonas,
Lactobacillus, Proteus, Micrococcus, and Clostridium. Gassiness is not unknown to occur in cured
hams where members of the genus Clostridium have been found.
In their study of vacuum-packed sliced bacon, Cavett
13 and Tonge et al.
92 found that when highsalt bacon was held at 20
◦ C for 22 days, the catalase-positive cocci dominated the biota, whereas at
30
◦ C the coagulase-negative staphylococci became dominant. In the case of low-salt bacon (5–7%
NaCl versus 8–12% in high-salt bacon) held at 20
◦ C, the micrococci as well as E. faecalis became
dominant; at 30
◦ C the coagulase-negative staphylococci as well as E. faecalis and micrococci became
dominant. In a study of Iberian dry-cured hams, over 97% of the isolates were staphylococci with the
four predominant species being S. equorum, S. xylosus, S. saprophyticus, and S. cohnii.
77 Interestingly,
one S. xylosus isolate hybridized with a DNA probe for staphylococcal enterotoxins C and D, but the
investigators noted that probe-positive isolates do not always produce enterotoxins.
In a study of lean Wiltshire bacon stored aerobically at 5
◦ C for 35 days or 10
◦ C for 21 days,
Gardner
35 found that nitrates were reduced to nitrites when the microbial load reached about 10
9 /g.
The predominant organisms at this stage were micrococci, vibrios, and the yeast genera Candida and
Torulopsis. Upon longer storage, microbial counts reached about 10
10 /g with the disappearance of
nitrites. At this stage, Acinetobacter, Alcaligenes, and Arthrobacter-Corynebacterium spp. became
more important. Micrococci were always found, whereas vibrios were found in all bacons with salt
contents >4%. In a study of Italian dry fermented sausages, the most frequently isolated staphylococci
were S. xylosus followed by S. saprophyticus, S. aureus, and S. sciuri.
34 S. xylosus appears to be the most
frequently isolated from several Italian dry sausages. In Iberian dry cured hams, the two predominant
organisms in the ripening process are Staphylococcus equorum and S. xylosus, and both are believed
to contribute to product flavor.
Safety
Overall, fermented meat products have a long history of safety throughout the world. This is not to
imply that they are never the vehicles of foodborne illness outbreaks, but when such incidents have
occurred they have been sporadic. Several outbreaks of illness occurred in the United States in the
1990s involving fermented meat products as vehicles. As a consequence, the USDA mandated a log 10