Adding to the customary new crop challenges this year are quality and availability concerns surrounding several traditional export countries due to weather and political conflicts. Regardless of the reasons, the fact remains that changing the wheat blend, or grist, of a mill requires thought and planning. As the 2014 harvest in the northern hemisphere is ending, it is the right time to review some fundamental practices used to evaluate milling performance.
Changing the Grist
Consistency and cost are the two primary concerns when making blending decisions during the new crop transition. Both the miller and the baker have reasons to value a consistent product. Delivering a uniform wheat grist to the mill is critical to maximizing flour extraction, while minimizing variation in flour quality characteristics.
Variations in the moisture, kernel size and density of wheat delivered to the mill will negatively affect mill balance and result in lower extraction rates and lower flour output. For the baker, if the wheat is not consistent in protein content and other functional quality characteristics going into the milling process, then the flour will most likely not be consistent in the quality characteristics desired to optimize their process. Delivering a homogeneous mix of wheat to the mill is critical in delivering flour with reliable quality characteristics.
For millers that procure their wheat locally from the same regions each year, a standard practice is to begin blending the new crop into the grist immediately as they begin to receive it at the mill, beginning with a small portion, 5% to 10%, depending on blending capabilities and current inventory levels, then progressively increasing the percentage each week until the old crop inventory is depleted.
The practice allows maximum aging of the new crop wheat with existing storage and logistical restrictions. While this allows the miller to stretch out the time until he has to commit to using 100% new crop wheat on his mill, it does have drawbacks for the baker who has to adjust to changing flour functionality each week as the percentage of new crop wheat increases.
During the harvest season, there can be tremendous variability in the price of wheat. Poor harvest conditions or lower than expected production can push the price of wheat up and cause anxiety over the availability of quality wheat, while ideal harvest conditions and higher than expected production can bring the cost of wheat lower.
These fluctuations in cost impact the blending decisions of the miller and how quickly the inventory of old crop wheat is depleted. Considering both the price and consistency of quality characteristics to the end-user of the flour makes determining the correct balance of old crop versus new crop in the mill grist a challenging task for the miller.
Changes in Kernel Size and Impurities
Changing the types of wheat used in the blend may change the functional properties of the flour, but the first place to evaluate changes in the milling characteristics of a new grist is in the cleaning house. Wheat from different origins, whether that is different countries or different regions within a country, will potentially have different impurities that must be removed prior to milling. In a year such as this year, it is important to evaluate the type and level of impurities that may be present if the country or region of the source of wheat changes.
Changes in the type of impurities may be as simple as the seeds of weeds common to the growing area or other grains in the region that are potentially mixed during harvest, storage or transport. The changes could be more challenging such as unexpected diseases impacting wheat quality such as ergot or fusarium. Close monitoring and adjusting of the cleaning process is required to address these potential changes in the new wheat crop.
Several factors impact the average kernel size of wheat. Class, variety, growing conditions, country of origin and hardness are just a few to consider. These are reasons that miller should consider kernel diameter and thousand-kernel weight, in addition to test weight or hectoliter mass when evaluating the milling quality of wheat from different origins and classes.
Changes in kernel size and hardness will impact the millability of the wheat. Again, awareness in the cleaning system is important as changes in the kernel size may result in loss of quality wheat during the cleaning process if screen size of the cleaning equipment is not adjusted appropriately. Adjusting of scourers, peelers and other equipment that use the principle of abrasion to clean or remove the outer bran layers of the wheat kernel will also require adjustment as kernel size and hardness changes.
Another adjustment, related to kernel size and hardness, the miller will need to evaluate is setting the optimal break release schedule for the mill. Each break roll or passage in the milling diagram has a target release based on the capacity of the equipment feeding and being fed by that roll passage. Changes in the optimal break release schedule can be the result of several variables including the type of wheat, kernel size, hardness and moisture.
All of these variables will change with the new crop wheat or a change in wheat origin. Evaluating the impact on the break system extends beyond simply setting the break release. A full evaluation of the complete granulation profile of each of the primary break passage is recommended. Optimizing the break release means adjusting the grinding of the primary break passages to maximize and balance the sizings production from the break system to the rest of the milling system providing the best operating balance of the mill.
In preparation for the new crop transition, replace worn break rolls. Sharp, well-maintained corrugated or fluted rolls in break passages are important to effectively evaluate the necessary changes during the new crop transition and to maximize endosperm extraction in the break system. A significant change in kernel size or shape due to a change in wheat origin or new crop may require a change in the fluting profiles or corrugations used in the break passages. A smaller, harder wheat kernel will required a slightly smaller corrugation to optimally open and separate the bran from the endosperm.
Sifters and Purifiers
The final aspect of the milling process that must be evaluated during the new crop transition is the sifting or bolting of the new crop wheat. Differences in the hardness of newly harvested wheat as compared to wheat which has aged for a year will increase the difficulty in the bolting of fine stock and flour break and reduction passage.
The bolting performance during the new crop wheat transition requires continual observation as the wheat continues to change during the post-harvest maturing period or “sweat.” New crop wheat tends to require more sifter surface during this sweating period, similar to how softer wheat does not bolt or sift as efficiently as harder wheat. During this sweating period of 30 to 60 days, millers may find it necessary to slightly increase the micron size or “open up” the head end flour sieve clothing of the mill and even reduce the operating capacity of a milling for the first few weeks after harvest. Increasing the micron size of the fine semolina separations in the head end break passages helps to improve the distribution of fine material to the reduction and sizing passages of the mill.
Changes in protein content and functional quality characteristics are other challenges the miller and baker must face together with each new harvest. A difference in protein content does not necessarily equate to a change in the functional characteristics associated with the change in protein content. Early evaluation of the mixing tolerance, water absorption, falling number and other vital flour functionality characteristics enables the miller to advise the baker of the potential changes in flour performance.
Each year, the new wheat crop brings different challenges and opportunities for flour millers and bakers to meet the needs of their customers. Early testing and good communication of the expected changes in milling and baking quality characteristics help to better manage this change.
Changes in the physical properties of the wheat may cause a reduction of the running capacity of a milling for the first few weeks after harvest, but making adjustments to the mill will help to optimize mill capacity and efficiency during this time of transition. The early investment of time and resources to completing a thorough evaluation of the changes in wheat quality characteristics allows the miller to maintain maximum flour extraction and profitability for the company in the long term.
Mark Fowler is associate director of the International Grains Program at Kansas State University. He may be reached at firstname.lastname@example.org.