What is particle size?
Also known as granularity, particle size is a quality control parameter of a cereal flour after it is milled. The particle size of granular materials is commonly referred to as diameter, which is usually measured by geometric methods (microscopy, or by sieving a representative amount of sample).1
The particle size of a given flour depends on the processing conditions at the mill. it allows for the classification of milled products such as:
- Semolina: Particulate material from wheat generally of a size such that no more than 10% will pass through a 180-µm sieve/screen (in other words, at least 90% of the milled particles should have a particle size greater than 180 μm).2
- Wheat flour: Particulate material from wheat generally of a size such that at least 98% of flour should pass through a 212-μm sieve (US Standard Mesh No. 70).3
Particle size correlates directly with other quality indicators of cereal flours. It helps milling and baking industry scientists and technicians to assess:
- Flour’s purity (e.g., content of bran and minerals)
- Rate and extent of water absorption (water binding capacity) of wheat flours during mixing/kneading
- Mechanical damage of starch during milling process
Particle size of a given wheat flour is an important physical parameter for bakeries. The following are a few example of the role of its in the baking industry:
1. Particle size’s role in hydration capacity (water absorption) of flours
Hydration rate and extent are greatly dependent on the granularity of the flour used. The finer (smaller) the particle size of a flour, the greater its rate and extent of water absorption. In contrast, excessively coarse flours produce low-quality breads, since dough hydration is limited and takes longer to complete.4
Finer flours provide a homogeneous, complete, and almost instantaneous hydration of the protein macromolecules vital for dough formation and development. As a rule of thumb, the coarser the flour particles, the longer the mixing time will be, thereby increasing power consumption of spirals/planetary mixers.
2. Particle size’s role in cake-making
High-ratio flours used in cake-making are an excellent example of how particle size affects the overall texture of a product.
A successful cake-making process depends on the surface activity of the ingredients used, and so increasing the surface area of the available starch becomes important in aiding stability of the batter. For this application, it is desired that the...