Mixograph & Mixolab

What is the Mixograph?

The mixograph is a dough testing equipment used to assess the baking quality of flours from soft, hard and durum wheat. It provides information on the mixing and absorption characteristics of flour.

The mixograph helps millers, bakers and plant breeders to:

? Classify wheats according to baking strength and define their end use or application

? Optimize flour blends and streams at the mill

? Detect proteolytic activity (sprout damage) in wheat

? Evaluate the conformity of incoming flour at the bakery

? Adjust mixing time and water absorption

? Perform genetic improvement of wheat cultivars

? Study the effect of ingredients and dough conditioners on dough mixing properties

? Match quality of flour with type of bakery product

How does it work?

The mixograph is a recording dough pin mixer that rapidly develops a dough sample. It measures and records resistance of a dough to mixing. It consists of small dough mixer constructed in such a manner that the force required (torque) to turn a head over a static bowl containing dough is measured and recorded as a graphical curve called mixogram.

As the gluten-forming proteins hydrate and coalesce, they form gluten strands which bind together to form an elastic matrix. During measurement, the force increases to a maximum and then decreases as the dough is overmixed.

Two different sizes of mixographs are commercially available: 10 g and 35 g. The machine can be hooked up to a computer running a software program to provide detailed and accurate mixing data.

According to AACC International Official Method 54–40.02 (Cereals & Grains Association), the mixograph test consists of the following steps:-

? Check the speed of the mixing head and the swinging arm.

? Adjust the range and settings of the instrument according to official method.

? Place ink in the pen and adjust mixograph paper so the test starts at zero point.

? Flour moisture and protein content should be determined prior to the test. Moisture is critical for sample weight while protein content affects water absorption.

? Keep flour sample in a sealed container to avoid moisture exchange.

? Before test, bring flour, water and bowl to room temperature (tempering to around 25°C).

? Weigh flour sample (35 g) on a 14% moisture basis (MB). Correction of flour weight should be made according to dry solids content.

? Place flour in the tempered mixing bowl.

? Calculate the desired water absorption according to the protein content. The following equation can be used:

A different absorption can be determined by comparing curve characteristics with other mixograms having an “optimum” absorption.

? Fill burette with tempered water. Deliver the predetermined amount of water to the mixing bowl.

? Place mixing bowl containing flour sample and water. Lower mixing head.

? Graph paper and pen should be set and ready in position.

? Turn on equipment and allow to mix for 8 minutes.

? Turn off mixing head. Immediately check and register dough temperature.

? Determine dough properties (height of curve, angle and curve thickness before and after peak and optimum dough development time)

Parameters assessed by Mixograph:

? Water absorption: The amount of water added affects the position and pattern of the curve on the graph paper. Less water increases dough consistency (torque) and moves the curve upward.

? Optimum development time (peak time): Time (min or sec) from the origin to reach the highest point on the center curve. At the peak, the dough has maximum consistency and optimum gas retention capacity. The intersection of lines drawn down the center of the ascending and descending parts of the curve is the peak time.

? Mixing tolerance (to overmixing): Directly related to the quantity and strength of gluten-forming proteins. The width of the mixogram and the angle of descent indicate the tolerance of the dough to overmixing. The wider the curve, the stronger the flour, and the more elastic and less extensible the dough will be. The steeper or the more pronounced the angle after peak, the less mixing tolerance.

As a general rule, the higher the protein content and the stronger the interaction of gluten-forming proteins, the longer the development time, the higher the peak, and the greater the mixing tolerance of flour.

What is a Mixolab?

The mixolab is dough testing equipment used to assess the baking quality and performance of hydrated cereal flours. It’s used to characterize the rheological behavior and pasting properties of flour/water doughs and starch/water mixtures when subjected to the simultaneous action of mixing and heat transfer (changes in temperature).

The mixograph helps millers and bakers to:

? Adjust dough mixing parameters

? Detect excessive enzymatic activity in wheat due sprout damage

? Evaluate starch damage

? Adjust flour’s alpha amylase activity

? Predict product behavior during thermal processing

? Assess the cold/hot functionality of starches and gums

? Study the effect of dough conditioners on dough mixing properties

How does it work?

The mixolab is a recording dough mixer with heating and cooling capabilities. It uses two mixing blades that rotate in opposite directions. The instrument can measure the consistency of dough in the temperature range of 86–194°F (30–90°C) during heating at a rate of 7.2°F/min (4°C/min).

Evaluation of dough consistency over this temperature range allows the mixolab to determine complete characterization of the gluten-forming proteins and starch functionality in a single assay. These functions can be performed by measuring, in real time, sample resistance to mixing action of the kneading arms (i.e. torque in N·m), recorded by a computer software in a graph as changes in viscosity with time.

Application

According to AACC International Official Method 54–60.01 (Cereals & Grains Association), the mixolab test consists of the following steps:

? Flour moisture should be determined prior to the test. Instrument will automatically adjust flour weight according to the moisture value on a 14% moisture basis.

? Input the test conditions (i.e. flour moisture content and desired water absorption).

? Weigh 45 g of test flour and place it into the mixolab mixer.

? Position the water injector.

? Conduct a preliminary test to determine if the selected water absorption is adequate for the run.

? Start the test and verify that during the first 5 minutes, the torque measured by sensor is within 1.10 N·m (C1 point in curve). If in range, allow test to continue. If not, stop the test and repeat procedure with an adjusted new water absorption.

? Allow instrument to continue and complete the test.

? Evaluate the 5 different phases of the mixolab curve or graph:-

o Phase I (initial mixing, hold at 86°F or 30°C for 8 minutes). Evaluation of dough formation and weakening. The most important parameters are maximum consistency (C1 point in curve), time to maximum consistency, and dough stability (measured as the time in minutes in which torque is higher than maximum consistency).

o Phase II (weakening, heating from 86 to 140°F, 30–60°C). Evaluation of gluten weakening as a function of torque reduction, i.e. decrease in dough consistency (C2 point in curve). The 2 most relevant parameters are minimum consistency and dough temperature at minimum consistency. C2 represents the lowest point of the curve.

o Phase III (gelatinization, heating from 140–194°F, 60–90°C). Evaluation of starch gelatinization properties. The 2 most relevant parameters are minimum consistency (C3 point in curve) and dough temperature at minimum consistency. C3 indicates the maximum torque obtained after C2 during the heating phase. It corresponds to starch gelatinization measurement.

o Phase IV (stability during baking, hold at 194°F, 90°C). The most important parameters are gel stability minimum consistency during baking (difference between minimum consistency of phase III at point C3 and IV phase at point C4) and dough temperature at minimum consistency.

o Phase V (retrogradation, cooling from 194 to 140°F, 90–60°C). Evaluation of starch retrogradation. The most important parameter is the increase in torque between minimum consistency of phase IV and maximum consistency of phase V (C5 point in curve). Retrogradation is correlated to bread staling.

? Obtain the mixolab flour profiler graph and relate the 6 factors (mixing, absorption, retrogradation, viscosity, amylase, and gluten) to a reference or control flour.

Analysis protocol of the mixolab is completely customizable (i.e., mixing speed, temperature, water absorption). This allows for maximum flexibility and adaptability to user needs.