Pretzel Processing: Perfect Pretzels
December 01, 2009
by Shane Whitaker
Hard or soft, crunchy or chewy, salt or no salt. These are just some of the options consumers encounter when purchasing pretzels. Pretzel manufacturers also have many choices when deciding how to set up their processing lines. Today’s lines can be highly automated and feature more instrumentation, allowing processors to better monitor their systems for a more consistent product.
“A fully automated pretzel line with a continuous mixer could have a single operator overseeing two to three lines, and all this operator would need to do is monitor the lines to make sure everything operates correctly,” said John Eshelman, director, pretzel and snack machinery sales, Reading Bakery Systems (RBS), Robesonia, PA.
Pretzel processing lines include mixing, low-pressure extrusion, proofing, cooking, salting, baking and drying. One of the latest trends is to incorporate components such as extruders, guillotine cutters and cookers on traditional cracker lines to make hybrid pretzel/cracker snacks, according to Mr. Eshelman. “If a cracker manufacturer’s line is sitting idle 20 to 40% of the time, it may look to add an extruder so it can cut shapes or make a stick product,” he said. “If a sheeting line is only running at 70% capacity, what the executive wants to hear is how it can capitalize and get more out of that line.”
A large baking company is incorporated a pretzel cooker on a cracker line to make a hybrid pretzel product. The company uses a proprietary process to cook the pretzel cracker product on one. And he said another major cracker company will likely introduce something similar within the next six months.
MIXING AND CHUNKING.
Pretzels’ heyday was in the 1990s, when low-fat diets were king, and because pretzels are a non-indulgent snack, they were extremely popular. It was about this time that Reading began working with a manufacturer of continuous mixers to sell lines with these systems.
Pretzel dough can either be mixed in batches or with continuous mixers. Because it is traditionally a very stiff dough, horizontal mixers equipped with heavy-duty motors and double sigma-style arms were traditionally used for mixing. However, Reading teamed up with a continuous mixing manufacturer nearly 20 years ago, and today, continuous mixers dominate in regard to what manufacturers of new processing lines are choosing, according to Jim Warren, director of mixing systems, RBS, which purchased ExACT Mixing in 2008, a continuous mixer manufacturing company. “In the past 10 years, I would say that 80% of pretzel lines are sold with a continuous mixer,” he said.
A continuous mixer supplies dough with consistent moisture to the extruder, whereas moisture levels will fluctuate during the 10 to 15 minutes it takes to process a batch of dough from a batch mixer through an extruder, leading to inconsistent products out of the oven, according to Mr. Warren.
RBS manufactures all the processing equipment needed for pretzel lines and can install systems from ingredient handling through finished product conveyors. Taking an older pretzel line and trying to automate it is not the easiest thing to do, according to Mr. Eshelman. However, one of the first things a manufacturer should look at is automating the dough handling system. “That does a couple of things for you,” he said. “First, it reduces your labor requirements on the line. Second, it decreases medical claims for carpel tunnel. Third, using an automated dough handling system works better than a line worker in maintaining proper hopper levels within the extruder, and if you can maintain the same level within the extruder, it produces a more consistent product.”
Automated dough handling systems are available for either continuous or batch mixing. These systems will take a mass of dough from a batch mixer, put it into a chunker and then into a lift conveyor and shuttle system that conveys a predetermined size and weight of dough into the extruder’s hopper.
EXTRUDING AND CUTTING.
RBS’s Low-Pressure (LP) extruders generally operate at between 25 and 100 lb per sq in., according to Mr. Eshelman. “The reason for the wide range is because when there is such a large opening in the die face for product such as pretzel nuggets, rods and Bavarian pretzels, the dough does not require as much pressure to get through the die,” he explained. “However, if you are running a pretzel stick, the face opening value on a die plate is small, so it requires more pressure to achieve an acceptable throughput rate.”
If the dough extruded through these units exceeds 100 psi, it begins to damage or crystallize the dough. This can result in a very hard bite and fragile product. “It is starch and/or protein damage that occurs, mainly because of pressure and because of shear,” he added. “If you work the dough too hard, it loses its physical characteristics.”
Reading has machined thousands of different die shapes over the years for pretzel manufacturers, offering standard shapes as well as customized dies. RBS recently introduced its Series 7 high-speed band cutter that clips the extruded dough off the die sheet. This new band cutter features a servo drive system, allowing it to make more cuts than ever before, up to 275 per minute. Also, the servo drive allows the cutter mechanism to stop at the same place every time for greater piece weight accuracy, particularly when cutting larger extruded dough shapes, according to Mr. Eshelman.
PROOFING AND COOKING.
After extrusion, the formed dough pieces convey along a proofing belt, typically made of cotton or a cotton/poly blend that absorbs moisture from the underside of the product, as well as provides product release from the belt. Proof times range from a few minutes up to an hour, depending on the type of pretzel being made. Thicker products like nuggets, rods or thick sourdough pretzels will require longer proofing times. Climate-controlled proofers are important so that the temperature and humidity is the same year-round.
Pretzels pass through an alkaline solution before baking, and the pretzel cooker is perhaps the most underestimated yet important part of the process as it imparts important taste-critical qualities to the product. The cooker features either a bath or waterfall that normally includes a sodium hydroxide and water solution, and the heat and caustic solution that gelatinizes the outer shell of the dough piece, limiting moisture loss and allowing the dough to puff slightly during baking for a lighter texture.
To remove the buildup of solids at the bottom of a cooker tank, RBS recently started putting automatic purge drains in its cookers. The bottom of the tank is sloped and it uses a sump and an automatic valve that opens for a predetermined amount of time every so often to pull the sediment out the bottom of the cooker.
Also, instrumentation is available to constantly measure and maintain the proper solution strength. To provide the greatest flexibility to manufacturers, RBS’s cookers can be baths, waterfalls or both. Some products such as thin pretzel crisps will be dislodged from the belt if submerged in a cooker; therefore, processors of these products will use a waterfall system in which the solution is recirculated through the cooker. If a pretzel manufacturer wants to add new products that would require a waterfall as opposed to a cooking bath, that option can be added at a later time, according to Mr. Eshelman. SALTING AND BAKING. After going through the cooking bath, the gelatinized dough piece travels under a salter before entering the oven. The salt sticks to the crust because it is sticky from the cooker. Because manufacturers must stay within the percentages for sodium listed on nutrition labels, topping accuracy has become critical. As such, Reading now offers Omega pocketed roll dispensers that feature variablespeed drives to precisely apply of salt and toppings such as sesame seeds.
Axis Automation, Waterloo, WI, also offers salters with rotating shafts and fluted ovals machined across the shaft to actively pull the topping from the hopper. Operators can change the amount being dispensed by changing the rpms of the dispensing shaft, using the variable-frequency drive, according to Norman Searle, c.o.o., Axis.
After salting, the dough piece passes through the oven where the primary baking occurs. Most pretzel are baked in tunnel ovens that can be as long as 150 ft. Pretzel ovens operate at extremely high temperatures, and it’s not unusual for them to have temperatures in the range of 650 to 675°F. These ovens generally contain several baking zones, and each zone can be customized to a specific baking temperature, air velocity and exhaust. These ovens feature three basic forms of heat transfer — radiant, convective and conductive — to give the operator additional baking flexibility.
Reading’s ovens typically start with a “Smart Zone” that uses all three heat transfer aspects, according to Mr. Eshelman. Gas-fired radiant tube burners omit a high radiant component to the product, and a penthouse on top of the oven produces hot air that circulates through the oven at different volumes from the upper and lower air supply plenums. Manufacturers can change the proportion of radiant and convection heating, as certain products need a lot of radiant energy but not as much convection air. It they apply too much air, it will skin the product over prematurely, and that makes it more difficult to get moisture out of the product’s core, which could cause it to split open, he explained.
When the product has finished baking in the oven, the final color and shape of the product has been developed, and the last processing step is drying. When a pretzel reaches the end of the oven, its moisture levels will typically still be in the 8 to 10% range, and the purpose of the dryer is to get that down to between 2 and 3%. RBS features a dryer that runs the length of the oven using a conveyor system below the main oven com- partment. While temperatures are less in the dryer than in the oven, there is greater air movement, and dwell times can be more than twice as long as those in the oven.
QUALITY AND CONTROL.
Bakeries also should look to modernize their quality assurance programs because new instrumentation is available such as near-infrared vs. moisture determination balances for measuring moisture of pretzels, according to Mr. Eshelman. And while it may look like it costs a lot to initially invest in these tools, when taken over the long run, it is a good investment, he said. In fact, some pretzel manufacturers are putting near-infrared sensors on lines to constantly measure moisture levels in products.
Many pretzels lines use PLCs and/or PC-based control systems. However, PC-based systems are more comprehensive and offer storage and memory capabilities that are not available with PLCs or touch-screen interfaces, according to Mr. Eshelman. Anything that is being electronically operated or monitored can be trended and saved by PC-based systems, so a company can save data such as extrusion pressure, caustic percentage of cooking solution and oven/ dryer temperatures at any particular time. “Manufacturers will have remote access to the process PC, so they can look at lines from remote locations,” he said. “A couple of larger companies save all data for up to six months, and if brand X sees an inordinate number of returns because it is too salty, burned or stale and the manufacturer has a UPC code, it goes back and reviews what operator and processing parameters were used at the time the product was made.”
Pretzel processing equipment continues to evolve and today systems feature more automation and greater controls to assist processors in making a wide variety of consistent quality products.