The words sous vide literally translate to “under vacuum”, but it’s the meaning behind the words that matters. For instance, sauté is from the French, “to jump”, but the technique doesn’t strictly require aerobics, fun as they are.
So, the question we must answer is, “If your food isn’t ‘under vacuum’, is it still sous vide?”
Sous vide cooking is defined first and foremost by cooking at a precisely controlled temperature, typically at or slightly above the temperature you want the core of your food to reach. Although cooking in a sealed bag, in a water bath is a common way to cook sous vide, it’s not the only way. We understand that this might sound counterintuitive, so let’s explain.
There are lots of accepted sous vide scenarios that don’t involve a bag at all. A favorite technique among sous vide enthusiasts is to cook whole eggs right in their shell, where nature has done the packaging for us. Or, American chef Thomas Keller famously poaches lobster tails directly in a bath of circulating butter. Neither scenario involves vacuum bagging, but the results are unmistakably sous vide.
Food sealed in vacuum bags (usually) aren’t under vacuum at all.
A vacuum is a space that contains little to no air. Because vacuum bags are flexible, they bend around the food inside them, making tight contact. This doesn’t leave any empty spaces for a vacuum to form, so food inside a vacuum bag actually experiences normal atmospheric pressure. This is very counterintuitive, since wearestill removing air from the bag. But your food only experiences an actual vacuum in two cases: 1) if you’re using a rigid vacuum container (which is great for storage, but not great for cooking), or 2)duringthe vacuum process in a chamber-style vacuum sealer.
So why do we vacuum seal foods at all?
We often seal foods prior to cooking sous vide to avoid the food becoming waterlogged while immersed in water, if you’re doing cook-chill sous vide or you’re cooking in bulk with a plan to store bagged foods for later, or to hold a cooking liquid or fat close to the food — a marinade, a confit, etc.
This is why we use the term “sous vide” to describe the cooking mode in the Anova Precision® Oven: Your food may not be sealed in a bag, but it does experience very precisely controlled temperature during cooking. And that, for us, is the hallmark of sous vide.
Q&A About Bagless Sous Vide
Generally, no. That’s because traditional ovens only measure and control dry bulb temperature (with a normal thermometer). The Anova Precision® Oven directly controls wet bulb temperature — the temperature your food actually experiences — and maintains the temperature you set very precisely. Read more about the Oven’s Sous Vide Mode.
No, vacuum sealing is not necessary for sous vide. In fact — and this isverycounterintuitive — foods inside a sealed vacuum bag aren’tunder vacuumat all! A vacuum is defined as a space that contains little to no air [or matter, generally speaking]. Because vacuum bags are flexible, they bend around the food inside them, making tight contact. This doesn’t leave any emptyspacesfor a vacuum to form, so food inside a vacuum bag actually experiences normal atmospheric pressure.
If you’re using a chamber vacuum sealer — where the entire bag goes inside a rigid chamber — then your fooddoesexperience a vacuum as the machine reduces the atmospheric pressure inside the chamber before sealing the end of the bag.
You may notice, for instance, that foods with a lot of water start boiling during this process. That’s because the boiling point of water depends on the atmospheric pressure: the lower the pressure, the lower the boiling point (for a given temperature). But, once the bag is sealed and the machine releases air back into the chamber, the boiling stops. The food is no longer under vacuum, as the pressure of the atmosphere pushes against the bag, which pushes against your food.
However, there is one case where your food remains under vacuum — sealing in a rigid container. If you’re using a rigid vacuum canister, or you place a rigid container inside your vacuum bag, then the food is, indeed, under vacuum after sealing. Recall that a vacuum requires space with little to no air in it. The rigid walls of the canister are what maintain this space, fighting against the pressure of the atmosphere outside.
The food safety rules for sous vide time and temperature that you’re accustomed to for water bath cooking apply just the same in the Anova Precision™ Oven. However, if you’re practicing cook-chill sous vide and plan to store your food long term, we do recommend vacuum bagging your foodbeforecooking in the Oven. Combined with proper time and temperature, this ensures that the contents of the bag are pasteurized and remain protected from outside contamination.
Vacuum sealing your food creates an anaerobic environment — an environment that lacks oxygen. This inhibits the growth of certain spoilage bacteria, which is why we always recommend sealing your food before doing cook-chill sous vide. However, the spoilage bacteria of interest operate on longer time scales than you’ll experience for the vast majority of Oven cooking. So, sous vide recipes are safe to translate into their bag-free variants in the Oven. So, sous vide recipes can be safely translated into their bag-free variants in the Oven. However, if you are concerned about oxidation, or are doing very long cook times, following hygienic practices and pre-sealing your food before cooking in the oven will minimize risk.
The inside of a sous vide bag quickly rises to 100% relative humidity during cooking — in a water bath, or in the Oven. As the food in the bag heats up, some of the food’s water evaporates, quickly saturating any air remaining in the bag. So, all bagged food experiences 100% relative humidity.
In the Anova Precision® Oven, you can replicate this environment by using Sous Vide Mode and setting the Steam target to 100%. The Oven will fill the cavity with humid air, replicating the 100% relative humidity conditions in the bag. However, you also have the ability to set the oven to a lower relative humidity while still maintaining the same wet bulb temperature. This is useful for cooking skin-on poultry and other foods for which you want the surface to remain dry for better crisping or browning.
Foods cooked sous vide in vacuum bags lose juices as well — your sous vide steak typically sheds some juice into the bag during bath time. The same is true in the Oven. But with the Oven set to 100% relative humidity, those juices will collect in a pan, so you’re free to retain them for use in a sauce or gravy. However, if you want to keep your food immersed during cooking in a marinade, sauce, or a fat, sealing your foods in a bag will help maximize surface contact.
A great reference for in-depth information related to sous vide, food safety, and vacuum sealing is the book series, Modernist Cuisine: The Art and Science of Cooking.