What is Oven Humidity?
Oven humidity can be expressed as either relative humidity or absolute humidity. Both of them are the measurement of the moisture in the air. Relative humidity is ratio of the partial pressure of the water vapor in a mixture to the saturation pressure at the same temperature. The higher the relative humidity, the more moisture is available in the surrounding air.
Absolute humidity is the measure of water vapor (moisture) in the air, regardless of temperature. It is expressed as grams of moisture per cubic meter of air (g/m3). Different humidity sensors might express oven humidity in different units but it is important to note that at oven temperatures, or any ambient conditions greater than the boiling point, measurements must use the Absolute Humidity algorithm.4 Relative humidity is an inappropriate unit of measure above 1000C (2120F).4
What can oven humidity influence?
Oven humidity influences the two important dynamic processes during baking: the energy (in the form of heat) transferring into the food, which causes starch gelatinization, enzyme reaction, etc., and the moisture migrating from the product interior to the surface and evaporating. The concentration of water vapor within the oven also affects the rate of heat input into the dough.1
Baking parameters influenced by oven humidity
- High oven humidity can lighten baked goods crust color.2 That is because the increasing humidity blocks the direct temperature transmission to the product. So the crust temperature during baking is lower and the product color is lighter.
- High humidity increases baked goods volume.1 The reason is that the water loss from baked goods decreases with increasing humidity, and the product rises more before the crust sets.
- High humidity raises the final moisture content of baked product, which influences product shelf life and breakage during the packaging process.
- Reduced evaporation can keep the surface of baked product moist, allowing it to stretch and preventing cracks.
- Some products require surface condensation to produce a concentrated sugar solution, which gives the surface a glaze like the top of a brownie. Higher humidity will result in a glossier surface.
Factors that influence oven humidity
- Load of the oven: Humidity inside the oven increases as more products enter the baking chamber, and humidity will finally reach equilibrium. Simultaneously, heavier loading requires more heat to evaporate the water, resulting in a slight temperature drop in concert with the humidity increase.
- Temperature: Absolute humidity is lower on average at low temperature than at high temperature, because water evaporates more rapidly at higher temperatures.
- Saturation level of steam and the amount of steam used in the oven
How to measure oven humidity
A humidity sensor can be used to measure oven humidity at product level and with the oven under full product load. It can also be used to document the relationship between oven moisture and finished product moisture.
How to control oven humidity
- Use fans and dampers: The humidity in existing ovens is usually controlled by fixed-speed extraction fans and extraction dampers. The humidity on new ovens is usually controlled by variable-speed extraction fans.
- Use perlite: Perlite is a porous, expanded, natural volcanic glass. It is used to make dummy loads that increase oven humidity. In one study, about 90 g dry weight of perlite was used, with 365 g distilled water added to it for cake baking, and 320 g for bread and cookie baking.3
- Control the water level of the steam used for the oven.
- Do not overload the oven.
The following graphs show the difference in oven humidity with the damper open or closed:
- Xue, J., and C.E. Walker. “Humidity Change and Its Effects on Baking in an Electrically Heated Air Jet Impingement Oven.” Food Research International, vol. 36, no. 6, 2003, pp. 561–569.
- Schirmer, M., et al. “Impact of Air Humidity in Industrial Heating Processes on Selected Quality Attributes of Bread Rolls.” Journal of Food Engineering, vol. 105, pp. 647–655.
- Xue, J., et al. “Effects of Oven Humidity on Foods Baked in Gas Convection Ovens.” Journal of Food Processing and Preservation, vol. 28, 2004, pp. 179–200.
- Pearce, Ray. “RE: Relative Humidity.” Received by Katie Jones. 10 Feb 2017.