Predicting performance of flour blends
June 1, 2010
by Bronwyn Elliott
The demand for higher quality and product consistency is increasing in all markets. In some cases, specific flour quality can be used to achieve premiums, while in other cases improved quality is required just to stay ahead of the competitors or to ensure market share.
Blending flour streams gives the miller flexibility to minimize production costs while meeting different customer specifications. Blending flour from different suppliers gives bakers flexibility to receive flour from a range of alternative suppliers, over a range of different specifications, even over a range of different countries.
MEETING SPECIFICATION, MINIMIZING COST
Individual flour streams are produced at various stages of the milling process, each with different composition and characteristics. All mill streams may be combined to produce “straight run” or “straight grade” flour, but more profitable is “split run” or “divide” milling in which flour streams are blended in various combinations to produce different grades of flour for specific customers, processing characteristics, geographical preferences and product uses.
By adjusting the process, or blending different flour varieties and mill streams, a wide variety of specialty flours can be produced. This gives the miller flexibility when selecting wheat to minimize production costs and maximize profits.
Most modern mills have extensive flour storage and blending systems (continuous or batch blend). Mills may produce pre-milled “base” flours for storage and blend to meet the flour specifications of each customer. This provides the maximum flexibility for producing flour grades from a reduced number of wheat grists and longer mill runs. The use of high-cost, premium wheat is minimized and small quantities of specialty flours can be produced at the lowest cost.
TESTING FLOUR STREAM QUALITY
The economics of flour milling are such that it is advantageous to achieve a high yield of flour. Flour commands a premium price over the other components of the wheat grain separated in the milling process, although the extent of this can vary widely. Generally, the more flour produced from a given quantity of wheat, the more money the milling process generates. Thus there is incentive for the miller to include as much bran in flour as possible, while still meeting customers’ specifications.
Regular mill stream analysis, often by continuous in-line near-infrared monitoring, allows the miller to maintain control over milling efficiency and flour divides. Each mill stream is monitored for moisture, ash, protein and possibly color.
However, moisture, ash, protein quantity and color are not the whole story. Dough strength has been synonymous with flour quality, governing the suitability of flour for a specific end use. Strength is associated with wheat or flour protein and encompasses both quantity and quality measurements.
Dough mixing characteristics have been an important part of assessing flour quality for more than 60 years. Most methods are based on assessing the physical properties of the gluten network formed after mixing and their correlation with some end-use baking property. The precise specification for dough mixing parameters will depend on many factors, including the product, process, recipe being used, and the required qualities of the final product.
Standard physical dough test measuring equipment comprises a mixer bowl of specified geometry in which mixer blades or mixer pins rotate. As mixing proceeds, the changing resistance of the dough ingredients is measured as torque on the mixing arms. The measured torque is continuously recorded, the curves indicating the amount of torque, or strength, required to mix the dough to a defined consistency, and the length of time the torque stays steady. This process indicates the resilience of the gluten protein matrix that develops.
However, traditional physical dough tests are only useful in determining the direction of adjustments to the product manufacturing process required when flour changes and cannot be taken as absolutes. An increase in laboratory mixing time does not indicate the exact increase in mixing time required in the commercial process.
Standard tests do not adequately relate to important quality characteristics, are slow, have poor process relevance, are suitable for limited sample types, and produce results that are usually limited to either the mixing or end-use quality of bread flour, ignoring the use of flour to manufacture other products.
Thus it is necessary to develop new specific tests that better predict quality and processing characteristics.
A NEW QUALITY TESTING METHOD
The doughLAB and its small (4 gram) sample-size version, micro-doughLAB, are relatively new instruments to measure the water requirements and dough making properties of wheat flour. The doughLAB incorporates an automated dispenser and variable temperature and speed control systems, providing users with the flexibility to emulate modern high-energy mixers, multi-stage mixing, chilled dough systems and heating of dough.
Emulating commercial high-energy/high-speed mixing conditions.
The doughLAB was designed to emulate the high work rates of modern dough mixers, able to deliver up to 60 kilojoules/kilogram/minute (kJ kg- 1 min- 1 ) when mixing at 150 rpm in its 300-gram mixing bowl, developing a typical pan bread dough in about 2 to 3 minutes. This is similar to the work rate and dough development time for high-speed commercial dough mixing for production of bread and related products such as bagels, soft pretzels and pizza crust.
Emulating chilled mixing conditions.
Modern bakeries employ high energy and low temperatures in the production of raw and pre-cooked frozen dough products. Fitted with a chiller, the doughLAB is capable of test temperatures down to 10 degrees C. This method can be used to mimic production conditions for hard, soft, and whole meal flours and full bread formulations.
Emulating two-stage mixing of formulations with fat.
A two-stage mixing method has been developed to assess high fat formulations used for laminated products such as brioche. In this case, a low-speed mixing (63 rpm) step is used first to blend the ingredients, followed a by high-speed (110 rpm) step to develop the gluten network.
Dough with ingredients and full formulation dough.
Tests have been developed to monitor dosage effects of additives that modify mixing properties, such as dough conditioners, reducing agents, amylases and sugars.
Monitoring commercial dough consistency.
To help avoid dough-handling problems in bakeries, dough can also be taken directly from commercial mixers and its consistency measured in the doughLAB.
Low-water (crumbly) dough for pasta, pastry, cookies, crackers, noodles and wanton wrappers.
Low water (down to 30%) dough may also be tested in the doughLAB. High-speed (180 rpm) mixing is used to test samples for suitability in biscuit (cookie), cracker, noodle, pasta, pastry (pie crust) and wanton wrapper production, mixing at torques around 7.8 nanometers (800 FU), yielding energy input rates around 18 kJ kg- 1 min- 1.
Estimating energy input. The area under the doughLAB graph to the time of the dough development peak indicates the mixing energy requirements of the flour. By knowing this, the baker knows how much energy to add to the flour during mixing and how cold the added water must be to give the correct temperature for proofing after mixing.
REDUCING COST, MAXIMIZING PROFITS
The doughLAB and micro-dough-LAB, with their software package, doughLAB for Windows (DLW), provide flour millers with a tool to assist their blending operations by predicting the functional performance of a flour blend before the blend is made.
The software is capable of mathematically combining data from several doughLAB or micro-doughLAB tests to predict the effect of blending mill streams.
DLW software very closely predicts mixing characteristics of flour blends, showing a very good comparison between actual and virtual curves. Thus the software can be used as a tool for flour blending applications of individual streams with known mixing characteristics, without the need for producing the blend first. Hence blending data is potentially a quicker, easier and more efficient alternative to blending first and then testing flour samples. The modeling tool can also be used to do complex “what if?” analyses without having to run lots of tests.
This feature is especially useful for millers to reduce costs and maximize profits while producing different flour products for specific customers and specific uses.
OPTIMIZE SPECS WHILE MINIMIZING COSTS
Procuring suitable quality flour at the lowest cost is an important goal of the flour buyer, but if the flour causes a problem in processing or end-product quality, the cost-savings may be insignificant compared to the losses later in the chain. A receiving plant, especially if receiving flour from a range of alternative suppliers, over a range of different specifications, even over a range of different countries, may test each incoming flour shipment. On this basis, blends may be designed to maintain specifications for specific purposes and products.
Modeling the performance of blends with DLW software allows their performance to be predicted and offers a powerful tool for managing crop changeover issues.
Being able to predict the functional performance of proposed blends before they are made, using test conditions that model commercial production, enables the lowest cost optimum blend to be identified by both millers and buyers.
Bronwyn Elliott is commercial product manager for Perten Instruments of Australia. She may be contacted at firstname.lastname@example.org.