How the science of heat transfer can help you cook efficiently

We love cooking, but more to the point — we have an obsession with efficient cooking. That’s why we’ve dedicated years of work to developing and honing tools like the Anova Precision® Cooker and Anova Precision™ Oven, bringing professional-grade techniques and technology to the home chef.

But what makes one cooking method more efficient or effective than another? Cooking is, in many cases, the simple act of transferring heat to food to make it safe to eat, or reach a more desirable texture/flavor. Oftentimes we’re hoping to do both of these things at once. From simple “old school” cooking techniques using just an open flame, to highly complex and modern appliances, a majority of cooking methods utilize just two simple elements to accomplish the task at hand — air and water in varying forms.

Air, water, and the way they move heat to your food are critical in determining the doneness and texture of your finished meal. Let’s take a closer look at how this is accomplished, and the differences in effectiveness when cooking with air, water, and all the steam in between.

Thermal Properties for Cooking: Air vs Water vs Steam

Dry Air:

• Air gains and loses heat much faster than water. Because of that, a relatively tiny change in the power of the heating element in an oven causes a bigger temperature change than an equivalent power change would in a water bath. 
• Dry air is a weak conductor — undisputedly the least efficient of the group we’re considering in this blog post. An oven filled only with dry air will heat food much slower than an oven containing humid air, steam, or water vapor. 
• A convection oven uses a fan and exhaust to circulate hot air around the oven's cavity. Because the air is in constant motion throughout the cavity of the oven, this helps food to cook more evenly and efficiently.  

Water: 

• Water is far more efficient (23.5 times more, to be exact) in transferring heat than air. Given a specific volume of water flow over a hot component (the volumetric flow rate), water has a heat carrying capacity nearly 3,500 times that of air.
• Because water and other liquids are so much more dense (1000 times more dense) than dry air, convection in a water bath moves heat more effectively than convection in air. More density means more collisions between hot molecules and the food you’re cooking — which means more efficient heat transfer!
• This is why if you reach your hand into a boiling pot of water, you’ll instantly suffer the terrible consequences, yet you could quickly put your hand into an oven cavity of hot, dry air at the same temperature without too much to worry about.
• Because the entire surface of your food is in contact with the cooking medium while heating, the same foods can be cooked for much shorter durations of time than would be required in an oven at the same temperature (212°F/ 100°C) with dry air.

Steam/Water Vapor: 

• Steam transfers heat much more efficiently than either water or dry air (approximately five times more effectively than water and around twelve times more effectively than air).
• Steam can be superheated almost without limit and releases a substantial amount of heat when it condenses to liquid water on the surface of the food you’re cooking. Because molecules of steam impart their energy of motion to the food as well as their energy of vaporization, steaming can quickly bring the surface of food up to high temperatures.
• A quick note on steam: True steam is invisible, what people are often seeing, and refer to as "steam", is actually water vapor.
• Because steam is more dense than dry air, it also does a fantastic job of filling and evenly heating the oven or vessel it is trapped inside.  

Leverage the science of heat transfer for perfect results

With all of the above in mind, we can then begin to think about how sous vide and combi oven cooking take advantage of these concepts to make the most efficient use of all factors at play in achieving perfect, repeatable results — every time. 

Sous vide: 

The concept of cooking sous vide is very simple: A standalone immersion circulator heats water and circulates it around the pot to maintain a very precise and even distribution of temperature for your desired amount of time.

The big problem with dry heat is that it transfers from the outside inwards, in uneven bands, leaving most of the steak’s outer layers at a temp well above the target while the inside may remain undercooked or below your target temp. When cooking sous vide, the entire steak is slowly brought up to, and never breaches, your target temperature. Sous vide cooking also circulates the surrounding water (aka uses convection) for the most even temperature distribution possible. The resulting food is cooked completely evenly to your desired doneness and only requires you to finish the outer layer with a nice sear for texture and browning. 

Combi oven:

A combi oven is, as the name implies, a “combination” oven. Combi ovens typically include both convection fans and steam injection, along with precise control of temperature, humidity, and convection fan speed. Above, we discussed the importance and implications of many of those properties — combining all of these features in a single appliance easily makes it one of the most useful single units you can own.

While an oven’s dry air on its own, as noted, is a weak conductor, the addition of a convection fan and exhaust changes the game completely. Air is in constant motion throughout the cavity of the oven, which helps food to cook much more quickly and evenly. And with optimal air flow (using a perforated cooking surface) you can easily achieve a crisp, air-fried exterior texture on your food.

To take things up a notch, you can then involve steam. It’s important to note that steam in this context doesn’t just mean “steam.” The Anova Precision™ Oven lets you control the level of steam or humidity independently from temperature. On a stovetop steamer, you get one setting: full steam at 212°F / 100°C. But with the Precision™ Oven, you can add as little or as much humidity as you’d like over the full temperature range of the oven. Not only is steam hotter and more efficient than cooking with dry air, but it also helps to retain the natural moisture of foods while cooking — hello juicy proteins and vibrant vegetables. Moist air also smooths out temperature swings, much like cooking in a water bath.

The ability to add and take away variable amounts of hot air, convection energy, and humidity within the cavity of a combi oven allows for dialing in the most efficient environment for cooking just about anything that doesn’t require something like an open flame. (You can even utilize settings to cook sous vide in the oven without the use of a vacuum seal bag.) It’s for this very reason that they’ve been an indispensable secret in professional kitchens for years, and why we knew we had to bring them to mainstream home kitchens.

Choosing the method that’s right for what you’re cooking

The big question at least a few folks will be wondering at this point is, “So what’s the best cooking method for me?” And while this isn’t the answer most will want to hear, it’s the truth: The “best” method truly depends on the food being cooked and the desired end result.

At the end of the day we’re all individuals with unique preferences, but the important thing is understanding the ways and means of achieving the finished product you’re after. Our job is simply to provide the tools and resources for you to make that happen. If you’re feeling like you’re in need of some guidance or inspiration, our dedicated recipe pages are a great place to track down recipes to help you understand the ideal settings for certain foods and different levels of doneness. Follow them to the T, or use them as a basis to riff off of for your own take on things — we can’t wait to see the results.

Related Posts:

• Marinades Demystified: How, When, and Why to Marinate
  
• How Chamber Vacuum Sealers Unlock Modernist Culinary Techniques at Home
• How to use steam in the Anova Precision Oven
• Water Physics 101