This article recently ran in Baking & Biscuit International. 

Reading Bakery Systems has fully automated the mixing process with their continuous mixing systems. The ultimate goal is to have systems running independently, without any need for staff intervention. And, while mixing may be among the most complex manufacturing processes in a bakery, today’s mixing technology is very close to this goal. “This is because, complex as it may be, the process consists of sequenced, measurable and controllable steps. Not only are the latest mixers controllable, but the control packages are rich in data to demonstrate the process is repeatable,” specialists from RBS emphasize. Integrated controls can already address decision points instead of an operator who requires training and experience. With fully automated mixers, “Quality and consistency are confirmed at the beginning of the baking process and not at the end of the process,” they add. Continuous mixing systems can take input from other parts of the line, such as hopper levels, operation status of downstream equipment, and data inputs such as temperature, and use it to automatically adjust the mixing system parameters to assure consistent production and product quality. 

With fully automated mixers, quality and consistency are confirmed at the beginning of the baking process and not at the end of the process.

Handling Materials

Bulk handling is a similar process for continuous and batch mixers, throughout every step of the mixing process: Dosing: The benefit of automated continuous mixing is that the accuracy of the recipe is guaranteed, at any given moment of the day, or season. “The dosing by metering equipment is critical to this step. It is important that gravimetric metering, not volumetric is used, to guarantee the high degree of accuracy needed. Loss-in-weight feeders are used for powders and pump and flow meters are used for liquid ingredients,” RBS explains. Solid fats, or delicate components (berries, for example) require more specialized equipment.

• Mixing: RBS has been perfecting specialty mixers based on the premise that no single mixer can be used to make all kinds of bakery products. This is why the American specialist offers five types of continuous mixers, each in 4 to 6 sizes, for different production volumes. The different models vary in shear applied, energy input, mixing properties, and other design factors. Selecting the correct type of mixer for specific products is the key to perfecting automated production.
• Discharge: Managing dough discharge from batch mixing can be a challenge; by contrast, this is not the case for continuous mixers. The dough exits the mixer in a ‘log’ or a steady stream of dough. “A knife at the discharge of the mixer cuts the log into manageable-sized pieces, so that they are suitable for transport on a belt. This dough can then go directly into the downstream forming equipment, eliminating the large dough handling equipment needed after the batch mixer to cut the dough into smaller, usable pieces.

Accurate process monitoring = automation

Process monitoring is instrumental in automating the mixing process. It enables the mixing system to make automatic adjustments that account for variations outside of the mixing scope. It outlines process variables, highlighting constant values and less stable parameters, for a deeper understanding of the process that supports further advancements. “Instantaneous variations should be ¼% for liquids and ½% for dries or less. Typically, a variation of more than ½% for more than 5 seconds will create an alarm for the operator. However, the system is self-correcting and these alarms are rare after commissioning,” RBS explains.

The actual variation required to define an alarm is an adjustable input. Usually, three levels of alarms can be set,
with timings that are preset by RBS during commissioning:

• Level 1: The parameter moves out of range. The system begins to self-correct.
• Level 2: If the system has not self-corrected within the time selected by the operation (usually 5 seconds), the alarm is activated. The system continues to self-correct, or the operator can intervene.
• Level 3: If the system has not self-corrected and the operator has not intervened after a set period of time (usually 15 seconds), the system will shut itself down until the operator restarts the system. This can occur when an ingredient cannot be metered properly (i.e., it runs out), when the processing line stops somewhere downstream, or when the hopper to the forming equipment fills up.

Automated mixing systems adjust the throughput to keep the hopper at a constant fill level, using a photo eye above it. They can also stop the process altogether if they receive a signal from downstream equipment that the line has stopped working.

Process parameters that are automatically monitored during continuous mixing and recorded also include:  ingredient rates vs. process value, ingredient temperatures and finished dough temperature, all mixer parameters, work input, total throughput, and dough total since the last changeover, RBS lists. “Any process condition the bakery wants to track can be recorded and saved to a database known as trending,” the specialist explains.

Currently, with a fully automated mixing system, an operator is only needed for a few minutes every hour. Their main task is only to address the occasional alarm and to observe the dough to confirm quality. This type of solution can answer ever-increasing staff shortage issues, a driver for its adoption rate. By comparison, batch mixing remains labor intensive.

A cost analysis and payback period

The initial investment in a continuous mixing system is higherthan in batch mixing. The total cost of the latter will depend on the level of automation of the batch mixing system and the dough capacity of the line. In an estimation that also factors the reduction of labor costs, the return of investment with a continuous mixing system is usually between half a year and two years, RBS calculates. Where applicable, “The initial investment is worth it with this payback, and the additional benefits continuous mixing offers including more consistent dough, less energy usage in ovens, lower safety and food safety risk, less dough handling equipment investment and more.”