The mysteries of mixing
Mar 1, 2010 12:00 PM, By Ann Juttelstad, Contributing Editor Baking Management Magazine

“Mixing is the most important part of the entire dough making process,” says Noël Haegens, owner of Classo Foods and senior baking technologist, Tate and Lyle, London. The mixing process shears, stretches and kneads the dough to incorporate all the ingredients uniformly. “If the dough is undermixed or overmixed, you will notice it in the handling qualities of the dough,” he says. The mixing of the dough has a number of objectives: to incorporate all the ingredients uniformly, to hydrate the flour and other dry ingredients and to develop the gluten. Gluten development results from a combination of water, flour and energy.

Four types of mixers are commonly used in the baking industry: spiral, planetary, horizontal and oblique mixers. Each mixer offers unique functions.

Spiral
“Spiral mixers, in my opinion, are the most versatile machine available for the bread baker today,” says Michael Eggebrecht, bakery consultant and a representative of WP Bakery Group, Shelton, Conn. Spiral mixers can handle a wide range of dough capacities, with many able to go as low as 15 percent of overall capacity. They also can mix in reverse, which is ideal for adding ingredients at the beginning of the mix, as well as inclusions, such as grains, raisins, nuts or olives, at the end of the mix.

What drives the bowl also should be considered. Some companies offer a gear-driven bowl, while others offer friction wheels to turn the bowl. Friction wheels will wear out over time, while the friction of metal against metal in a gear-driven bowl may eventually affect the motor. Bakers must decide which system is best for their operation.

“The most important thing to look for,” Eggebrecht continues, “is that the spiral mixer itself has very close tolerance between the spiral hook and bowl. Some do not have close enough tolerances, and many times this results in an uneven incorporation of the dry ingredients, and some flour can be left on the bottom of the bowl.”

John Squire, district manager, Kaak Group North America Inc., Lithia Springs, Ga., agrees that spiral mixers are the best for most applications but cautions that not every spiral mixer has the same rotational speed, and those with a small spiral tool may need additional breaker bars to reduce mix time because the spiral will not grab enough dough. Longer mixing time may increase dough temperature, which must be lowered by adding cold water or ice. Additionally, the smaller spiral equipment may torque out as dough stiffens.

Planetary
Planetary mixers are typically used in foodservice or other small bakeries and are not ideal for bread production. “Planetary mixers typically generate more heat in the dough, and they require more scraping to ensure that all flour and dry ingredients are incorporated properly. Most of the time, the mix time needs to be increased compared to a spiral mixer,” Eggebrecht says.

Horizontal
Horizontal mixers also are not recommended for the production of high-quality hearth bread, Eggebrecht says. However, they can be used if that is all a bakery has available. “Great care must be taken to ensure that mix times are adjusted, and the doughs are carefully monitored to achieve the right consistency,” he advises.

Oblique
Oblique mixers or fork mixers are often used in France for producing high-quality hearth bread, although a few U.S. bakeries use them as well. The oblique mixer's actions mimic the motion of human hands. “The main disadvantage of an oblique mixer is that you must fill the mixing bowl to at least 50 or 60 percent of the overall capacity so the mixing action can turn the bowl,” Eggebrecht says. “The bowl is driven off the friction created from the dough against the sides of the bowl, and without a continuous dough ring around the bowl the mixer will not rotate properly. Additionally, mix times are often longer than when using a spiral mixer.” He recommends using an oblique mixer for producing white lean breads, such as French baguettes and ciabatta.

Wendel
One of the newest mixer models is the Wendel, which features twin stirrup-shaped dough hooks designed to offer more complex kneading action. It reduces mix times and offers the possibility of up to four percent more water absorption. The mixer can be used for all dough types, from heavy wheat dough to delicate puff pastry.

The importance of ingredients
Along with the mixing equipment, other critical components of the mixing process are the ingredients themselves

“Different flours or dough recipes can often require the use of different mixers or techniques,” Kaak's Squire says. Different flours also have varying water absorption properties that bakers need to be aware of in order to adjust their formulas and mixing technique properly.

In general, whole wheat flours require shorter mix times to prevent the tearing of the fragile gluten structure. A short autolyse will assist in hydrolyzing the protein and reducing the mix time.

Grains and seeds should be soaked prior to adding to the dough in order to soften them, and the salt should be added to the soak to help prevent enzymatic activity from damaging the dough, Eggebrecht says. Adding the soaker at the end of the mix will help reduce the cutting action of the grains.

Strong flours used in artisan baking may need softening to increase extensibility. This can be done by increasing mix times, adding more water to the dough or by using a liquid enzyme preferment.

Weak flours require bakers to watch mix times very carefully, usually reducing mix times and lowering the hydration of the dough. Ascorbic acid may be added at 15ppm to 30ppm (as a starting point) to increase dough stability.

As the dough is processed, heat increases due to the friction of the dough and the hydration of the flour, which may adversely affect the dough. Cold water or ice water may be added to decrease the temperature of the mixture. Haegens computes friction factor using the following equation:

3xt°Cdough -(t°C room +t°C flour +t°C water) = friction factor

Once the friction factor has been determined, bakers can calculate the amount of ice needed to create the desired dough temperature using this equation:

3xt°Cdough -(t°C room +t°C flour +friction factor) = t°C water

Dough mixing is a complex and sometimes daunting process which, when properly executed, will produce loaves with high quality and shelf stability. Research continues to help bakers determine the precise process by which they can achieve better yields, increase throughput and produce a bread product with excellent flavor.

Science behind good doughScientists at the USDA's Cooperative State Research, Extension, and Education Service (CSREES), have followed particles of wheat dough using a Farinograph mixer through the mixing process to determine the parameters of what makes good quality dough. The researchers found that the “sweet spot” in a mixer is directly between the blades, allowing optimal mixing properties. Further studies are looking at the energy input efficiency when converting flour and water into dough. The study will examine the effect of blade speeds on the dough, the exchange of material during the mixing process, and will compare the Farinograph mixer results with mixers used in commercial applications.

This research will help mixer manufacturers develop even better mixing systems for bakers and may someday provide the formula for the creation of the perfect dough, each and every batch. Until then, bakers have an array of mixing and ingredient experts offering a helping hand.