Sous Vide Cooking (part 3) - Sous Vide Hardware

2. Sous Vide Hardware

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.

2.1. Water heaters

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-inone 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.

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.

2.2. Vacuum packers

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.

Note:

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 on Sous Vide

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.