Modernist-Cuisine-Vol.-1-Small

3
T H E HA Z ARDS OF
Punctured Meat
Although contamination of intact muscle meat is almost
always limited to the surface, it’s important to recognize that
poking, perforating, or otherwise puncturing whole pieces
of meat can introduce pathogens into their interior. Sticking
a temperature probe into the center of a piece of meat can
contaminate it; injecting brines or marinades can, too.
Gunshots also penetrate flesh, carrying any pathogens on an
animal’s skin or feathers into the muscle interior, so wild
game should be considered to be at high risk of internal
contamination and cooked accordingly.
Mechanical meat tenderizers such as the Jaccard, which
are used increasingly in the commercial processing of beef,
also carry contamination to the interior. Mechanically tenderized
beef has been blamed for at least four outbreaks of
foodborne illness in the past decade alone. In December
2009, for example, tenderized or “needled” steaks and sirloin
tips from a processing company in Oklahoma caused Escherichia
coli-associated illness in 16 states, moving the USDA to
consider special labeling requirements for needled beef.
Cooks, beware: Jaccarding a steak (as described on page
3·50) poses the same risks because a Jaccard tenderizer
perforates meat. The same is true for meat sold pretenderized,
which is much more common than you might think.
During tenderization, the tines carry pathogens into the
meat, where they are less likely to be killed by heat if the
meat is served rare.
If you are really concerned about the contamination of
punctured meat, then you can dip the meat in a hot blanching
bath for a short time or pass a torch over the meat’s
surface before tenderizing it with a Jaccard or other penetrating
meat tenderizer. For more detail on blanching and
searing strategies, see page 2·267.
In the Zone
Food safety rules typically specify a “danger zone” of temperatures from
4.4–60 °C / 40–140 °F at which food cannot be left out for more than four
hours. But as these graphs show, all temperatures within the danger zone
are not equally dangerous. The top graph shows the wildly different rates at
Growth rate
High
Low
Temperature (˚F)
40 50 60 70 80 90 100 110 120
10 20 30 40 50
Temperature (˚C)
Fastest growth occurs
at 41.5 ˚C / 107 ˚F
which Salmonella bacteria grow at various temperatures within the danger
zone. The lower graph gives a different perspective on this phenomenon
by showing how long at each temperature the bacteria require to multiply
as much as they do in four hours at 41.5 °C / 107 °F.
On chicken meat, Salmonella reproduce fastest at 41.5 °C / 107 °F.
Notice, however, how much the growth rate drops at lower
temperatures and plummets even more sharply at temperatures
above the peak.
Although it doesn’t make sense to
specify maximum and minimum
temperatures for the “danger zone,”
it is perfectly reasonable to do so
for holding temperatures, such as
the maximum permissible temperature
for a refrigerator.
two hours; USDA fact sheets say the limit is just
one hour if the ambient temperature is more than
32 °C / 90 °F.
If you peruse the FDA 2009 Food Code, however,
the “danger zone” turns out to be a much
more complicated topic than simple fact sheets
suggest. The general temperature range for foods
is 5–57 °C / 41–135 °F, but there are several
exceptions. Eggs, for some reason, are allowed to
be stored at 7 °C / 45 °F. Food that is cooked at
54 °C / 130 °F can be held at that temperature.
The time duration is also complicated. Food
that starts off cold (i.e., 5 °C / 41 °F or below) can
spend four hours at 5–57 °C / 41–135 °F. Or you
can apply an alternative standard that it can spend
six hours at 5–21 °C / 41–70 °F. And many exceptions
are given.
If you are cooling hot food, then it must spend
no more than two hours in the range 21–57 °C /
70–135 °F and no more than six hours in total at
5–57 °C / 41–135 °F. Of course there are exceptions
here, too, because the FDA allows some
foods to be cooked at no more than 54 °C / 130 °F.
Many people try to avoid this complexity by
simplifying the standard to “four hours in the
danger zone.” This can be a useful simplification,
but we should all understand that it is just that
a gross simplification of the underlying dynamics
of microbial growth.
On chicken meat, for example, Salmonella
begins growing slowly at temperatures above 4 °C
/ 39 °F, reaches its peak growth rate at 41.5 °C /
107 °F, then declines sharply until it stops growing
and begins to die at 49 °C /120 °F (see top graph
on next page). Temperatures at which peak growth
occurs are clearly the most dangerous. The
“danger zone” limit of four hours is designed to
ensure that, even at those temperatures, Salmonella
bacteria would not grow in sufficient numbers
to cause illness.
Some simple calculations reveal the varied risk
within a broader temperature range. If four hours
within the “danger zone” is taken as the upper
safety limit, that means that, even at 41.5 °C /
107 °F, the temperature at which peak Salmonella
growth occurs, four hours’ worth of growth is still
safe. We can plot the time required for the same
amount of bacterial growth at other temperatures.
The surprising result, as the bottom graph on the
next page shows, is that four hours at the peak
temperature produces the same amount of bacterial
growth as 1.3 years at 4 °C / 39 °F!
Time
1y
12 wk
4wk
7 d
24 h
12 h
6h
40 50 60 70 80 90 100 110 120
1.3 years at 4.0 ˚C / 39.0 ˚F
5 days at 10 ˚C / 50 ˚F
18 hours at 20 ˚C / 68 ˚F
Temperature (˚F)
5 weeks at 48 ˚C / 118.4 ˚F
7 hours at 30 ˚C / 86 ˚F 4 hours at 41.5 ˚C / 107 ˚F
10 20 30 40 50
Temperature (˚C)
To offer another way to think about the differing risks posed by different temperatures, we
calculated how long at each temperature Salmonella would need on chicken to achieve the
same multiplication in number of bacteria that occurs in four hours at 41.5 °C / 107 °F. The
bacteria could sit at 4 °C / 39 °F for more than year, or at 48 °C / 118 °F for five weeks.
Salmonella bacteria begin to die at temperatures above 48 °C / 118 °F. At temperatures
below 4 °C / 39 °F, the bacteria stop growing but do not die, even when frozen.
176 VOLUME 1 · HISTORY AND FUNDAMENTALS
FOOD SAFETY 177