Many variations can and will affect the purity of flour. Age and efficiency of equipment, design of mill flow, machine maintenance, and fluting/corrugation condition are all factors that millers must consider in order to mill efficiently and minimize contamination.
"Break releases are possibly the most important form of control that a miller adopts in his efforts to produce a flour with a high consistency and with a unique specification," said John Bunn, flour milling advisor at AWB Limited, Melbourne, Australia.
Break release is the term given to account for the amount of work carried out by fluted/corrugated roller mills and ensure that full efficiencies are attained in the mill. Monitoring break releases ensures the proper amount of stock is entering the mill flow to keep it in balance. An imbalance in the mill flow causes poor extraction, poor flour quality, higher milling costs and lower mill capacity.
Bunn said break releases are used to evaluate rollermill performance over a period of time; monitor the wearing factor of roll flutes; control the balance of the mill; provide a repeatable benchmark setting for specific grists in order to optimize mill performance; and control the release of semolina, middlings and flour from the whole wheat and/or bran particles during the early stages of milling.
In order to achieve optimum efficiencies of all machines within a mill, all sections of the mill should be receiving the correct amount of stock that it was designed to receive, Bunn said.
MONITORING BREAK RELEASES. Regularly checking and adjusting the break releases is very important. Bunn recommends that mills check, and adjust if necessary, its break releases every change of shift or change of grist, in addition to whenever a change has occurred in the mill such as roll change, sieve change or grist change.
Jeff Gwirtz, professor of milling at Kansas State University, Manhattan, Kansas, U.S., often teaches the mechanics of correctly checking break releases.
"Release data is of no value unless it is collected in a controlled uniform manner," Gwirtz said. "It requires training and commitment, taking into account those events, or conditions that could cause variation in test results."
Gwirtz said controlled extraction at the primary breaks (first, second and third) was critical to successful production of high quality flour. "These breaks are the most heavily loaded in the mill and establish the load to purifiers, sizings rolls, and the reduction system," he said. "The secondary breaks (fourth and fifth) are not responsible for contributing extensively to flour yield. However, recovery of fine middlings to the tail end of the reduction systems is critical for acceptable flour yields."
Before the test is run, check the stocks to ensure load is evenly split between the rolls and is distributed across the roll. The sample must be taken across the entire trajectory of the stock as it discharges from the roll (i.e. front to back), Gwirtz noted.
Whether the sample is collected at both ends of the roll, across the entire length of the roll or in the center of the roll, the sample must be collected in a consistent manner. "Train to ensure the same procedure and equipment is used each and every time, without exception," Gwirtz said.
Once the sample is collected, there are several options for working with it. The entire sample can be used, which prevents segregation but requires collecting comparable sample sizes and performing calculations to determine the percentage through the screen.
Using a constant, measured amount of sample prevents calculations and effects of variable sample size, but might cause unintentional segregation. "Every effort must be made to maintain the integrity and uniformity of the sample collected," Gwirtz said.
When sifting the sample, use a screen appropriate to the stock, select and use one screen with a size similar to that used in the mill and sift each sample the same amount of time.
Weigh the stock held over the screen to calculate the percentage through the screen. "Data and calculations should be immediately recorded for every test," Gwirtz said. "Data and comments must be legibly written and corrective actions noted immediately."
Release data can identify a host of process improvement opportunities, he said. But it is critical that observed variations are not due to differences in operator skill level, procedures, testing apparatus or environment, he explained. The test should reflect differences in wheat quality or roller mill characteristics. For instance, roll wear can create flat particles that are difficult to purify, he said.
"Variations in release can indicate problems with blending and tempering process as well as first-in-first-out bin performance," he explained. "While new mill designs attempt to eliminate these problems, it is appropriate to monitor the process to ensure desired results."
According to Bunn, the importance of break releases should never be underestimated. "(Break releases) are the miller’s tool to set up and maintain a control of the milling process," he said. "Break releases can provide a means to create a reproducible benchmark when analyzing a mill’s performance, especially when a new wheat type is being milled. They can also be used to monitor the ongoing wear of the roll flutes."