1. Foodborne Illness and Sous Vide Cooking
Sous vide cooking,
when done properly, can safely create amazingly tender chicken, a perfect soft-cooked egg,
or a succulent steak. However, it’s also possible to set up a perfect breeding ground for
bacteria if the food is mishandled. The heat involved in sous vide cooking is very low, so
if you start with, say, a very large piece of frozen meat, it will take a long time to
come up to temperature and will spend too much time in the breeding ranges of common
foodborne pathogens.
With sous vide cooking, it is possible to cook meats to a point where they are
texturally done—proteins denatured—but have not had sufficient time at heat for bacteria
and parasites to be rendered nonviable. For these reasons, sous vide cooking has run afoul
of some restaurant health inspectors: without proper procedures and clear guidelines,
pathogens such as listeria and botulism are valid concerns when the food is mishandled.
These concerns can be addressed with a clear understanding of where the risks are and what
factors mitigate them. With the popularity of sous vide cooking on the rise, health
inspectors are creating new guidelines, and depending upon where you live, they might
already be comfortable blessing restaurants that have demonstrated proper handling
procedures.
With low-temperature cooking, it’s possible to violate the “40–140°F / 4–60°C danger
zone” rule and its derivative rule:
Thou shalt pasteurize all potentially contaminated
foods.
In the FDA’s Bad Bug Book, the highest survival temperature
listed for a foodborne pathogen at the time of this writing is 131°F / 55°C, for
Bacillus cereus, which is relatively uncommon (you’re 50 times more
likely to get ill from salmonella) and, while unpleasant, has caused no known fatalities.
The next highest survival temperature listed by the FDA is 122°F / 50°C, which gives you
an idea of how much of an outlier B. cereus is.
Why is the danger zone a problem for dishes cooked sous vide, even at temperatures
high enough to kill bacteria? The issue is that food cooked sous vide takes longer to come
up to temperature than food cooked via other methods, and during that time heat-stable
toxins can form. A number of foodborne illnesses are brought about by toxins and spores
produced by bacteria. Even if the bacteria are killed, there could be sufficient time for
them to produce enough toxins to be harmful in overly large cuts of meat. To be
safe, make sure that the core temperature of your food product reaches temperature
within two hours.
The temperatures in the danger zone rule build in a safety cushion, and for a broad,
simple rule for all consumers, this is a good thing. If you are going to violate the
temperature rules—e.g., cooking fish to only a rare temperature—be aware that you risk
contracting a foodborne illness. For sous vide dishes that go from fridge to plate in less
than two hours and where the danger zone rule is violated, the risks
are equivalent to eating the raw item. If you are comfortable eating beef tartar or raw
tuna in sushi, foods cooked sous vide are no worse when properly handled. Still, if you
are cooking for someone who is in an “at-risk” group, you should avoid serving these foods
just as you would avoid serving raw or undercooked items, especially as you can prepare a
number of dishes sous vide that pasteurize the food and taste fantastic.
Sous vide cooking methods can be grouped into two general categories: cook-hold and
cook-chill. In cook-hold, the food is heated up and held at that
temperature until it is served. In cook-chill, the food is heated up,
cooked, then rapidly chilled in the fridge or freezer for later use.
(Use an ice-water bath to shock the food.) With the cook-chill approach, a greater amount
of cumulative time is spent in the danger zone: first while the food is being heated, then
while it’s being chilled, and then while it’s being heated again. Since it’s the
cumulative time in the danger zone that is of concern, I find it easier to use the
cook-hold method, so that I simply don’t have to worry about the cumulative time.
For the home chef concerned about food safety (that is all of
you, right?), there is an easy way to remain safe (well, safer; it’s
all about risk mitigation and relative risks). When cooking sous vide, give preference to
the cook-hold method, and be aware of the minimum temperatures required for
pasteurization. This is an oversimplification, but it’s an easy rule to follow. The better
boundary guideline is to make sure to get the food above 136°F / 58°C—the lowest
temperature given in the FSIS food guidelines—within a two-hour window and to hold it
above that temperature for long enough to pasteurize it.
Note:
You can hold food above 140°F / 60°C for as long as you want; it’s actually
safer than storing food in the fridge.
Pasteurization is not an instantaneous process. For food to be
pasteurized, it must be held at the target temperature for a
sufficient length of time for the appropriate reduction of bacteria to occur. Consumer
guidelines for cooking meats such as poultry specify temperatures of 165°F / 74°C because
at that temperature the bacterial count will be reduced so quickly that there is no need
to address the concept of hold time, and slight errors in temperature measurement and
thermometer calibration will not be of concern.
With meats such as chicken breast, the required hold time at 140°F / 60°C for enough
bacteria to die can be half an hour or more, meaning the food needs to reach 140°F / 60°C
and then sit at that temperature for at least the prescribed amount of time.
Invariably, some people raise their eyebrows when I
first start to describe sous vide cooking. The idea of cooking in a water bath is just
plain foreign at first. But remember: cooking is about the application of heat,
regardless of the source of that heat. Sous vide cooking is not the same as boiling food
(that’d require the water to be around 212°F / 100°C). It’s not even like simmering or
poaching, in which the liquid environment is often hotter than the target temperature.
Sous vide is the application of a very low, controlled temperature, in some cases as low
as 116°F / 47°C.
Consider a piece of salmon cooked to medium doneness, which is an internal
temperature of around 126°F / 52°C. On the grill, you’d cook the salmon until the core
temperature reached 126°F / 52°C, but by that point, the outer portions of the fish
would be hotter. In a water bath at 126°F / 52°C, the entire piece of fish would reach
that temperature—but no higher. A ¾″ / 20 mm-thick fillet of salmon will cook to medium
in about 30 minutes at 126°F / 52°C.
Note:
Note that this temperature does not pasteurize the salmon.
Handle it like raw/undercooked fish.
If you’re anything like me, at some point, the following thought will occur:
wait a second, my tap water is about that hot...hmm... I’ve tried
it, and it does work: place your fish (sealed in an airtight bag)
in a container in your sink, flip open the hot water tap, and keep a slow, constant
trickle running. Check the temperature with a thermometer, and set your timer. It’s not
exactly energy efficient, even at a slow trickle, but it does work,
sorta, at least for fish. Foods like chicken and beef require water hotter than what
your tap delivers, and even if you did manage to get a stream of 140°F / 60°C water out
of your tap, long cook times (e.g., 24-hour brisket) would make it impractical.
So, the next thought a geek might have would be: wait a sec, did you say
140°F / 60°C? That’s about how hot dishwashers get! Search online for
“dishwasher recipes” and yup, it has been done. People have cooked fish and even
vegetarian lasagna in their dishwashers. If you try it, just remember to keep the time
from fridge to plate at two hours or less, and treat the food as potentially raw or
undercooked.
