Dough testing for pasta quality
February 1, 2010
by Bronwyn Elliott
For generations, pasta has been a part of family traditions with the first definitive information about pasta products in Italy dating from the 13th or 14th century. As pasta was introduced elsewhere in the world, it became incorporated into a number of local cuisines. There are now approximately 600 different shapes of pasta enjoyed around the world.
Global pasta markets are growing, driven by the convenience needs of busy consumers and health and well-being issues despite the nutritional concerns associated with pasta, such as high dietary carbohydrates.
Semolina from durum wheat is preferred for the production of pasta products, and the durum grain trade reflects growth in the pasta segment. World production of durum wheat is around 40 million tonnes. The hardness, characteristics of its gluten protein matrix and the dispersion of pigments in the endosperm make durum semolina ideal for producing high-quality pasta with a desirable yellow color and durability for packing and shipping. When cooked, high quality pasta is cohesive, resists overcooking, and the cooking water is non-starchy.
NEED TO MEASURE QUALITY
Most of the durum grown today is amber durum, with grains that are amber-colored and larger than those of other types of wheat. Durum wheat’s density, high-protein content and gluten strength make it ideal wheat for premium pasta products. It is also used for producing couscous and durum breads, particularly in the Middle East and North Africa.
The concept of durum wheat quality is complex. Durum wheat quality criteria continually evolve in response to technological advances in durum wheat milling and secondary processing, market pressure and consumer preference. Globalization and increasing competition in the pasta industry make it more important that processors produce pasta products with quality that is consistent over time. Customers are becoming more discriminating in their quality requirements, and variability in product quality is becoming less acceptable, particularly for premium products.
Increasing demand for specific durum wheat quality attributes for different end-products requires development of more rapid objective means to classify durum on the basis of processing potential. End users of durum semolina would benefit from ways to classify semolina that are relevant to the processes they will use and the products they will manufacture.
Important quality differences include semolina milling potential, protein content, semolina and pasta color, gluten strength and pasta cooking quality and brightness. Grain protein concentration and gluten strength are important for premium pasta with better nutritive value and superior end-use quality, although quality factors such as protein content and gluten strength have different priorities in various durum wheat markets.
IMPORTANCE OF PROTEIN
Protein content is a fundamental requirement to ensure good pasta cooking quality. Protein concentration alone can account for 30% to 40% of the variability in pasta-cooking quality. Durum cultivars with high protein produce macaroni, spaghetti and other pasta products with greater cooking firmness and increased tolerance to overcooking. Near-infrared spectroscopy to measure protein content is a rapid, objective durum wheat quality classification tool and has become widely accepted. High temperature and ultra-high temperature drying have become the processes of choice for most pasta manufacturers due to their ability to compensate for variability in raw materials. However, gluten quality, not only protein concentration, is likely to remain an important specification.
Physical dough tests are also important because they determine the behavior of dough during mechanical handling which affects the quality of the finished pasta. Many millers and pasta manufacturers will evaluate gluten quality through tests such as wet gluten content and physical dough development tests.
STANDARD METHODS FOR PHYSICAL DOUGH TESTING
Physical dough test instruments mix semolina and water in measuring equipment that comprises a mixer bowl of specified geometry in which two mixer blades rotate. The mixer blades are matched to the geometry of the bowl, and as mixing proceeds, the changing resistance of the dough ingredients is measured as torque on the mixing arms. The measured torque is continuously recorded, the curves indicating the amount of torque, or strength, required to mix the dough to a defined consistency and the length of time the torque stays steady (see Fig 1, right). This process provides an indication of the resilience of the gluten protein matrix that develops and is important in giving the cooked pasta its firmness and cohesive texture. Another purpose of the test is to estimate the water absorption capacity of the semolina, that is, the amount of water required for the dough to reach a defined consistency.
Standard physical dough methods are limited by the long time required for the tests, low energy used to mix the dough (which may fail to properly mix durum semolina dough and develop the gluten) and the relatively large amount of water that needs to be added to the dough (which is not representative of the amount of water added during commercial pasta production). In addition, the standard methods are not representative of commercial pasta dough mixing conditions.
NEW HIGH ENERGY MIXING METHODS
Mixing properties are affected by protein quality, protein content and semolina granulation. Using standardized methods, semolina makes strong dough that resist the stress of mixing, producing flat curves with indistinct peaks that are difficult to analyze and don’t differentiate adequately between semolina flours of different quality.
There is a need for testing at higher energy input that will produce more rapid, accurate and relevant results. Higher energy mixing would be capable of adequately mixing the semolina flour dough to differentiate between samples of different quality. Methods that can mimic commercial mixing conditions would offer considerable advantages when specifying semolina for end users.
The doughLAB is a relatively new instrument for testing dough-making properties. It was designed to emulate the high work rates of modern dough mixers. High-speed (180 rpm) mixing is used to screen semolina samples for suitability in pasta production, mixing at torques around 7.8 Nm, yielding high energy input rates. This feature is especially useful for samples such as semolina that are difficult to develop.
A recently published test evaluated 20 semolina samples using a high-energy input, high-speed doughLAB mixing profile relevant to semolina end use for pasta manufacture (see Fig 2,below). Tests at higher speeds reduced test time by half were more repeatable when compared to standard tests. The test gave a better mixing peak resolution and a better indication of dough stability or resistance to over-mixing.
This accelerated test for difficult-to-develop samples demonstrates the need to modify the existing standard method by increasing the mixing speed. Tests at higher speeds not only mimic process relevant conditions, they also reduce test time for the miller.
NEW LOW WATER ABSORPTION MIXING METHODS
Constituents other than gluten will have an effect on the dough. Starch, sugars, polysaccharides, lipids, flour enzymes, pentosans and water play a key part in the formation of dough. During milling, some of the starch granules will be damaged, greatly increasing water absorption and becoming available to starch degrading enzymes which tend to soften dough.
Just the right amount of water during processing is critical to ultimate quality pasta, so accurately knowing semolina water absorption would be of great benefit to a pasta manufacturer. If dough is too wet, the pasta is extruded too fast and control of shapes is particularly difficult. Wet pasta also requires prolonged drying times which may result in brittle or fragile pasta, and the pasta might not retain its shape during drying. Conversely, dry dough is difficult to extrude, not cohesive because a gluten network is not formed, may be fragile and difficult to mold, and the final product may have cracks.
Standard physical dough test methods require typical water addition in the range 58% to 66%, relevant to bread dough. This is a long way from the typical water addition for pasta dough, which is in the range 30% to 35%. There is a need for testing at lower water additions to an optimum consistency that will produce more process relevant information about the production and behavior of semolina dough. The optimum consistency to choose for the physical dough test should correspond to the optimum consistency of the dough for processing. The judgment of the optimum dough consistency is heavily dependent on both the pasta-making method and the commercial dough processing equipment being used.
A doughLAB water-ladder-type experiment with semolina was run down to 30% water addition, demonstrating that the doughLAB can handle the type of low water dough used for pasta production. The bowl configuration and high rate of addition of mechanical energy enables the low-water semolina dough to mix and develop.
As customers become more discriminating in their quality requirements, particularly for premium products, and variability in product quality is becoming less acceptable, producers are under increasing pressure to supply pasta with quality that is consistent over time. Employing the doughLAB for laboratory testing of pasta dough using energy input and water addition conditions that are relevant to the pasta production process enables the pasta manufacturer to select the correct processing conditions required to produce the best quality pasta.
Bronwyn Elliott is commercial product manager for Perten Instruments of Australia. She may be contacted at firstname.lastname@example.org.