BAKING LINE AUDIT
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Metrology on baking and freezing lines The audit of a baking and freezing line is an important step towards the
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Improvements may address issues of product quality, productivity and energy consumption, all of which are often interrelated. Other issues may relate to specific risks such as the presence of acrylamide, a chemical contaminant resulting from reactions occurring at high temperatures and involving ingredients contained in the product recipe. This contribution provides a review of the issues encountered in the context of applications in the cooking and then in the refrigeration and freezing processes. The last section focuses on the challenges addressed by energy audits. Baking processes The baking of cereal products under industrial conditions takes place in batch ovens with automated loading or in conveyor ovens. Baking involves high-temperature levels (150/250°C) or even much higher for certain specialties such as flatbreads (up to 600°C) with humidity control in the ovens playing a key role in the final quality of the products; a bakery oven should be considered as much as a drying device as a baking device and many of the elements mentioned in this section can be applied to the case of product drying. Air humidity can be expressed in different ways. The most common is the concept of relative humidity, which expresses, at a given temperature, the ratio between the partial pressure of water vapor and the saturation pressure of water vapor.
This concept is poorly adapted to the context of a bakery oven because of the low values reached. Another quantity used is absolute humidity, which expresses the mass of water per mass of dry air. It is sometimes confused with the specific humidity (water mass per humid air mass) often used in climatology. In general, it is necessary to watch the units because confusions are frequent and are linked to the English and French definitions which use close adjectives (confusion between absolute and specific for example); it is thus advisable to be careful about the units of these quantities. Absolute humidity (expressed in mass of water per mass of dry air for the following) is a relevant quantity for monitoring the hygrometry of a kiln because it expresses a quantity related to a mass of dry air which is a conservative quantity in the sense that the mass of dry air entering is equal to the mass of dry air leaving. The dew point or dew point temperature is also a relevant quantity that expresses the temperature from which the humidity of the air will condense on the products placed in a given environment; this quantity is usually expressed in degrees Celsius and it is easy to link this temperature to the air humidity. The absolute humidity in an oven varies greatly during the baking process. In general, high humidity is sought at the beginning of baking in order to ensure condensation on the surface of the products; this condensation will ensure the plasticization of the envelope of the dough that
METROLOGY ON BAKING AND FREEZING LINES
continuous improvement of production tools.
