Pretzel Processing: With a Twist
May 1, 2010
by Shane Whitaker
What makes a pretzel a pretzel? Is it the knotted shape with three holes that many recognize as the traditional pretzel? Not necessarily, because pretzels today are made in many shapes and dimensions. Pretzels are known for their shiny exterior surface and white interior, yet they can be either crunchy or soft bread-like snacks.
In the past several years, new pretzel products have been introduced to the marketplace such as thin pretzel crisps and crackers that feature a pretzel-like texture on one side and a cracker on the flipside. Whatever the shape, pretzel products are much in demand, according to Harald Bechmann, content manager and senior technical editor, marketing department, Franz Haas Waffel- und Keksanlagen-Industrie GmbH, Leobendorf, Austria. Pretzel production in the US is more than 260,000 tons per year, he said.
While a variety of industrial processes produce pretzels, the following are steps bakers generally follow: mixing, forming, proofing, cooking, salting, baking and drying.
“Making a quality pretzel is an easy thing; making a quality pretzel consistently is a whole different story,” said John Eshelman, director, pretzel and snack machinery sales, Reading Bakery Systems (RBS), Robesonia, PA, quoting an old maxim that Terry Groff, chairman of RBS, has said for years.
Industrial bakeries must be able to make the same product day after day, and today’s highly automated processing lines help them achieve that consistency.
Both batch and continuous mixers are used in pretzel production, and because pretzel dough is normally very stiff, bakers traditionally opt for horizontal mixers equipped with heavy duty motors and double sigma-style arms.
Depending on the technological features of the end product, it is favorable to use either a double-shaft or a double-Z kneader such as DW and LTZ, offered by Franz Haas, according to Mr. Bechmann. “The right kneader has to be chosen considering the required resting time of the dough as well as the capacity of the baking oven and the baking time, both of which ultimately influence the output of the production line,” he said.
As a rule of thumb, Mr. Bechmann explained the mixer should be operated at a minimum of half of its capacity; otherwise, the resting time might be too long.
RBS investigated and identified certain process variables that were directly responsible for influencing the quality of finished pretzel products. “The single greatest variable identified was the textural difference of the dough from the time of exiting the batch mixer until the time of forming,” Mr. Eshelman said. “With active yeast being the main leavening agent in a pretzel formula, carbon dioxide is being generated almost immediately after the mixing process. In the case of a three batch per hour mixing cycle, the generation of carbon dioxide definitely changes the density of the dough during this relatively short period of time.
During the extrusion process, piece weight differences are certainly recognizable with the newer, higher density dough versus the older, lower density dough resulting in variable moisture levels after the baking and drying process.”
Nearly 20 years ago, RBS teamed up with ExACT Mixing Systems and began implementing continuous dough mixers on RBS-supplied pretzel lines. “The results were pretty amazing” said Eshelman. “With all of the dough being the same age and density, the weight variability out of the extruder literally disappeared resulting in a far more consistent finished product.” Today, the company estimates that more than half of new pretzel lines installed in the US are now sold with continuous mixers replacing traditional batch mixing systems.
Since acquiring ExACT two years ago, RBS continued to improved the mixing systems. “One of our more notable improvements is the introduction of the new clamshell mixing barrel design,” Mr. Eshelman said. “The clamshell was designed so processors can more easily access the inside of the mixing barrel for sanitation and maintenance purposes. Once the centrifugally cast barrel is manufactured, we cut it in half horizontally. We then hinge one side and incorporate a motorized actuator on the barrel allowing the operator to open the clamshell door and have complete access to the interior portion of the mixer. The clam shell design also requires less water during sanitation procedures.”
Another area improvement in continuous mixing includes improved accuracy of the electronic ingredient metering equipment. “Mass flow metering for liquid ingredients and loss in weight metering for dry ingredients has improved dramatically over the last several years,” Mr. Eshelman observed. “At one-tenth of one percent accuracy levels, these feeders are now more accurate in scaling ingredients than that of its human counterparts.”
The heart of a pretzel line is the forming and cutting process, according to Mr. Bechmann. Franz Haas offers three different options for forming pretzel products. Processors can make pretzels by extrusion and by moulding as it is used for manufacturing of soft cookies. A cutting line where the dough is laminated into a dough sheet and a cutting machine forms the end product also can be used, he observed.
“The choice of one of these three production methods has to be based on product texture, necessary capacity, product quality of the pretzel and also the desired flexibility of the production line,” Mr. Bechmann said. “For example, it would also be possible to install a combined production line for crackers and pretzels. But this, of course, would entail compromises in product quality or throughput. The advantage of using extruders or moulding machines instead of a cutting machine is that they need much less space than a cutting line.”
Because dough with the lowest amount of water can be made on cutting lines, Mr. Bechmann claimed it makes the highest quality pretzel products. Franz Haas’ Duocut twin-roller cutting machine offers two different cutting methods for pretzels by using either twin-or single-roller mode. “In twin-roller mode, the inner contours of the pretzel are cut by the first roller,” he explained. “The perforated dough sheet is led over a gap. The inner dough pieces fall through the frame onto a cross conveyor and are fed to the dough return transport system. The cutting web carrying the dough sheet is pressed against second roller by a rubber roller. The outer contours of the pretzel are cut by this second roller, and the dough blanks are conveyed downstream.”
In a single-roller mode, the two cutting processes are made in one pass by the second roller. The 1-roller option is easier to work because it is necessary to synchronize the two rollers in the other system to achieve exact product shape, Mr. Bechmann added.
RBS allows processors to form a wide variety of pretzel shapes using low-pressure extrusion and die plates. The company has machined thousands of different die shapes for pretzel manufacturers, offering standard shapes as well as customized dies.
Knowing that newer technology existed, RBS recently invested in a wire EDM (electrical discharge machining) machine to supplement the traditional machining process used for many years. The first step of the process involves submerging the blank die plate in a tank filled with dielectric nonconductive solution. A very small wire with voltage present is then fed to meet the die where the thermal removal process of the steel begins. “Wire EDM will allow us to make far more intricate shapes,” Mr. Eshelman said. “It will also allow us to reduce the end cost to users because once you set up this type of machine, it becomes a ‘lights out’ operation. In other words, once the EDM machining process begins, the machine operator is free to move on to other tasks until the piece has been completed.”
One area pretzel bakers can automate and thus reduce the need for line workers is in twisting operations for soft pretzels. One of the more unusual pieces of equipment for manufacturing pretzels is the MultiTwist — the only industrial robotic twister on the market for pretzels, according to Ken Schwenger, sales manager, Americas, Fritsch USA, Cedar Grove, NJ. Using the MultiTwist, a processor could set up lines making as many as 50,000 soft pretzels an hour with only one operator.
Fritsch introduced the MultiTwist a little more than a decade ago, and the machine is currently in its third generation. The latest version features servo motors compared with earlier designs that were pneumatically driven, according to Dieter Wolf, marketing director, Fritsch GmbH, Markt Einersheim, Germany. The servo-driven MultiTwist is extremely quiet, reliable and precise, he said.
Fritsch builds complete pretzel lines from bulk ingredient delivery through cooling, but the MultiTwist is the heart of its lines, according to Mr. Wolf. The MultiTwist can be fed with dough strands from either divider/rounders or sheeting lines, and it can handle dough pieces ranging between 30 and 250 g, making up to 2,000 pieces per hour on a single unit. A single dividing or sheeting line can feed up to eight MultiTwist units for producing as many as 16,000 pretzels per hour.
A dough divider with intermediate proofer is the most popular system because it is less expensive and doesn’t produce scrap dough, according to Josef Hoos, senior manager, technical and projects, Fritsch GmbH. However, the advantage of a sheeting line is that it doesn’t have to be cleaned as often. Whereas dough dividers have to be cleaned every 12 hours, with sheeting lines, a processor can run three shifts five days a week without stopping, he explained.
The MultiTwist also features intelligent tool control, which means it always checks to make sure the right tools are installed on the machine and all the settings are correct. There are always two parts to change, and if only one part has been changed, then the machine will not operate.
It only takes a couple of minutes to change the twisting tools, and it is making the lines extremely flexible in terms of weight and sizes of the pretzels and products it can make. MultiTwist can be programmed with up to 25 different products from traditional ring-shaped products to sticks to sweet dough products to traditional soft pretzels that are fed into a caustic bath.
The pretzel’s characteristic crispy bite, white inside and a shiny outside is achieved through the application of a 0.5% solution of food-grade sodium or calcium hydroxide, according to Mr. Bechmann. After shaping, pretzel products are generally fed into the caustic bath. “Depending on the dough, the end product, the recipe and the production speed, the manufacturer can choose from different types of baths with cold, warm or hot solutions,” Mr. Bechmann said. “Furthermore, the products can be submerged completely in the bath or just sprayed with a caustic solution, or can also be processed with a combination of both. Excess caustic solution is blown off to keep baking times short and energy use efficient.”
RBS’s newest pretzel cookers offer multiple cooking functions, including the traditional bath where the entire pretzel is submerged in the solution. However, the cookers also offer a waterfall feature that showers the solution over the top of pretzels. “A really thin pretzel product will have a tendency to disintegrate into a gelatinized mass if submerged in the solution,” Mr. Eshelman said.
The waterfall also is advantageous for proofed products, because this type of dough has had time to generate higher levels of carbon dioxide and become buoyant. “If you try to submerge these products, they will dislodge from the cooker conveyor belt and float to the surface resulting in disorientation once they are finally transferred to the oven belt, and you simply can’t have that happen,” he said.
Pretzel processors have expressed more interest lately in electrically heated vs. gas-fired caustic cookers according to Mr. Eshelman. “The reason for this is the simplicity of electric cookers, and the fact that electric heating the solution is 100% efficient, whereas gas-fired methods are about 90% efficient. Depending on a bakery’s electrical rates, electric cookers could be a cost effective option and are less complicated and easier to maintain.”
RBS’s Spectrum oven, which is widely used for baking pretzels, underwent several design changes over the past several years. “The greatest improvement is using far greater amounts of insulation than to that of our older systems,” Mr. Eshelman said. “We have added 4 to 6 in. of additional insulation throughout the structure of our tunnel ovens. These changes were made to help enhance energy conservation.”
And to that end, the company has also redesigned access doors and door seals to minimize heat loss. A pretzel oven generally offers a generous number of access and cleanout doors because the oven is prone to salt accumulation. “You have to be able to get into the oven to clean it out,” he said.
RBS also introduced insulated returns for the belt traveling back in the drying chamber, minimizing heat loss and energy wasted to reheat the belt when it re-enters the oven chamber. When the oven belting is exposed to ambient room air temperature, it loses heat very rapidly, so when it goes back into the oven, it has to be heated up quickly. “With fuel conservation being a high priority for most bakeries, we have found that reheating of the oven belting may consume up to 30% of the energy requirement to bake the product,” Mr. Eshelman said.
For baking pretzels, it is important to strictly follow a certain baking zone pattern and heating profile, and the number of zones included in the process depends on the oven length, according to Mr. Bechmann. “The longer the oven and the more zones can be integrated, the better the optimal temperature curve can be regulated, and the better the product will be,” he said.
The first zones are usually directly fired and longer than the zones further downstream because a high energy input is required to adequately and evenly bake the product. The final baking zones function as dryers with the main purpose to give the product the optimum color.
Choosing the proper oven band is also a decisive factor for good results. “Usually, light wire-mesh bands are adopted,” Mr. Bechmann said. “If, however, laminated crackers are to be produced on the same line, a heavier wire-mesh band would be necessary.”
To help ensure that pretzels are within a moisture specification, Mr. Eshelman said more plants are using near infrared (NIR) moisture monitoring instrumentation situated at the end of the oven. “The NIR sensor measures moisture content of the product as it exits at the end of the oven. This data is then communicated via Ethernet connection to the PLC which provides the line operator and quality assurance personnel with a real time moisture monitoring capabilities.”
Another trend in the industry is the use of video equipment at the end of the oven. “As plants continue to automate for the purpose of reducing overall labor costs, you simply don’t have as many eyes monitoring finished product quality anymore,” Mr. Eshelman explained. “It’s not unusual to walk into a QA lab these days and see QA personnel viewing a monitor while conducting their routine quality assurance testing.”