Why is Humidity Important in Cooking?

What is Humidity

Easily stated humidity is simply the amount of water vapor held in the air. Water vapor is the gaseous state of water. As the temperature of the air increases more water vapor can be held since the movement of molecules at higher temperatures prevents condensation from occurring. For a complete description on humidity see: What is humidity.

Lack of Moisture -Humidity- in Traditional Ovens is a major issue for many cooks--

Humidity can have a profound effect on how food cooks. Humidity is something that traditional ovens have no control over. Water molecules conduct heat much faster than air. Not only does humid air transfer heat more efficiently to food, cooking it more quickly, it also helps prevent the water in the food from evaporating, keeping the moisture locked inside. While dry heat in an oven can be a good thing when you want a deeply browned crust on a piece of meat, it can be a problem with many types foods which you want to keep the moisture in.

What is wet bulb and dry bulb temperature -- Why are they important in Cooking?

The wet-bulb temperature is the temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel.

Nathan Myhrvold calls wet bulb and dry bulb temperatures the most important concept in cooking that you never heard of. ”Dry bulb temperature is measured by a temperature sensor placed inside the oven. Wet bulb temperature is measured by a temperature sensor wrapped in a wet cloth (see How is Humidity Measured). The relative humidity can be measured by the two temperatures: the higher the wet bulb temperature in relation to the dry bulb, the higher the relative humidity.

Dry bulb temperature is measured by a temperature sensor placed inside the oven. Wet bulb temperature is measured by a temperature sensor wrapped in a wet cloth. The relative humidity can be measured by the two temperatures: the higher the wet bulb temperature in relation to the dry bulb, the higher the relative humidity.

Why is this important? As stated above because food, being comprised of mostly water, feels only wet bulb temperatures. Dr. Myhrvold gave this example in an interview to Food Arts magazine: In Chicago in the winter, your oven is baking about 20 degrees lower than it would at the same temperature setting in New orleans in the summer. The variations all have to do with wet bulb temperatures. As Scott Heimendinger, Modernist Cuisine's director of applied research in a note to "Food and Wine Magazine (see reference below) explains it, humidity has a profound effect on how food cooks. "Water molecules conduct heat much faster than air," he says, explaining that it's the same phenomenon that causes hot, humid weather to feel more oppressive than hot, dry weather. Not only does humid air transfer heat more efficiently to food, cooking it more quickly, it also helps prevent the water in the food from evaporating, keeping the moisture locked inside. "In the heat of a traditional oven, you dry out the exterior of your food before the interior," he says. That can be a good thing when you want a deeply browned crust on a prime rib, but it can be a problem with foods like potatoes, which is why you typically wrap them in foil before baking to capture the steam. (The steam function of a combi oven re-creates that effect.) 

Future Ovens will take into account Humidity

Nathan Myhrvold’s author of Modernist Cooking states that: "We cook our food using technology invented to bake bricks." Nathan says that "Water evaporating from the surface of the food carries away heat, leaving the food cooler than the surrounding air. Scientists call this temperature at the surface of the food the wet-bulb temperature (that is, the dry-bulb temperature minus any cooling by evaporation). The lower the relative humidity, the more evaporative cooling, so the greater the difference between the two temperatures.

Because most of the humidity in an oven comes from the food, adding food to the oven raises the humidity and, therefore, the wet-bulb temperature (see below) at the food’s surface. This means that bigger batches bake faster. Did you burn the holiday cookies last year? Blame your oven’s ignorance of its own humidity." Food, being comprised of mostly water, feels only wet bulb temperatures so there is a need to have both dry and wet bulb temperature readingsin an oven.

Precisely controlling the temperature and humidity of an oven means you can better control the actual temperature ofthe food inside it.

In CVap and Combi ovens evaporation is controlled by producing a vapor-laden environment that completely surrounds food with moisture, creating an opposing vapor pressure that prevents the food from losing or gaining too much moisture. Independent control of air temperature determines the texture (browning level or crispness) of your food product. Independent control of water temperature matches the vapor temperature of the cabinet with that of the food being cooked or held, thus creating an ideal environment for maintaining food temperature over extended time periods.

Why Humidity is Important in Baking Bread

Steam is what makes bread light and crusty. If you have ever baked bread in a traditional oven to promote the bakery-style results you would brush the unbaked loaves with water, or spritzing a fine mist directly into the oven. 

Humidity slows down the cooking process in bread. Moisture evaporates from the surface of the loaf, causing the uppermost layers of dough to dry out and become rigid, and gluten—the elastic, protein component of the dough—coagulates forming a crust. Humidity delays these processes, which then delays the formation of the crust. With the addition of steam to the oven, the vapor will condense on the cold, raw dough, leaving a film of water on the exposed surface. This additional moisture will then absorb some of the oven’s heat, thereby lowering the dough’s surface temperature. This in turn slows down the dehydration process and prevents the gluten from coagulating too soon—both of which keep the dough flexible for longer. Steam also helps produce a really crisp crust. When the surface of the dough reaches 180°F, the starches in the slowly forming crust start absorbing moisture. Steam plays a hand in crust color, too, and prevents it from burning. 

Humidity in BBQ

Cooking meats over an open low flame results in what barbecue experts call "the stall" (when the temperature does not rise or may actually fall). Some believe this stall occurs when connective tissue in the meat softens and fat starts to render. This does occur but does not appear to be the reason for the stall. . The stall according to Greg Blonder (amazingribs.com) is a consequence of evaporative cooling by the meat's own moisture slowly released over hours. As the temperature of cold meat rises, the evaporation rate increases until the cooling effect balances the heat input. The stall stops when 'unbound water' from the surface and just below is released. This helps produce a crust. 

Notes on stall from an egullet Forum

"I think that a better explanation of the BBQ "temperature stall" is wet bulb temperature. Basically, if you have a wet thermometer, it reads a lower temp than a dry one, due to evaporation (unless relative humidity is 100%)...Food mostly cooks at wet bulb temperature - until the outside is totally dry.... this would not happen inside a SV bag (or in a combi oven or CVAP oven in low temperature steam mode.) Yes we have done the experiment (sort of) - we have recorded temperature in meat cooked SV or in combi for long intervals and we do not see a stall. 

One of the reasons using sous vide after smoking meat produces such great results is that sous vide cooking is able to maintain an ideal temperature (wet bulb) throughout the cooking process with little loss of water.