Cooking for Geeks: Real Science, Great Hacks, and Good Food (66 page)
Read Cooking for Geeks: Real Science, Great Hacks, and Good Food Online
Authors: Jeff Potter
Tags: #COOKING / Methods / General
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 (see
Foodborne Illness and Staying Safe
in
Chapter 4
) 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.
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. We’ll cover the necessary hold times for different kinds of foods later in this chapter, because the hold times vary depending upon the composition of the food.
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 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.
Sous vide cooking requires very little in the way of hardware: a heater to keep the water bath at temperature, and a vacuum sealer to package foods so that they can be placed in the water bath without coming into direct contact with the water. While the commercial tools can still set you back many hundreds of dollars, a DIY version can easily be made for less than $100, and resealable plastic bags can be used in lieu of a standard vacuum system.
One difficulty of sous vide cooking is maintaining a water bath at a precise temperature, +/– 2°F / 1°C. The early days of sous vide cooking used laboratory equipment designed to hold water baths at the precise temperatures needed for controlling chemical reactions, but as you’d imagine, the lab gear has the drawback of being expensive. We’re right on the cusp of a wave of new products targeted at the home chef who wants to cook sous vide, and while the prices might still be out of your reach, they’ll surely come down until at some point the “three-in-one rice cooker” (steamer and slow cooker, too!) will become a four-in-one rice cooker.
Industrial circulators.
These are lab-grade units that either are designed to be submerged into a container of water (e.g., hotel pans) or are enclosures with built-in containers. PolyScience is the most common manufacturer (
http://www.cuisinetechnology.com
), with new units costing around $1,000. Grant is also a common maker (
http://www.grantsousvide.com
). With luck, you can pick up a used unit at an online auction site for considerably less, but be aware that you’ll have no idea what chemicals or pathogens a used unit might have been exposed to. If you do go this route, a three-step wash seems to be the standard cleaning regimen suggested: run it in a bath of vinegar, then one of bleach, and finally one of rubbing alcohol.
Consumer sous vide products.
With the popularity of sous vide rising, a number of consumer products have recently been released or are in development that bring the cost of the hardware down to the $400 range, such as the Sous Vide Supreme. While still on the expensive side, as a piece of consumer kitchen equipment, it’s not unreasonable, and prices will inevitably fall. Given the versatility and usefulness of the cooking technique, definitely consider looking at this category of products. See
http://www.cookingforgeeks.com/book/sousvidegear/
for suggestions on current products.
DIY sous vide.
Other commercial products supply the “sous vide logic” but are
BYOHS
(bring your own heat source). Appliances like slow cookers contain the necessary cooking parts already: they hold a reservoir of liquid, have a heating element, and are designed to run for extended periods of time. You can repurpose them for sous vide cooking by adding an external controller that switches the slow cooker on and off to keep it near a target temperature. See the sidebar on making your own sous vide rig for details.
If you’re the type inclined to fiddle with electronics, you can build your own sous vide rig by ordering a few parts online and spending a few hours tinkering.
The actual electronics necessary to maintain a water bath at a set temperature are simple enough: a basic slow cooker, a thermocouple, and a simple thermostat controller to switch the heat source on and off.
First, the slow cooker.
The slow cooker will serve as the brawn, holding the water and providing the heat source. Snag a cheap slow cooker — you need one that will turn back on after losing power. Look for one that has a physical knob; the digital ones reset and stay off after power has been cut and then restored.
Next, the thermocouple.
If you have a standard kitchen probe thermometer (which you really should), the probe — long braided cable, metal probe — is a thermocouple. For a sous vide rig, you’ll need a type J thermocouple, which is made of materials that give it good sensitivity in the temperature ranges of sous vide cooking. This should cost around $15 to $20; search online for “type J probe” or search for part 3AEZ9 on on
http://www.grainger.com
.
Finally, the temperature controller.
Just about any thermocouple-based temperature switch will work; look for one that runs off 12 volts DC, such as Love Industries’ TCS-4030, which runs about $75. Snag a 12-volt wall wart (AC/DC power adaptor) while you’re at it.
Once you have all the parts on hand, it’s a relatively straightforward procedure to perform the lobotomy on the slow cooker: hook the thermocouple up to the probe inputs on the switch and connect the 12-volt power supply to the switch, then snip the slow cooker’s electrical cord and run one side of it through the switch. Create a small hole in the lid of the slow cooker and poke the thermocouple through. Make sure you use enough water in the slow cooker that the thermocouple makes contact with the water when the lid is on!
Regardless of what type of vacuum packer you use, make sure that the plastic bag you’re using is heat-stable.
Commercial in-chamber vacuum sealers.
The industrial vacuum sealers create a (mostly) air-free chamber (a true vacuum). Unfortunately, they cost thousands of dollars. Fortunately, you don’t need one. While there are a number of handy applications for them (
mmm
, watermelon steak), sous vide doesn’t require this level of vacuum seal.
Consumer vacuum food sealers.
These devices suck the excess air out of a plastic bag and then seal the bag by means of melting and fusing the opening of the bag. They don’t create a true vacuum (in the sense that the food isn’t subjected to a reduction in atmospheric pressure), but they do pull out most of the excess air. This is perfect for sous vide, because the function and purpose of the bag is just to allow rapid heat transfer from the water bath to the food via convection currents. Air in the bag would both slow the rate of heat transfer and also cause the bag to float in the water, preventing the face-up side of the bag from absorbing heat.
Resealable plastic storage bags.
Sealable sandwich and storage bags (e.g., Ziploc bags) are not safe for
boiling
food. The concern with boiling applications is the potential for the plastic to leach into the food. The melting point of the type of plastic used in these bags is only a few degrees higher than the boiling point of water. BPA (bisphenol A) contamination would also be of concern, especially if you are adding oils inside the food. Check to make sure the manufacturer of the bags you have does not use BPA.
SC Johnson, the manufacturer of Ziploc-branded bags, does not use BPA.
Sous vide cooking, however, does not boil the water. 170°F / 75°C is about the highest temperature you might use in sous vide applications; 140°F / 60°C is about the warmest that’s commonly encountered. Is 170°F / 75°C safe? SC Johnson is on record claiming that, yes, “[Ziploc] bags can be safely heated to 170 degrees Fahrenheit [76°C].”
Remember, the function of the bag is to allow heat to pass quickly from water to food via convection, so if you do use a plastic bag, make sure to remove as much air as possible. You can submerge most of the bag, leaving just the sealing strip at the top above water, and then seal it. Adding a bit of olive oil or marinade helps, because it’ll better conform to the shape of the food.
Douglas Baldwin is an applied mathematician at the University of Colorado at Boulder who, failing to find a good guide to sous vide, created his own, “A Practical Guide to Sous Vide Cooking,” available at
http://www.douglasbaldwin.com/sous-vide.htm
.
He is also the author of
Sous Vide for the Home Cook
(Paradox Press)
.
How did you hear about sous vide, and how did you get involved in it?
I was reading an article in the
New York Times
by Harold McGee, and he mentioned sous vide. While I knew quite a bit about cooking, I had never heard the term before and was intrigued. So I did what any good geek does: I went to Google and did some research. There was some information but not enough to meet my curiosity. So I turned to the academic journals and found a wealth of information.
It took me three or four months to collect and distill the 300 or so journal articles I found and publish the first draft of my guide online. I also did some calculations to figure out how long it takes things to cook and how long it takes to make them safe.
Safety is one of the big topics that comes up with sous vide and I’d love to talk about that in a moment. But first, what turned out to matter more than you expected when cooking sous vide?
People always worry about the vacuuming process, but that’s really the least important part, even though the name sous vide means “under vacuum.” It’s really the precise temperature control that is important.
Long-term precision is important, because you don’t want slow drifts when you’re cooking for days to cause your meat to be overcooked. But short-term fluctuations in temperature really aren’t that important because they will only affect the very outer portion of the meat. As long as the heat is oscillating less than one or two degrees Fahrenheit and the mean temperature is constant, you should be fine.
Wow! Cooking meats for days? What sorts of meats actually need cooking for that length of time?
Well, my favorite is beef chuck roast cooked for 24 hours at 130°F / 54.4°C. It’s delicious. It transforms one of the least expensive cuts of beef into something that looks and tastes like prime rib.
It’s all about the conversion of collagen into gelatin. This conversion is pretty rapid at higher temperature, taking only 6 to 12 hours at 175°F / 80°C to completely convert everything — well, almost everything. But at lower temperatures like 130–140°F / 54.4–60°C, it can take 24 to 48 hours for the same conversions to occur.
When I look at something like brisket being cooked at 130°F / 54.4°C for 48 hours, alarm bells go off in my head. Isn’t there a potential bacterial risk here?
Well, certainly there’s no risk at 130°F / 54.4°C. The pathogen that determines the lowest cooking temperature is
Clostridium perfringens
. Its highest temperature reported in literature is 126.1°F / 52.3°C. So as long as you’re above that temperature, there won’t be any food pathogens growing.
Now, there is the possibility of spoilage or beneficial microorganisms growing at these lower-cooking temperatures. That’s one of the reasons that some people will sear ahead of time or drop the package of vacuum-sealed food in a pot of boiling water for a couple of minutes to kill off any thermophilic microorganisms that might be in there, like lactobacilli. But, in terms of safety, there’s no concern whatsoever.
How about things like salmon, which are cooked at even lower temperature ranges than 130°F / 54.4°C?
If you would be fine eating the salmon raw, then cooking it for a couple of hours at a very low temperature, say 113°F / 45°C, isn’t going to be a problem. If you wouldn’t be comfortable eating it raw, then you probably shouldn’t be cooking it at anything less than pasteurization temperatures and times.
Most food scientists and food safety experts agree that you should pasteurize fish. Even though it may not taste the same, or possibly quite as good, at least you’ll feel a little more safe.
Food safety is about controlling both the actual and the perceived risk. Many people perceive the risk of fish to be much less than the risk of pork, but in many ways it’s probably the other way around.
In our modern agro-industrial complex, we don’t really know where things come from. With this decrease in knowledge of where our food came from, what field, how it was processed, and how it finally gets to our table, I tend to take the attitude of “pasteurize everything and hope for the best.” Though it may not be what everyone wants or likes to hear.
What are the risks and what can somebody in the kitchen do to partially mitigate those risks?
When you’re trying to deal with food safety, especially when it comes to pathogens, it is about three things. First, starting with a low initial level of contamination, which would mean buying, for example, very good and very fresh fish for which you know the origin. The second is to prevent the increase in the level of contamination and is frequently accomplished with cold temperatures or acids. The third is reducing the level of contamination, usually by cooking.
The problem is that if you’re cooking fish sous vide at only 113°F / 45°C, then you won’t reduce the pathogens to a safe level. So either pasteurize your fish by cooking it at 140°F / 60°C for about 40–50 minutes or make sure that very few pathogens grow and that the fish has a very low amount to begin with by buying from a trusted source.
Can one reduce the level of parasites by freezing?
Parasites, certainly. Though freezing fish at home will affect the quality of fish, because consumer freezers just can’t freeze the fish fast enough to prevent large ice crystals from forming. Now, it’s completely possible that you can buy already frozen, high-quality fish, or simply find out from your fishmonger whether or not it has already been frozen for a sufficient amount of time to kill any parasites.
But freezing won’t kill the different bacterial food pathogens that one might be concerned with, and there’s always the concern of chemical contamination, especially with shellfish that are harvested from questionable waters.
How do you know if something will work when you go to sous vide it?
I never really know, but I like to really scour the research journals for clues to the underlying processes involved. I first look to see if anyone else has already done it. With the wealth of scientific knowledge now available to us through the Internet, it’s very likely that someone has asked and answered a closely related question. Then I just try and adapt it to the home kitchen.
It always surprises me how often I can take things directly from an academic journal and apply them in the kitchen.
