TThis article, is Sous Vide Cooking Safe?, was last updated August 2018.
Sous vide is becoming a more and more popular cooking method. Its reputation for making perfect steaks, meltingly tender pork butt, and juicy chicken breast has made millions of people eager to try it--and they haven't been disappointed.
Yet some people have misgivings about cooking sous vide. One reason is the expense: a lot of home cooks are unwilling to invest in an entirely new infrastructure in which they may not see a lot of advantage.
Another reason is just the inherent lag time that new technology always faces: is it a fad? or is it here to stay? Many people adopt a wait-and-see attitude before they decide to jump on the new technology bandwagon.
But I think one of the biggest reasons people are reluctant to try sous vide is because they're concerned that cooking sous vide isn't safe. Using low temperatures to cook vacuum-sealed food seems like you're just asking for food-borne illnesses.
And what about all that plastic?
These are the three primary safety concerns with sous vide cooking that seem to get brought up on food forums and modernist cooking blogs over and over again: low temperatures, vacuum sealing, and using plastic bags for cooking.
How justified are these concerns? Let's look at each one and see what we come up with.
First of All, What Is Sous Vide?
Sous vide is a French term that translates as "under vacuum." You can cook in a sous vide machine by using the water displacement method--lowering the bag slowly into the water and letting the water pressure push the air out of the bag--but sous vide was originally used only with vacuum sealed food.
A vacuum sealer not only removes more air, it also makes food easier and safer to store before, during, and after cooking it sous vide. (I have a lot of articles about this, including: Why Every Kitchen Needs a Vacuum Sealer and How to Save Time, Money, and Food with Your Sous Vide + Vacuum Sealer).
Restaurants have been using the sous vide method for decades. It provides an easy way to bring food to precise temperatures and leave it there until it's ready to be plated--no overcooking, no drying out.
Sous vide has been around for a long time, but it really caught the public's attention in 2011, when Modernist Cuisine came out. This book was the first real champion of the sous vide method and was the beginning of home cooks becoming interested in using sous vide. Yet the method has been slow to catch on, despite the large number of inexpensive immersion circulators that have entered the market in recent years.
A big part of that is concerns about the safety of sous vide.
Concern #1: Low Temperature Cooking
Concerns about cooking food at low temperatures is justified. If food is left for more than a few hours at danger zone temperatures, bacteria can grow and result in food-borne illness. For this reason, it's important that home chefs understand what the danger zone is and how to avoid it when cooking with sous vide.
What Is The Danger Zone
The Danger Zone is the temperature range at which bacteria grow most rapidly on food and cause it to spoil. This temperature range is 39F-140F (4C-60C). Foods most susceptible to bacterial growth at danger zone temps include meat, seafood, eggs, sauces, raw sprouts, and cooked vegetables, beans, and pasta. Food should not be left at danger zone temperatures for more than 2 hours.
Thus, food should be stored at temperatures below 39F, cooked at temperatures of 140F and above, and not left at anything in between for more than 2 hours.
Wait, you say. A medium-rare steak is 130F-135F, isn't it? Yes, that's true. And here's why it's safe to eat: there is a lot of buffer built in to the food safety standards. The truth is that nearly all bacteria--and all known pathogenic bacteria--is killed at 131F. This is according the FDA's "Bad Bug" book. So you can leave food in water baths set at 131F and above for several hours without danger of bacterial growth. (And I can attest to this from personal experience: I've cooked hundreds of steaks at 132F and have never once gotten ill.)
If you want to be extra safe, longer cooking times will kill more bacteria, as will cooking food above 140F.
For most people, food doesn't need to be fully pasteurized in order to be considered safe. We eat raw and raw-ish food all the time (medium rare steak, for example). However, some people need to be careful about consuming raw-ish food. If you're concerned about eating raw or undercooked food (pregnant women and immune-compromised persons have to be careful, for example), you should make sure sous vide food has been cooked either above 140F or long enough to be fully pasteurized.
How long does it take to pasteurize (or at least to make food completely safe to eat)? It varies. For most cuts of meat, at temps below 140F, it's a minimum of 30 minutes. Note that this time means the entire cut of meat must be at the set temp, so the 30 minutes should be added to the come-up-to-temperature time. How long is this? At least 30 minutes from the time you immerse the meat, and maybe longer depending on how thick the cut is. how cold when you put it in, etc.
How to avoid the danger zone:
- Store food at temperatures below 39F
- Cook it at temperatures of 131F and above
- Not leave it at any temperature in between for more than 2 hours.
How Do I Make Sure My Sous Vide Cooked Food Is Safe from the Danger Zone?
That's simple. Just follow these rules:
- Cook food at 131F and above, giving it enough time for the internal temp to reach this point and stay there for at least 30 minutes.
- Or, if you cook food below 131F (such as salmon, which is going to be dry and overcooked at 131F), be sure to not leave it in more than 2 hours.
- Or, if you cook at 140F or above--such as for chicken, pork, and tough cuts of meat--you pretty much don't have anything to worry about as long as the entire piece of meat reaches temps of 140F or above.
That's it; that's all you really need to do to avoid food-borne illness from sous vide cooking.
In reality, the chances of contracting a food-borne illness from sous vide cooked food is probably about the same as from any other cooking method, as long as you follow danger zone precautions. And as with all cooking, safe handling is very important: always wash your hands before handling food, avoid cross-contamination, wash food before using, etc.
Concern #2: Vacuum Sealing
Vacuum sealing creates an anaerobic environment, which is the ecosystem preferred by one of the most toxic and dangerous food-borne pathogens: botulism.
If you combine food sealed in an oxygen-free environment, then cook it with warm-but-not-hot temperatures, aren't you just asking for botulism? Again, that depends mostly on how careful you are about danger zone issues...
What Is Botulism?
Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum. (Note: it is not caused by the bacterium itself.) The most common cause of botulism in adults is improperly preserved food.
In fact, botulism is extremely rare in developed countries. According to Wikipedia, there were fewer than 200 cases of it in the U.S. in 2015.
If you're concerned about food safety in general (and if you cook, you should be), there's a lot more to know about botulism and how to avoid it. This Wikipedia article is a good overview for anyone interested in food safety. There is also a lot of great information about food-borne pathogens in Volume One of Modernist Cuisine (linked above).
Botulism and Vacuum Sealing
Botulism is certainly possible under anerobic, low-temperature conditions. However, if you follow the precautions for avoiding danger zone issues, then you are most likely safe from botulism, as well.
Here's an excerpt from a cooking forum discussion about it:
Sous Vide and Botulism
If done properly--that is, adhering to proper times and temperatures--sous vide cooking is safe. However, there IS botulism risk from improper sous vide cooking. Clostridium botulinum is an anaerobic organism. It grows when there isn't oxygen; environments like vacuum-sealed bags and canned goods can be ideal candidates for the organism.
The sous vide method cooks without oxygen and at temperatures close to those needed for the botulism organism's perfect reproduction rate. If you cook it a little lower than recommended, you could be creating a perfect place to reproduce. Clostridium botulinum dies around 126 F, and most bacteria die at 130F and below. So most sous vide recipes recommend not going lower than 131 F--or if so, not cooking for more than two hours at temps below 131F.
Sous vide opponents state that the temperatures in general are far too low to be safe. And if we were cooking for just a few seconds, it would be. Luckily, pasteurization is a function of temperature and time. This is part of the sous vide magic. Bacterial death is a result of heat and time - if you have a high heat you may only need it for seconds. If you have lower, but sufficient heat, then as long as you cook it long enough (see recommended reading below) - then the food still gets pasteurized. Sous vide often cooks foods for hours and hours - either for taste and/or for pasteurization. (excerpted from: https://cooking.stackexchange.com/questions/18632/are-the-claims-legitimate-linking-botulism-to-vacuum-prepared-foods)
For information on cooking times for meat, see Sous Vide Time and Temperature Charts for Proteins.
This explains the situation very clearly. So, yes: botulism is possible with vacuum-sealed, sous-vide cooked food. But if you follow the rules for the danger zone, then it is extremely unlikely to be an issue with sous vide cooking.
Concern #3: All That Plastic!
Cooking in plastic bags is probably the least attractive thing about the sous vide method. After all, aren't we all trying to cut down on our plastic use in an effort to reduce our carbon footprint? And isn't plastic dangerous, anyway?
I love cooking sous vide for so many reasons. But using plastic bags is not one of them. When I first started cooking with sous vide, I didn't like all the plastic I was going through. But sous vide is so convenient and the results are so great that I wasn't willing to stop using it.
The truth is, whether you use sous vide or not, you're going to go through a lot of plastic in the kitchen. Almost all the food we buy comes in some form of plastic wrap or container. We freeze food in plastic, we store food in plastic bags and containers. Plastic wrap, plastic bags, Tupperware, and Rubbermaid are all parts of pretty much everyone's kitchen landscape.
So in reality, using sous vide bags doesn't really add that much to our overall plastic use in the kitchen. But if you're concerned about it, as I was, there are some things you can do.
Ways to Reduce Plastic Use When Cooking Sous Vide
Here's what I've done to reduce my plastic use in sous vide cooking:
- I use the same bag for freezing as I do for cooking. When I freeze meat, I pre-season so it's ready to just pop into the sous vide for a couple of hours. (Bonus: This also simplifies meal prep!) Now, some people say it can toughen meat to freeze it in a bag with salt, but I haven't noticed any issues with it. If you do, just salt it after the sous vide cook and before finishing.
- I also use the bags for storage after cooking if there are leftovers. I always try to seal as close to the top of the bag as possible so I can re-seal it for this purpose. You must be sure to chill quickly and make sure the food stays below 40F until ready to eat again--otherwise the anaerobic environment could be a problem.
- When possible, I use mason jars for sous vide. This isn't possible for a lot of foods because the water has to reach as much surface area as possible. However, it is possible for making foods like yogurt and creme brulee, which both cook really well sous vide. And eggs come in their own hermetically sealed package, so they don't require any container at all.
In addition, I also use mason jars for a lot of my food storage now, and I try to buy in bulk when possible to avoid a lot of plastic and styrofoam packaging. (You can find mason jars in just about any grocery store, but I've only been able to find these great reusable lids online.)
Because of the plastic concern with sous vide cooking, some companies are developing reusable silicone bags. I haven't tried them yet, and I'm not sure how well they'll work because they're probably a little too stiff to wrap nicely around the food. But be sure to check them out if you're interested.
If you're extremely thrifty, you can also just re-use your storage and vacuum seal bags--as long as you're very careful about proper cleaning and drying after use.
More Efficient Sealing
You can also reduce plastic waste by efficient sealing. With a lot of edge sealers, you have to insert 25% or more of the bag in order for the sealer to work properly. If you want to use the vacuum bag more efficiently, buy a sealer such as the FoodSaver FM2000, which uses less bag for the seal. (It's also under $100!)
Alternatively, chamber vacuum sealers (like this one) are a great option because you can put the seal pretty much where you want it. The bags are also thinner--less plastic--and cheaper. So while a chamber vac is more money up front, you'll save both money and plastic with it long term. (If you want more info, check out this review of commercial-grade vacuum sealers.)
Plastics Leaching Chemicals
In addition to the use of plastic in general is the concern about the safety of cooking in plastic bags. The biggest concern with using plastic bags is that when they're heated to certain temps, they may leach harmful chemicals like Bisphenol-A (BPA). People have gotten very savvy about this in recent years. Many have stopped using plastics in the microwave and re-using plastic containers for food storage. Many have even stopped using plastic water bottles because they can degrade if left too long in the sun.
Is this smart? Sure, particularly when talking about re-using plastic storage containers for food. I hate throwing away plastic containers, but it's really wise to not re-use these containers, at least not for food, and especially not for re-heating in the microwave.
And if you still can't quite bring yourself to throw out perfectly good cottage cheese and yogurt containers, at least throw them out when they start to develop scratches--signs of wear could mean the plastic has degraded to the point that it will leach chemicals into your food.
Having said that, nearly all food-grade plastic is now BPA-free, particularly plastics designed for food storage and microwave heating purposes. But plastic is a complex substance, and it may still have potentially harmful chemicals in it that can break down under high heat conditions. (Understanding all the science behind plastic, including the different types and at what point they may become unsafe for use, almost requires a chemistry degree.)
If that's a concern for me, then why am I not worried about using plastic bags in a sous vide cooker? Here's why: all sous vide is done at temperatures below boiling, and boiling temp (212F/100C) is the temp at which plastics will start to break down. Also, all sous vide bags--at least from reputable manufacturers--are BPA-free, and won't break down at sous vide cooking temperatures.
This includes vacuum sealer bags and zip-type food storage bags: both are BPA-free and both are considered safe for sous vide use.
For More Information
Here's a great web site with a short video about sous vide and plastics. This is a medical site, and it also goes into some detail about different types of plastics and what to know about them. This is from 2012, so it's a few years old, but still very good information.
Also, here's a short article from Modernist Cuisine about plastics and sous vide. This article is from 2013, so it also may not contain the latest information. But in all the research I've done, I have not found any concerns about cooking food in BPA-free plastic at sous vide temperatures. And I believe that the folks behind Modernist Cuisine, who are scientists first and food lovers second, would be up-to-date on the concerns surrounding sous vide cooking.
Why Vacuum Bags Are Better than Storage Bags
While we're on the subject of plastic bags, I'd like to put a plug in for chamber vacuum sealers. The current trend in sous vide is toward using food storage bags and away from vacuum-sealed bags. The only reason for this is that people don't want to invest in a vacuum sealer in order to use their sous vide machine, and people selling sous vide machines are eager to tell them they don't have to.
It's true that you don't have to invest in a vacuum sealer to cook sous vide. But here are a few reasons why you might want to:
- Vacuum bags are sturdier. This means they're less likely to leak and break down (e.g., seams give out) during long cooks (those more than about 8 hours)--and you will be doing long cooks, believe me!
- You can double-bag vacuum bags if necessary (again, helpful for long cooks); you can't really do this with storage bags
- If you go the chamber vacuum route, the bags are cheaper than storage bags
- Most importantly, you can freeze food with no worries about freezer burn for a very long time (much longer than with storage bags) and go straight from freezer to sous vide.
I have been a fan of sous vide for several years now. Along with some of the world's greatest chefs and scientists, and based on the most arduous research, I believe that sous vide cooking is safe. I encourage you to do your own research and draw your own conclusions. I hope this article will help with that.