Pretzels are a snack food, which have unique, two looped, knot shape, a hard, brittle or soft, chewy texture and a brown glossy surface color. They are one of the world’s oldest snack foods, first developed during 610 A.D. by a monk in southern France or northern Italy from scrap bread dough. According to popular legend pretzels were given to children as a reward to those who said their prayers correctly and because of that the crossed center of the pretzel form represents the crossed arms of prayer, the early Christian sign of the cross. Today, pretzels are mass produced using primarily automated machinery.
There are two types of pretzel, soft and hard. Soft pretzels are traditionally shaped and consumed as fresh. Hard pretzels are smaller, crispy and could be consumed several months after manufacturing if they are packed in good packaging. Combination of alkaline exterior and acidic interior gives a pretzel unique sensory characteristics.
The pretzel is a simple food. The most common ingredients in hard pretzel manufacturing include wheat flour, water, yeast, leavening agents, shortening, salt and sugar.
Wheat flour is the most important ingredient in pretzel manufacturing. The flour used for pretzels is called soft wheat flour and has a protein content of about 9%. It is the largest component in the dough making up about 65-70% of the total recipe. The manifestation of flour quality on pretzel quality is as a function of its protein content, protein quality and the levels of damaged starch and pentosan.
Shortening used in pretzel manufacturing is a solid form of vegetable fats and oils. It helps the dough stay softer, increases the volume, gives it a crumbly texture, tenderness, moisten mouth feel, improve structure and strength, provide lubricity, incorporate air and aid in the transfer of heat. A pretzel recipe may contain 2-8% vegetable shortening, and it is one of the lowest fat contents among snack foods.
Yeast and chemical leavening agents are used separately or both to provide lighter and crispier final product and improved taste (yeast). Yeast is typically supplied as a dry, granular product. Dry yeast is desirable because it can be stored for a long time at room temperature. Leavening agents have a similar effect as fermenting yeast, however they have less effect on the final taste. Chemical leavening agents may include materials such as sodium bicarbonate and ammonium bicarbonate.
Other ingredients used in pretzels manufacturing are: water, salt, sugar, seasonings, etc. Water makes up about 30-35% of the hard pretzels recipe. Water is important because it lets the dough flow and allows the yeast to contact the sugars for fermentation. It also causes the chemical leavening agents to activate. Salt helps to make the dough stronger in addition to improving the taste. Sugars such as sucrose or corn syrup are often used in the preparation of the pretzel dough. The sugar has the primary effect of providing food for the yeast cells. Additionally, it will give a slightly sweet taste and also contributes to the brown color of the pretzel.
Hard pretzel production process includes dough mixing, forming as shaping using an extruder at low pressures or rotary cutter, cooking in a hot alkali solution and baking.
Dough mixing is a critical step in pretzel production. Pretzel doughs are typically drier based on the water required by the flour for optimal gluten development. The mixing time varies among producers based on the type of mixer, flour properties and operator judgment of the dough property. Since pretzels are made using lower protein flours, they do not require longer mixing times as compared to bread use flours with higher protein content. Furthermore, mixing time is critical since low protein flours have a lower mixing tolerance; i.e., breakdown of gluten due to increased mixing time. The amount of water added and the mixing time are critical for optimal gluten and dough functionality.
When yeast is used in the recipe dough temperature and resting time due to yeast activity and its effect on dough property are also important, as well as mixing room conditions. Warm and humid conditions in the room will promote greater yeast activity thus requiring shorter rest time.
In comparison to continuous mixers, batch mixers have the advantage of being very ﬂexible and able to handle a wide array of formulations and products. Main disadvantage of batch mixers is the change in dough viscosity that occurs during the time interval between batches and creates variations in the weight of the product in extrusion type of dough forming.
Dough forming in many companies is done by extrusion devices in which the dough is forced through an opening and stamped into shape with a wire cutter (Picture 1).
Picture 1. Pretzels dough extrusion
Another way to make a pretzel shape is to use rotary cutting system, after laminating, sheeting/gauging which as in hard biscuit dough or cracker production (Picture 2).
Picture 2. Pretzels dough rotary cutting
Cooking of pretzel dough is done by passing the dough through the hot alkaline solution. Of all the operations in the production of pretzels, cooking is the most important. Most critical parameters for proper pretzel dough cooking are: time, temperature and alkalinity (pH). They are the key factors in developing the taste in pretzels. The alkaline bath is filled with an aqueous solution of either sodium carbonate or lye. The resulting bath has a 1-2 % concentration of sodium hydroxide (NaOH) and a temperature of about 85- 95°C The pretzels are dipped in the bath for 5-20 seconds and typically float when they are finished. This process gelatinizes the starch on the pretzel's surface making it gummy and sticky, allowing the salt to adhere more readily. The gelatinized starch also undergoes Maillard reaction in the oven giving pretzel its shiny brown color on the exterior surface. Any changes in the temperature or strength of the cooking solution will alter the degree of starch gelatinization and consequently pretzel color and texture. After cooking, the wet, steamy pretzels are conveyed under a steady curtain of salt.
Baking and drying are done in most cases in industrial tunnel oven. Baking has several important functions including setting product structure, color, development and moisture removal from the shaped dough. In the past, many bakers used direct-ﬁred ribbon burners installed above and below the oven band. Although generally inefﬁcient, well-designed, direct gas-ﬁred (DGF) ovens have broad capabilities for matching product proﬁles because of the multiplicity of burners and ability to operate each one at a different setting. Today, the most popular ovens used in making pretzels are hybrid designs that combine radiant and convective energy control in the ﬁrst zone and forced convection in succeeding zones and in the drying section. Each pretzel product has a heat process proﬁle adequate to its particular shape and/or formula. For optimal results, the oven must have the capability of matching its heat proﬁle with the requirements of the pretzel type. Final product has 2-4% moisture content, shiny, brown surface, brittle texture and basic, but nice taste.
Cooling and packing are the last phases in pretzels manufacturing. From the ovens, the pretzels are passed along varies conveyors and allowed to cool. As the pretzel cools to room temperature, it becomes more fragile and must be handled with greater care. They are then moved along to the packaging machines, where the pretzels are weighed and the correct amount is placed in the packaging. They can be put in many different types of packages, but it is important that packaging material has adequate barrier characteristics and packaging is tight to prevent the uptake of moisture by the product.
Edmund W. Lusas, Lloyd W. Rooney, 2001. Snack Foods Processing, CRC Press
Ni Yao, 2004. Hard Pretzels Characterization and Process Optimization, A Thesis in Food Science, The Pennsylvania State University, The Graduate School College of Agricultural Sciences
J. H. Shollenbergeb, Marketing Economist, W. K. Marshall, Assistant Marketing Economist, Grain Division Bureau of Agricultural Economics, 1927. Flour for pretzels, Technical bulletin No 46, United States Department of Agriculture, Washington, D.C.