“B” is for Baking Cookies
By Lisa Kobs, M.S.
When creating cookies, developing the right formula in the face of complex ingredient interactions is the first challenge. However, once the formula is set, the processing method can dramatically affect both the cookie’s form and eating quality. In the September 2001 issue of Food Product Design, we addressed ingredient issues in “‘C’ is for Cookie.” This month’s article examines processing for creating quality cookies.
Fixed in the mix
The first step in cookie production is bringing all the ingredients together through mixing. Although gluten development — required for bread and other yeast-raised products — isn’t necessary, mixing serves other critical functions.
Manufacturers employ three primary mixing methods for cookies: single-stage, multiple-stage and continuous process. In single-stage mixing, all of the ingredients except the particulates are added to the mixer at same time. Because mixing is performed in only one step, proper aeration of the formula fat may be difficult to obtain, so this method is not suitable for cookies requiring a high degree of aeration. Obtaining uniform ingredient dispersion also may prove critical — especially with minor ingredients, such as leavening agents. Another concern is lumpiness from water being added to the dry ingredients all at once.
Single-stage mixing can produce a significant rise in dough temperature because of the large quantity of dough in the mixer and longer mix times required for even ingredient incorporation. If dough temperature is critical for a later phase of processing, manufacturers can take some steps to keep it under control. Starting with the right temperature of dough water (as mathematically calculated based on ingredient temperature), mixing times and amount of expected friction can prevent and control heat build-up. Water can be cooled with ice if necessary to obtain the desired end temperature. A jacketed mixing vessel can aid temperature control by circulating cool water around the dough to dissipate some of the built-up heat.
Multistage mixing involves two or more steps. It is the method of choice when ingredient uniformity is very important, air incorporation into the dough is key to the finished product, high levels of sugar need to be incorporated into the dough, or critical ingredients need extra mixing control. Manufacturers use this method most often for cookies with higher fat and sugar contents, such as wire-cut or deposited cookies.
In the first step, known as creaming, fat and sugar are beaten to incorporate air. This is followed by the addition of liquid ingredients. Adding water and other liquids as a second stage allows them to form an emulsion with the fat and sugar. Additional dry ingredients are next, followed by any particulates, such as chips or nuts. When adding delicate inclusions, the mixing time at the final stage should be kept to a minimum to prevent damage. Because mixing variations will be evident in the finished cookies, be sure to determine optimum mixing speeds and times and stick with them as long as the ingredients remain consistent.
Continuous mixing is most effective on a dedicated line where it can maximize throughput and minimize downtime. Speed, efficiency, process consistency, reduced labor requirements and product uniformity all are reasons to select this mixing method.
Both single- and twin-screw extrusion techniques fit the needs of cookie manufacturers. Depending on the screw design, these methods can achieve the varied mixing actions required throughout the dough-forming process. The optimal continuous-design system is flexible at all points in the process so it can be used with many different formulas. As with multistage mixing, mixing times, temperatures and speeds must be optimized carefully in a continuous system.
In addition to mixing style, the type of mixer used and the style of blade affect the outcome. Different types of doughs will react differently just by changing the mixing apparatus or even the mixer size. Blade type, selection, configuration and direction variability, and rotational speed determine mixing actions of cutting and shearing or kneading.
Deposited cookies, wire-cut, rotary-molded and sheeted cookies all have their preferred mixing style to achieve an optimal finished product. “Generally, the same cookie formula will spread less with a creaming mixing method compared to an all-in mixing method,” explains Brian Strouts, head of experimental baking at the American Institute of Baking, Manhattan, KS.
Occasionally a manufacturer will add a rest period, or “floor time,” for the dough after mixing. This can benefit some types of dough as it promotes ingredient hydration, allows the sugar to continue dissolving and gives the leavening reactions a chance to kick in. Floor time also may improve the dough’s handling properties. In some cases, the dough will become cohesive and less sticky so it releases more easily from manufacturing equipment.
Getting in shape
Several types of forming equipment give cookies their shape. The primary types of cookie forming are rotary molding, wire-cutting, depositing and extruding.
Rotary molders make cookies by forcing a dry, almost crumbly dough onto a cylindrical die with cookie designs embossed on its surface. The machine then releases the dough pieces onto a belt. Dough for rotary molding must be very stiff with low water and fat levels to maintain the shape and imprinted image. A less-sticky dough also tends to release more easily from the forming dies. Rotary-molded cookies must bake without changing shape and with little spread or volume increase.
With wire-cut cookie manufacturing, feed rolls carry the dough through a series of openings on a die plate at the bottom of a hopper. A wire moves across the surface of the die plate and cuts the dough stream as the rolls force it through the opening. Wire-cut dough should be cohesive, yet able to withstand the cutting action. It is softer than rotary-molded dough, but can cause problems if it becomes sticky. It must be short enough to be cut cleanly by the wire and deposit accurately. High water and egg levels allow the dough to hold together during cutting. This higher water content means that excessive dough mixing or handling may lead to over-development of gluten and a tough texture in the finished cookie. One trick to promote tenderness is to incorporate the shortening with the flour prior to adding the water.
Deposit cookie dough typically is soft and rich. It can be deposited by pumping or through suction-piston depositing. The pumping method pumps dough at a constant rate from a hopper to the depositing head and deposits it onto the baking surface. How long the depositing valve is open determines the cookie size. With suction-piston action, the depositing piston is retracted, thus forming a partial vacuum. This vacuum pulls the batter into the piston chamber, so when the machine drives the piston forward, it pushes the batter through the depositor’s opening. Dough consistency is the key to producing cookies of similar size and weight. The recent popularity of gourmet-style cookies with very large particulates that can clog depositor heads and cause weight inconsistency presents an even greater manufacturing challenge.
Manufacturers use extrusion-processing techniques to make dough-enrobed cookies, such as fruit-filled bars. By placing one extrusion head inside another, they extrude the dough at the same time a filling is co-extruded into its center. Extruded cookie dough must be extensible and not very sticky to run properly in the extruder.
Sugar wafers are essentially a dehydrated starch gel formed by cooking a thin, aerated batter on a system of heated upper and lower plates. Leavened by the steam that forms from the heat and the pressure of the closed plates, the wafers bake and take on their characteristic textured designs. Often stacked and filled with a cream filling, they have little in common with the other styles of cookies in regard to both formulation and processing.
Formulation criteria include sufficient water content not only to disperse the ingredients, but also to obtain a low-enough viscosity to flow over and cover the plates. Gluten strength is a key to finished-product quality, so proper flour selection becomes very important. Gluten strength should be sufficient to provide body to the wafer without making it too weak and fragile or excessively hard. Leavening agents affect wafer texture by increasing the number of gas cells in the batter. Adding modified food starch also can customize the product texture.
Putting the heat on
Another area where operator manipulation affects the finished product’s success is in the baking process. “Oven types depend upon the volume of product to be produced,” explains Strouts. “However, any type oven will do an adequate job.”
Cookies typically are baked on a band oven, though smaller bakeries may only have the option of rotary ovens, which afford less control. “Direct-fired tunnel ovens are more commonly used for low-moisture cookies, such as rotary cookies, and indirect-fired tunnel ovens are used for soft cookies, such as wire-cut or extruded,” says Strouts.
The trick to achieving the desired finished characteristics is the regulation of various oven zones. During baking, the fat melts, sugar dissolves, leavening agents are further activated, structure is formed, moisture is removed and crust surface color develops. The temperature settings in the oven’s various zones controls or modifies each of these actions. Prescribed changes in the spread ratio, surface appearance, moisture levels, mouthfeel and texture all are in the hands of the savvy baker. The formula and finished product will dictate baking conditions.
“Controlling the humidity in the oven will have an influence on the cookie characteristics,” adds Strouts. “Rich cookies (high in fat and sugar) will be better baked at low temperature and longer time.”
After baking, care needs to be taken in the cookies’ cooling process — which is controlled by manipulating temperature and humidity. If crisp cookies cool too rapidly, they may check or fracture. This forms internal fractures that cannot be seen immediately, but cause breakage during packaging or shipping. Crisp cookies also suffer from a lack of crispness if they are exposed to high humidity levels. Packaging crisp cookies at a temperature slightly higher than ambient helps resist moisture pick-up. Soft cookies are not as sensitive to cooling conditions.
With the finished product in hand, now the trick is to decide whether it’s a gold standard or a reject — not an easy task when hundreds of cookies whiz by every minute. Consistent size is particularly critical for sandwich cookies or those with restrictive packaging. Here is where newer technology can help. In the blink of an eye, an online two- or three-dimensional monitoring system evaluates product size, shape, particulate level and distribution, color and surface appearance. Often featuring built-in statistical capabilities, manufacturing plants can pull up an accurate evaluation of line efficiencies, product counts and rejection levels. Used correctly, these technologies can become an essential part of the development process, especially in the fine-tuning stages of ingredient and process manipulation.
Combining ingredients yields innumerable cookie variations. Varying processing equipment and manufacturing conditions offers a smaller, but still significant, number of cookie variations. By creatively combining both formula and process variations, product designers have a potentially endless array of cookie possibilities.
Lisa Kobs, M.S., is a Minneapolis-based food scientist and technical writer who focuses on new product development.
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