What is Oven Humidity?
Oven humidity is an important variable in baking operations. Along with time, temperature and air flow (in convection ovens), it is used to better control the baking step.
- The temperature in an oven is higher than the boiling point of water (212°F or 100°C at sea level) and far beyond the temperature range where moist air can be modeled as a perfect gas.
- So, humidity inside the baking chamber cannot be measured as relative humidity.
- Instead, the absolute humidity concept or humidity mass ratio is used.1,2
How does oven humidity work?
Baking chamber moisture, a function of drying and a product of combustion, is defined in terms of mass of moisture relative to the dry air present (Lb water/Lb dry air). Or, as dew point: the temperature at which moisture in the air condenses on a surface.3
Humidity in an oven influences the 2 transport processes that take place during baking:
- Heat transfer: the energy, in the form of heat, is transferred into the product and causes dough/batter temperature to rise. This is reflected in physicochemical changes such as water/ethanol evaporation, expansion of gases, starch gelatinization, protein denaturation and Maillard browning.
- Mass transfer or moisture migration: due to the drying nature of the baking step, water migrates from the product interior to the dough surface. Evaporation in the baking chamber increases the hot air humidity. The amount of water vapor inside the oven also affects the rate of heat input into the dough or batter.
Baking parameters influenced by oven humidity
- Crust color: High humidity lightens the crust color of baked goods. This is because excess humidity blocks direct transfer of heat to the product. In addition, the condensates formed on the dough surface act as a natural insulation to heat transfer. Under this scenario, crust temperature during baking is lower than the target resulting in light-colored finished product.
- Dough expansion and product volume: High humidity increases the volume of baked products. A baking chamber rich in moisture decreases the driving force for water migration. So, less water is lost from the product to hot air, causing dough/batter to remain moist to expand/stretch further before the crust sets.
- Moisture content: High humidity raises the final moisture content of the baked product which influences product shelf-life and sliceability.
- Crust character: Some artisan and hearth breads require steaming to generate surface...