The term quality is defined as fitness for purpose or as fulfilling the requirements for a particular process. The specification of quality varies according to the requirements of the process and the ultimate end use of the product. A quality test tries to predict the performance of the flour in later processing during baking.
Whiteness of flour is important quality attribute. Because flour colour affects the colour of baked products such as breads. It also indicates the amount of bran remaining in the flour after milling and the whiteness of the endosperm material. Type of wheat, microbial contamination and milling process employed also influence flour colour.
It indicates the amount of mineral matter present in the flour and is commonly considered a quality index for flour. High ash content depicts high bran in flour which has adverse effects in bread making quality
Some of the starch granules get damaged during the milling of wheat in to flour. Amount of damaged starch can be ascertained by subjecting the flour to polarized light under microscope. Damaged starch absorbs more water than the undamaged starch. Excess damaged starch results in excessive susceptibility of attack by alpha amylase resulting in sticky crumb and weak bread structure. Hard wheats generally have more starch damage than soft wheats, leading to increased water absorption.
Sedimentation test indicates gluten quality and bread making potential of the flour. Flour is suspended in sodium dodecyl sulphate or SDS to observe the way it coheres and settles.Hard wheat flours having high glutenin proteins show high sedimentation value as compared to soft wheat flours.
Rheological tests such as viscosity, elasticity, consistency and extensibility are used to predict baking performance and behaviors of the dough during processing before baking. These are measured with special testing instruments such farinogrpah, mixograph, extensograph, alveograph and amylograph.
It measures force or torque during mixing of small quantities of dough and is generally used as a physical dough-testing machine in cereal laboratories. It helps in predicting the amount of water to be added to flour to get a fixed consistency during mixing; measures mixing characteristics and also predicts baking performance.
It mixes dough with vertical pins and records torque either by a pen or chart paper or electronically. Torque during mixing is recorded by a torque transducer or by recording electrical output from the motor driving the pins and mixing traces similar to those recorded by the farinograph are obtained. Small amount of sample of 1-2 g can be used in new models. Both mixograph and farinograph are used to predict the dough processing properties and baking quality on the basis of assessment of the mixing traces. Disadvantage of this is that interpretation of the curves is highly subjective and depends on the 'feel' of the operator.
The Brabender extensiograph is used to measure the extensibility of dough. Dough of fixed consistency is shaped into a cylinder and allowed to relax for various periods of time at 30°C. The dough is fixed and stretched by a hook passing through the centre of the sample at constant speed. Flour with good bread making properties has good resistance to extension than the poor bread making flour. Good bread making flour requires a greater resistance to, although the extensibility of both flours is similar.