Size reduction is an important unit operation carried out for reducing size of large size agricultural produce in to small pieces to facilitate further processing operations. Besides agricultural processing and food engineering field, size reduction operation is carried out in chemical, pharmaceutical and also in mining industries. Size reduction operation is also known as comminution, diminution or pulverization.

Why size reduction is an important unit operation?

Raw materials/ agricultural produce often large in size and therefore it should reduced in size so that they can easily handle during further operations. By reducing size of raw food materials subsequent processing become easy and final product become more handy and can made in different forms.

size reduction
Photo by Andre Taissin on Unsplash

Benefits of size reduction

  1. Size reduction increases surface area.
  2. Mixing of many ingredients can be carried out uniformly and easily.
  3. Appearance of final food product can be improved by reducing particle size.
  4. In case of emulsions, stability can be increased by reducing size of oil globules.
  5. In case of fruit beverages, size reduction of fruit pulp produces finer particle size. It reduces rate of sedimentation.

Methods of size reduction

There are numerous size-reduction equipment, developed to handle specific materials . Properties of raw material should be consider while selecting the proper equipment. In case of solid foods, hardness of raw produce is most important as in every size reduction method/equipment, energy required to create new surface area is proportional to hardness of raw material. Flow properties should also considered as in continuous size reduction operations, probability of choking discharge outlet.

Size reduction methods are as follows.

  1. Cutting: In this method, sharp and thin knife/cutting device is used to reduce the size of raw material.
  2. Crushing: In this method, external force is applied on raw material excess of its strength. By this, the material is ruptured in many directions and new reduced size particles are produced of irregular size and shape. Examples are: Food grain flour, oil from oilseeds, juice from sugarcane.
  3. Impact:  In this method, the raw material is introduced to rotating high speed hammers/bars.
  4. Shearing: Shearing process combines cutting and crushing method of size reduction. Shearing unit has knifes and bars to reduce the size of feed material.

Various size reduction equipment are hammer mill, plate mill, ball mill, jaw crushers, gyratory crushers, cutting machines (having rotating knifes), attrition mill etc.

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