Continuous mixing creates a very homogeneous dough.

Continuous mixing creates a very homogeneous dough.

Continuous Mixing


What is Continuous Mixing?

Continuous mixing feeds dry and liquid ingredients continuously into a mixer via automated metering systems. This system delivers ingredients into the mixer at one end, while producing a continuous stream of dough at the discharge end.

Under the concept of continuous mixing, quantities of ingredients change from a per-batch, or load basis, to a per-minute, or per-second basis.

Origin

The continuous mixing method was introduced in the United States in the 1950s. The most common systems were Do-Maker and Amflow, both now replaced by high-intensity batch mixers. The continuous mixing technique was developed to meet the needs of bakeries operating in batch mode. Batched doughs often present problems associated with batch cycles (i.e., inconsistencies among batches due to processing variations and controlling mechanisms).1

How does continuous mixing work?

This type of mixing is a form of mechanical dough development that has two components; a premixer and a developer.

Premixer

In this stage, dry and liquid ingredients are fed into the premixing chamber for even distribution of water and initial hydration of the flour and other dry minors and micros. In the case of preferments, the liquid preferment or brew is pumped into the premixing chamber, where the remaining flour and other ingredients are metered in. The premixer has an endless screw or auger that provides the initial blending of the dough. The mixture does not increase in temperature while in the premixer.

Developer

A slow-moving auger in the premixer moves the dough into the developer, an enclosed mixing chamber or barrel usually jacketed for temperature control. The developer takes the place of conventional horizontal and vertical mixers, as it mechanically develops the dough using endless screws or augers. As the dough is pushed through the disks, it is developed and aerated. Dough temperatures usually reach 90–100°F (32–38°C). High-speed rotating screws, moving up to 300 rpms, bring about rapid dough development. This pressure, high friction and shear force from the high rpms generate the high-temperature dough.

At the end of the developer, the dough is extruded, cut into fixed-size loaves, and deposited directly into a pan. The scaling weight is determined by the rpm of the developer, along with the cuts per minute.2

Application

Continuous mixing units are commercially available, but only a small portion of large-scale baking plants use this technology. It can be employed to produce bread, rolls, buns, hard biscuits, crackers, and cakes.

Continuous mixers have several advantages and disadvantages:

Advantages Disadvantages
  1. Enclosed equipment components can be cleaned in place
  2. Continuous mix system requires less equipment and space
  3. Labor and energy costs are reduced
  4. Has excellent scaling accuracy due to the high-tech dry and liquid ingredient metering systems
  5. Uniform finished product with a fine crumb grain
  6. Does not produce  the “beginning or end of dough” effect
  7. Reduces chances of product contamination (due to its closed equipment nature)
  1. High initial investment cost
  2. Reduced flavor and aroma intensity (depending on the formulation used)
  3. Finished product lacks crumb strength (depending on the formulation used)
  4. Continuous mixers are best suited to production lines running dedicated or very limited product ranges
  5. Changeovers may be  difficult and expensive

 

References

  1. Cauvain, S. “Mixing and Dough Processing.” Technology of Breadmaking, 3rd ed., Springer International Publishing, 2015, pp. 115–116.
  2. AIB International. Bread Manufacturing Process, Distance Learning Course, “Module 08 – Dough System: Continuous Mix.” https://www.aibonline.org/Start-Your-Training/Baking/Baking-Foundations/Bread-Manufacturing-Process-Online, 2018.