Just like wheat producers who often face challenging and variable weather conditions, millers also confront similar situations in seasonal weather changes that can directly impact not only the efficiency of the mill itself but also the yield, protein content, and other qualities of the final product.
In an effort to minimize these impacts and to optimize the milling facility’s efficiency, what follows are some key actions to consider.
Some of the more notable items include: temperature changes, condensation issues, humidity changes, purifier efficiency, temper times, correct break release, roll conditions, evaluating sifter efficiency, and analyzing ash of the flour throughs.
This article is based on a presentation by Simon Tiedge, director of technical milling, with Miller Milling Company, Minneapolis, MN, (612-345 1204/Simon.Tiedge@millermilling.com), given at the 2023 International Association of Operative Millers’ (IAOM) Conference and Expo, Minneapolis, MN, April 17-21.
Simon started his milling career in Wiesbaden, Germany in 2004, as a feed milling apprentice at the Raiffeisen Feed Mill on the Rhine River.After completing the apprenticeship in 2007, he attended both the German and the Swiss milling schools before starting a technical milling career with Bühler in 2008. This position eventually brought him to Minneapolis in 2011 as head of milling technology for North America.
In 2017, Simon joined the Miller Milling Company as the director of technical milling.
IAOM members can view the presentation by going to llc.iaom.org/on-demand
Temperature and Moisture
The ambient temperature and even the temperature of the wheat itself will influence water absorption rates.
It can be a delicate balance as to whether the bran or endosperm portion becomes too wet or dry thereby creating conditions that can impact milling efficiency and yield.
In areas where temperatures may be consistently dry and very warm, such as in Arizona or New Mexico, managing moisture levels might be a little easier when compared to more temperate climate conditions which experience more dramatic swings in ambient temperatures and humidity levels.
Monitoring moisture levels in the wheat and adjusting tempering times accordingly become very important.
Other factors to deal with include:
• Humidity changes. High humidity levels also create challenges in milling soft wheat, especially during hot summer months in the South, because sifter efficiency is impacted, and the late break rolls may fill up with flour.
• Flowability of products. During a hot, humid day, a milling operator learns quickly which spout angle is too low and hinders flowability of products.
• Condensation. Condensation issues are another concern, especially during winter weather when cold wheat is being transferred into a warm mill. So, if the wheat is going to be warmed up, that heating process needs to occur at a very early stage to prevent excessive condensation buildup in the spouts throughout the mill,
If the wheat is extremely cold or nearly frozen and isn’t in storage for a long time, utilizing grain heating equipment, which can maintain accurate temperature settings, becomes imperative for various reasons.
Besides eliminating condensation, heating the wheat will improve grain cleaning efficiency, improve tempering and water absorption, reduce flour ash, and thus give mills better yields.
If there are fewer fluctuations in the grain temperature throughout the year, the equipment will require less adjustments to obtain consistent results.
In addition, while condensation and bran dusting issues are often overlooked, they can easily become acute in the product when high-humidity or high-moisture conditions exist.
Keeping Tabs on the Weather
There is no one-size-fits-all rule relating to how much water to use and for how long in tempering grain largely because seasonal weather conditions are not always consistent on a daily or weekly basis.
For example, a good practice is to make sure that the milling team knows the weather forecasts in a 12-, 16-, or 24-hour period.
If the temper time is eight hours for a soft wheat or 18 hours for a Kansas hard wheat, then, make sure the team understands what the weather forecast conditions will be during that 18-hour period.
If a rainstorm is coming through, it’s important to take that into account to reduce the risk of adding too much water.
Plus, if it’s a really dry, hot day, that is another key consideration when adding enough water to avoid falling below the moisture specifications.
Temper times need to be adjusted accordingly to accommodate for either wet or dry weather conditions.
The chief point is that if it’s too wet or too dry, such conditions impact the yield and bottom line of the mill.
It’s also important to make sure that water penetrates into the wheat as uniformly as possible on a cool day as it should on a warm day,
Whether dealing with temperature or moisture, the potentially diverse changes in wheat conditions are what pose some of the key challenges in the mill.
Being consistent in how the wheat is prepped, such as cleaning, tempering, and conditioning, at the start before being milled goes a long way towards delivering a consistent, final product.
Correct Break Release
Determining a correct or ideal break release is another important factor in boosting efficiency.
Like tempering, there isn’t one set rule to follow in selecting a correct break release.
Even if the startup head miller may be using initially a break release sheet that came with the milling unit, eventually figuring out an optimum break release for changing conditions and especially for new crop will become very important.
There’s a way of finding out how to change that break release, and the following are some factors to consider in pursuing an optimum break release:
• Type of wheat: soft, hard, or durum.
• Design of the break system (short or long).
• Design of the grinding system.
• The finished product specifications.
• The tempering conditions.
• Temperature and humidity.
Optimum Break Release Test
It’s a good idea to re-evaluate the break release twice a year with the goal of maintaining an optimum break release.
Much will depend on the type of wheat being milled (i.e., soft, hard, or durum wheat). These wheat classes all have completely different break releases.
Key questions to consider include:
• Does the design of the break system involve a short number of breaks or a long number of breaks?
• Are only single-high rollermills being used all the way through sixth break?
• Are double-high rollermills being used on the first and second break, as well as on the third, fourth, and fifth break?
• Is the goal to extract that starch or endosperm in a fast or slow way?
• Is the goal to produce a low- or high-ash flour?
Whether performing a more gentle or harder grind, the finished product specifications still are very important.
To help answer some of these questions against what may be faced in terms of temperature and humidity, an optimum break release test may help.
It’s really important to understand the optimum grinding pressure on the semolina producing passages, which is the first break through the third break. Usually, semolina isn’t coming out of the fourth break.
It’s important to make sure that the semolina passages are properly balanced to achieve the optimum break release result.
Of course, the target is to achieve the highest amount of semolina or finished product with the lowest possible ash, and that should be the key target of any grinding passage.
Figure 1 indicates a first break/second break release extraction schedule of 25%/55%, 25%/53%, 30%/50%, 30%/45%, and so on. That’s how the first and second breaks separated out.
Samples of the coarse semolina and middlings coming out of the breaks are then taken, and the amounts are recorded. Tests to determine ash content are then conducted.
Some millers collect material samples in tube-like devices directly under the roll nip and assess both break release and density, while others use longer scoops farther away from the grinding line for safety reasons.
Taking samples as close to the nip of the roll as possible helps ensure the entire product stream is caught and that the sample is representative.
Armed with that data from testing the samples, a miller can make an educated decision on what he or she thinks would produce the best break release schedule beforehand.
As Figure 1 shows, a total of nearly 74% of semolina is produced. That’s pretty good. That’s a lot of semolina coming out of that passage.
In this example, the 73.2% semolina yield with a .662 average ash content may represent the best choice for this break release example, and that is how you determine a break release, including to make sure that the passages after that aren’t over or under loaded.
This also is a good time to evaluate the condition of the corrugated rolls and to determine if any replacements are necessary or need recorrugating. Many corrugation companies can supply guidance/tools to evaluate roll conditions.
Sifting Challenges with Humidity
High humidity conditions hinder sifting efficiency.
For example, during a warm, humid summer, issues may arise when flour starts tailing over on the flour screens, and the flour also may start tailing over into the breaks.
Often, the tailings stick to the bran, and they don’t even make it to a flour screen. That’s part of the problem.
When entering the winter season, the sifter becomes much more efficient, but all of a sudden, specks on the flour may appear which shifts the focus to over sifting instead of under sifting.
If the humidity and temperature drop significantly, that’s when very noticeable changes start occurring in sifter action. Lower temperatures and humidity usually generate more effective sifting.
The flour passes through the screen more easily and provides higher ashes and more bran particles in the flour, if over sifting isn’t avoided.
In addition, high temperatures and humidity usually cause less efficient sifting action, lower yields, and a lot of carryovers in the grinding passages and also often into the break passages.
Sifter Efficiency Test
Conducting sifter efficiency tests can be very important in preventing over or under sifting, as well as helping to maintain a good balance in flour yield.
While there are several different ways to perform a sifter efficiency test, the one described here briefly reflects Miller Milling Company’s method.
These tests are important because sifter efficiency changes with temperatures and humidity conditions.
The procedure followed by Miller Milling, which works out well, involves taking a 100-gram sample of the last flour screens’ overs of each section.
What follows are some additional key steps followed in the procedure:
1. Essentially, the procedure takes the last overs that would go to a grinding passage, or most likely to a reduction passage, and then sift it for about a minute over the same flour screen normally used in that sifter.
Plus, a predetermined flour screen mesh size also can be used if a miller just wants to standardize the screen size for the entire mill.
The most important aspect is that a miller can establish a standard here.
2. The percentage of the throughs are then recorded, as well as the percentage of flour that’s still left in that product that went over a flour screen.
3. Shortly afterward, the flour ash of the throughs is analyzed in order to pinpoint the amount of ash coming from the reduction passage in the milling section.
4. Another step involves setting an ideal percentage range of how much flour should be left in those overages.
That may beg the question, why should there be any flour going over a screen? Well, the idea is to produce flour that’s preferably free of any specks and in a controllable manner.
If everything is allowed through, that will create an over sifting situation, so this might force unwanted particles through the screen and that will remain there for a long time.
5. Normally, steps 1 through 3 are repeated every month and based on those findings the flour screens are then adjusted accordingly.
Examining the Ash
Ash curves also can help pinpoint potential issues with over or under sifting and aid in identifying exactly which passage or passages might be causing issues and subject to under sifting.
At this point, the actual ash amount of that section should be examined.
If the ash is already high, a miller might want to increase that percentage number, but if it’s already a low-ash flour and free of specks and with a high carryover of flour, then opening the screens may be warranted.
It’s important to be careful when opening the screens. In short, don’t open all of them at once but instead start with a couple screens at a time, depending on how aggressive or measured a miller wants to be in opening the screens.
For example, the first couple of screens might start going from 118 microns (µm) to 125 µm, or from a 118 µm to a 132 µm opening on a second couple of screens.
This exercise can lead to a point that lies somewhere in the range. Now, once that range has been established, it can be determined for the other passages.
At first, it sounds like a lot of tedious work. It can be. However, once a range has been established, the task becomes less burdensome. This data also is inputted and organized on an Excel spreadsheet.
While the sampling doesn’t have to be done throughout the shift, conducting the sampling itself every two to three months is probably a good idea.
It’s definitely a good practice to take samples when or just before a season changes. Sifting out the samples also can be done in some free time.
Image shows an example of a data sheet used at Miller Milling Company.
Numerous items are recorded, such as the weather of that day, the temperature, humidity, the mill’s total daily yield; what kind of flour was produced, and the wheat quality.
Weather and milling data were collected to build a data sheet to stay educated on the ideal mill screen change.
Changes in milling passage and actual screen sizes are recorded, as well as what was used previously.
Make sure the flow sheets are updated accordingly. It’s very important, because nothing frustrates a miller more than a flow sheet that’s inexact.
This data also reflects sifting and the ash data, as well as the target range settings for each of the sections in that particular mill.
With numerous data points, a miller can start to embrace the bigger picture. The miller isn’t operating in the dark, and it takes much of the guesswork out of the equation.
But embracing the bigger picture doesn’t happen overnight. Consider this exercise as a marathon, not a sprint.
The key aspect is to start recording this information in an organized way on a consistent basis and commit it to Excel spreadsheets.
Over time, this data becomes an invaluable reference library based on past experiences that can be utilized to make better educated decisions on what adjustments may be necessary to fine-tune the mill when seasonal conditions occur.
Purifiers should be examined when the weather changes because most purifiers receive product from the breaks or from the sizing throats. So, when the temperature/humidity changes, temper times and break releases also will change, all of which place a load on the purifiers.
Grinding efficiencies also can be impacted since the temper times or moisture levels might change. It’s important to stay on top of that.
Purifier tune-ups will ensure proper semolina distribution, which is very important.
A key aspect to consider is that the balance of air and product should be maintained consistently in order for the purifiers to separate and grade stock effectively. This balance begins with the feeder gate to the purifier. The stock should feed across the entire width of the sieve, and it must travel evenly down the full length of the sieve.
In addition, staying attuned of seasonal changes, making sure that purifiers are in tip-top shape, changing screens when necessary, and adjusting air valves will help improve overall efficiency.
Bran Finisher Efficiency
Bran finishers play a pivotal role in boosting product yields while maintaining the integrity and quality of the end flour product, such as enhanced appearance, texture refinement, and improved shelf life.
This equipment uses a centrifugal action to gently separate the endosperm attached to the bran, thus reducing flour loss and ensuring higher yields.
In some respects, bran finishers serve as a checkpoint at the end of the breaks whereby if they’re not functioning properly, a small percentage of the stream may end up as millfeed. But those seemingly small percentages can add up quickly to big losses.
Checking over the bran finishers during spring and early summer is a good routine to follow.
Some of the key items to consider include:
• How much high-protein flour is being recovered?
• What do the overs and throughs look like?
• Is any flour and endosperm being left on the bran after the last bran finisher?
• Check starch levels in the laboratory.
• Does any endosperm appear in the shorts’ stream?
• Are the beaters in good condition?
• Are the beaters still sharp or do they need to be turned or replaced, depending on the model being used?
• Are the gaps of the beaters adjusted well?
• Are the screens being changed on a regular basis before they develop holes?
- Karl Ohm, contributing editor
Editor’s note: For further reading, see: “Balancing Damaged Starch,” Fourth Quarter 2021, Milling Journal.