Modernist-Cuisine-Vol.-1-Small

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Temperature spiking and internal
variation are both big problems for
storing sous vide foods. For more
on this topic, see page 2·252.
For more on blast chillers and other freezers,
see The Many Ways to Freeze, page 306.
For more on thermometer types and accuracies,
see Measuring Temperature, page 269.
T H E HY G IEN E OF
Bug-Free Ice Cream
warm. Just cover the food to avoid contamination
and don’t leave it out for more than four hours.
The four-hour rule is a bit of a coarse metric,
however, as we’ve already discussed. It is a lot safer
to cool foods quickly. Use an ice bath or crushed
ice in a sous vide bag. Even a dunking in cold tap
water can be tremendously helpful.
Sous vide cook-chilldescribed in chapter 9,
page 2·192 is a great way to store critical food,
because the food stays hermetically sealed after
you pasteurize it. It is the best way, for example, to
handle ice cream base, which otherwise is a classic
contamination hazard (see Bug-Free Ice Cream
below). Sous vide bags also lie flat and cool quickly.
If you’re cooling lots of sauce or stock, pour it
into a shallow container to increase the surface
area. Generally speaking, a shallower pan equals
a faster cooling time. If you cut the depth of the
liquid by half, for example, you’ve cut the cooling
time by a factor of four. You can also divide the
sauce or stock among several smaller containers.
If you make a practice of chilling things often,
consider getting a blast chiller. A blast chiller is to
a refrigerator or freezer what a convection oven is
to a regular oven: it speeds heat transfer by
disrupting the layer of static air that insulates
food. Blast chillers have large, powerful fans that
move air across the food at high speed. They also
have large compressors to provide sufficient
cooling capacity. As the name implies, blast
Sensitive foods require special care to ensure their safety,
and ice cream is a classic example of what we mean by
“sensitive.” Most ice cream bases contain egg (which can
carry Salmonella or other contaminants) plus sugar and milk
(which create an ideal growth medium for bacteria). You
cook the base in a pot and scrape it down with a spatula that
perhaps has only been rinsed off, and then perhaps transfer
the base to a container that went through the dishwasher. To
do the transfer, you may pour the base through a fine-mesh
sieve—a tool that is exceedingly hard to clean.
From a food safety perspective, this is a recipe not for
dessert but for disaster. The problem with ice cream is that
chillers cool food to refrigerator temperatures very
quickly, and they can rapidly freeze food solid.
A challenge equal to maintaining consistently
low temperatures within a refrigerator is that of
trying to get a consistently accurate reading with
most available thermometers. Few cooks recognize
the dubious accuracy of thermometers; most
believe them adequate for keeping careful tabs on
temperature. Thus, they become lulled into a false
sense of security about the safety of their food. We
hope to dispel this complacency.
First, get rid of your analog thermometer; it
cannot be trusted. Sugar thermometers are fine,
and necessary for measuring high temperatures.
But analog thermometers are useless at low
temperatures, especially those temperatures
applicable to sous vide cooking. And delicate glass
is obviously not an ideal material to have around
food because it can so easily break. Equally
worthless are the classic meat thermometers with
a metal spike and dial. Often they are accurate
only to within 2.5 °C / 4.5 °F.
A digital thermometer is better, but be aware
that, even if it reads out to a single decimal place,
its design often limits its accuracy to no better
than plus or minus 1.5 °C / 2.7 °F.
This points to the difference between accuracy
and precision. You may probe a piece of meat
three times in three different places and get a
consistent reading on your digital thermometer
once it’s pasteurized, it will never be cooked again. When
we randomly screened food for the presence of fecal
bacteria, ice creams were among the most notorious for
testing positive.
To minimize that risk, we advocate pasteurizing ice cream
in a sous vide bag. Put the bagged ice cream base into a
water bath to partially coagulate the egg yolk, and then
leave it in the bag to age. Keep the base refrigerated until it’s
time to churn it, and don’t open the bag until just before
churning. If you have stabilized the base (as discussed in
chapter 15 on Emulsions, page 4·196), you can even freeze it,
then thaw and churn it.
each time; the reading is precise and repeatable.
The only problem is that it doesn’t necessarily
match the actual temperature of the meat. It’s
entirely possible to be precisely wrong every time.
Even fancy digital thermocouples are accurate
to no more than 1 °C / 1.8 °F. For higher accuracy,
your best choice is a platinum RTD (which stands
for resistance thermometer diode). Most water
baths now include a platinum RTD controller, with
an accuracy of 0.1 °C / 0.2 °F. The downside is that
these controllers are both fragile and expensive.
Domestic ovens tend to swing in temperature
and can be off by as much as 5% at any given point.
At 205 °C / 400 °F that 5% isn’t a big deal, but for
cooking something at sous vide temperatures,
such as 60 °C / 140 °F, 5% can be the difference
between safe and unsafe cooking. Ovens, therefore,
should never be used for very-low-temperature
sous vide cooking. They are simply unreliable,
with temperature swings that are way too big.
Further Reading
Arduser, L., Brown, D. R. HACCP & Sanitation in
Restaurants and Food Service Operations:
A Practical Guide Based on the USDA Food Code.
Atlantic Publishing Company, 2005.
Juneja, V. K. “Thermal inactivation of Salmonella
spp. in ground chicken breast or thigh meat,”
International Journal of Food Science & Technology,
42:12, 1443–1448; December 2007.
Juneja, V. K., et al. “Modeling the effect of temperature
on growth of Salmonella in chicken,” Food
Microbiology, 24:4, 328–335; June 2007.
Tierno, Jr., P. M. The Secret Life of Germs: What
They Are, Why We Need Them, and How We Can
Protect Ourselves Against Them. Atria, 2004.
U.S. Food and Drug Administration (FDA).
Food Code 2009. Available online at: www.fda.
gov/Food/FoodSafety/RetailFoodProtection/
FoodCode/FoodCode2009/
Properly organized freezers make it easier
to manage frozen food and to turn it over
on an appropriate time scale.
Vegetables generally keep best at
3–4 °C / 37–39 °F, whereas fish and
meats do best at 0–1 °C / 32–34 °F.
If you can consistently keep your
refrigerator at 1 °C / 34 °F or lower,
you can store most food cooked
sous vide for 30 days, according to
FDA standards. At a refrigerator
temperature of 3 °C / 37 °F, however,
the recommended length of
storage drops to three days.
206 VOLUME 1 · HISTORY AND FUNDAMENTALS
FOOD SAFETY 207