Quality control and laboratory in milling

05 January 201813 min reading

“Although flour is a non-perishable food the manufacturer should treat quality control as an important factor for success and safety measures should be taken into consideration starting from the wheat receiving throughout the flour dispatch.”


Sarah Krayem

Technical Director National Flour Mills S.A.R.L (Part of Essa Al-Ghurair Investment)

Many milling companies are competing in the market. The companies that are investing in quality departments to improve the quality of their final products and meeting customer’s expectations have an outstanding profile to gain a major position in the market.

Pick a product at random and list its attributes. It is no surprise that quality is one of the main aspects of that product or any other product that comes to mind. The importance of quality, therefore, is due to its essential presence of which no product can exist. Quality plays the main role in determining what a product is and where it is placed and positioned whether at a marketing quadrant or a competitive frontier.

That being said, the importance of quality gets to its peak of importance when the product has an effect on human lives; whereas quality becomes the safety. Nonetheless, “Wheat Flour” the widest staple food and the product of concern in this article, is one of the most basic and essential food ingredient making its quality a food safety and a human well-being issue. With the increase in consumer’s awareness, manufacturers excel through more transparency and are more persistent in offering the best quality their customers always look for. For the purpose of this article, we will divide flour quality into three main attributes we call the SSS: Safe, Sustainable, & Standard.

SAFETY We start with “Safe” since this is the attribute that cannot tolerate any compromise.

Although flour is a non-perishable food and requires more processing before final consumption, the manufacturer should treat this as an important factor for success and safety measures should be taken into consideration starting from the wheat receiving throughout the flour dispatch.

STANDARD As wheat flour is a primary raw material and a staple food, it has standards which the producers must follow. Hence, wheat flour has to strictly meet 3 major sets of standards: regulatory, consumer and producer.

Regulatory such as governmental standards, consumer-related such as baking property standards and producers such as yield standards.In particular, we are following the Lebanese standards established for wheat and wheat flour. We also take into account every new ministerial decision and regulation. In addition, to best control these stages, National Flour Mills was the first Lebanese mill to establish a food safety management system in 2008 and earn the ISO22000 certification. Until today, we are still working on improving the system from a year to another.

Furthermore, the final product standards should not only meet legislations, but they should also be as per our customer’s specifications. That’s why our different final products undergo quality control; it is a must for us to ensure that we are offering our customers the quality they are asking for (Alveograph W and baking strength, protein content, ash content, retrogradation and shelf-life …)

Producers also draw their own standards according to their process, equipment used, profit margin, extraction rates, yield, and consistency.

SUSTAINABILITY Strategic sustainable solutions are a key feature for a sustainable relationship with our customers. This attribute differs from one miller to another and plays an important role in making or breaking the business.

At National Flour Mills for instance, we give full attention for our customers and we work more closely with them towards fulfilling their needs and commit to providing them with the consistent final product; thus the need of a cooperative effort between the departments of our milling company and the quality control department. On one hand, the baker is asking for tailor-made solutions dictated by his process, his logistic needs and the final product he intends to serve; which bring challenges to the miller that could be resolved by: • Knowing more about the raw material, • Controlling the process by analyzing the flour produced, • Analyzing efficiently these data from different quality values • And using scientific techniques and tools to ensure sustainable product.

On the other hand, the customer should take into consideration the constraints of the miller in order to reach a win-win sustainable solution. This is why constructive communication is our best partner in building the trust and strengthening our relationship with our customers.

Therefore, millers should consider “quality control” the core of their milling operations; ideally playing the communication role among departments and centered equidistantly from the producer, the legislator, and the customer.

While many milling companies are competing, one should have an outstanding profile to gain a major position in the market. Such companies are investing in quality departments to improve the quality of their final product and they have been able to meet customer’s expectations, instead of exceeding them.

In addition, the quality control department at NFM played an essential role in research & development bringing the company forward into a leading position. In this particular case, the QC department worked closely with the technology provider (Bühler AG) in optimizing the first milling technology in the world: the Combi PesaMill™ providing a flexible process of producing 3 types of flour: Atta whole wheat flour, type 850 and baker’s flour.

This is where quality control department played a key role in this phase. We were supporting the Bühler team with all the required lab analysis to characterize the products produced by the new mill (water absorption, starch damage, granularity, moisture content…). This helped them optimize the mill performance and make all the modifications required to the milling process in order to achieve the target quality of flour. Previously, only available with Chakki stone mills, Atta whole wheat flour is now produced at NFM in an energy efficient, most hygienic industrial process.

For the quality control to achieve the mentioned above roles, responsibilities and added values; and to do it consistently persistently and scientifically, a well-equipped laboratory is essential. So we cannot tell how does an ideal flour mill lab look like, it depends on the company’s vision, financial flexibility, investment ability and many other factors.

However, we can mention the most important quality characteristics coupled with the needed quality control equipment, significant in a modern laboratory within a milling company.

MOISTURE Quality control starts when the wheat is received at the mill. And before any measurement, a visual inspection should be done to ensure that the wheat is safe and suitable for processing for human consumption. In addition, it should be free from abnormal flavours, odors, living insects and mites [1]. Moreover, determining moisture content is an essential first step in analyzing wheat or flour quality since this data is used for other tests [3]. The moisture content of flour is most easily determined from the difference in weight of a sample before and after drying in an air oven [2]. While the reference method is time-consuming, and many samples should be tested within one shift; NIR spectrophotometer and halogen moisture analyzer is also used for measuring moisture content at a very short period of time. One should also consider the maintenance of this equipment and a follow-up calibration schedule should be established to ensure the good reading of the machines.

Despite that moisture content can be an indicator of profitability in milling, moisture content should not exceed 14.5 % because it attracts mold, bacteria, and insects, all of which cause deterioration and might lead to foodborne illnesses. Wheat or flour with low moisture content is more stable during storage; hence the need of controlling the moisture content of wheat upon the receiving and flour during the milling process [3].

TEST WEIGHT Test weight is a measure of the weight of grain per unit volume in kilograms per hectoliter (kg/hl) or pounds per bushel (lb/bu). Millers are interested in test weight of the grain because it is normally correlated with greater milling flour yield and lower test weights resulting from shriveled and less sound kernels result in lower flour yields [2]. That’s why a chondrometer should be present in a laboratory mill so that the miller forecast the behavior of the wheat received and extraction rates.

EXPERIMENTAL MILLING Flour yield is dependent on the amount of endosperm in the kernel and how well it can be separated from the bran. This can be evaluated by a laboratory scale experimental milling by using a Bühler MLU-202 experimental mill [2]. Yet, any other laboratory mill could be used for experimental milling not only to give significant information about the milling quality of the wheat used but to also provide information about flour quality evaluation [2].

ASH The major components of the wheat kernel are the outer covering of bran, the embryo or germ, and the endosperm. The goal of flour milling is to separate these three as cleanly as possible, along with reducing the endosperm into flour particles. Higher extraction rates of flour, while economically desirable, may result in flour with excessive bran contamination (and thereby higher ash content) as well as increased starch damage. Therefore, a proper balance needs to be achieved, depending on the desired end use of the flour [2]. However, studies have shown that the ash contamination inside the endosperm might vary among wheat genotypes. That’s why it is not always correlated with the degree of bran and might come from different sources [2] (flour fortification, ineffective cleaning of wheat that does not prevent foreign seeds of passing through the milling process…)

It can be determined by incinerating a flour sample in a muffle furnace, leaving only the ash [2]. Along with the reference method, we can also use one more time the NIR spectrophotometry for ash detection as it is a time-effective alternative for the reference method.

WHITENESS In order to decrease the human error in evaluating the color of the flour produced, Minolta colorimeter could be used as the reference method for measuring the brightness of the flour and monitoring the fluctuation of the color parameters. It is used for the standardization and quality control inspection and for determining the specification of the final product’s color.

PROTEIN Protein content is a major specification for millers at buying stage since it is directly related to water absorption, gluten content and its strength. Low protein content is desired for crisp or tender products, such as snacks or cakes and high protein content is desired for products with a chewy texture, such as pan bread and hearth bread [3]. For this reason, protein determination is very important for millers in order to classify their wheat and use each type for the production of the right type of flour.

It is typically determined indirectly through measuring nitrogen content by methods such as Kjeldahl (AACCI Method 46-11A) and combustion (AACCI Method 46-30). A correction factor accounting for amino acid composition and nonprotein nitrogen (x 5.7) is then applied to calculate the protein content [2].

On more time, NIR spectrophotometer could also be used for protein determining by calibrating it to either reference methods; it is less time consuming and avoid the analyst of being exposed to chemicals and reagents [2].

FALLING NUMBER Baked goods quality is affected by the alpha-amylase activity measured by the Hagberg Falling Number® System. Since starch provides the supporting structure of bread, too much alpha-amylase activity results in the sticky dough during processing and poor texture in the finished product. If the falling number is too high, enzymes can be added to the flour in various ways to compensate. However, if the falling number is too low, enzymes cannot be extracted from the wheat flour which makes it impractical [3].

DAMAGE STARCH During the grinding process, starch granules are damaged to some degree depending on the hardness of the grain, wheat preparation, and mill configuration. Once damaged, the water absorption capacity of starch increases tenfold. It is a critical constituent in determining the mixing properties of dough. Damaged starch, therefore, has a direct effect on the behavior of dough during fermentation. Its action will have an influence not only on the volume of the finished product but also on its color.Failure to control the levels of damaged starch may cause a number of issues at the stage of transforming flour into cooked products. SDmatic is today the fastest solution developed by Chopin Technologies for measuring the starch damage according to the amperometric method.

WET GLUTEN This test is commonly practiced in any laboratory within the milling industry. As the wet gluten is formed by the glutenin and gliadin, each respectively is responsible for the elasticity and the extensibility of the dough. It represents one of the most important characteristics of wheat flour and that must be measured by the Glutomatic® System by determining the gluten content and the gluten index explaining the quantity and the quality of wet gluten [3].

RHEOLOGICAL ANALYSIS The importance of dough rheology is well recognized in predicting and controlling the quality of baked products. Variation in the elastic and viscous behavior of different wheat flour doughs is considered as primary quality factors in bakery applications. The primary aim of rheological measurements remains to differentiate between wheat varieties according to their baking performance without actually performing the baking test. Rheological tests that can correctly predict the baking performance of any wheat variety would save time, material and labor.

It is a well-known fact that the mechanical properties of wheat flour doughs, determined empirically by the Farinograph, Extensograph and Mixograph and Alveograph instruments, play a significant role in the handling properties of dough during processing and in the quality attributes of the finished products. Tests based on these instruments are useful for providing practical information for the baking industries while they are not sufficient for interpreting the fundamental behavior of dough processing and baking quality (Dobraszczyk, 2003).

BAKING TEST To make sufficient interpretation and because it is more convenient for the customer to get consistent flour without any changes in his recipes, we as millers should conduct experimental baking trials in order to ensure the consistency of our products. And by applying these trials, we forecast the customer’s evaluation of volume, color, appearance, and texture.

Baking tests provide the end-users with information on flour quality characteristics [3].

In addition, these tests provide information that can be used to optimize processing conditions prior to commercial-scale baking [3].

Achieving baking objectives is done by evaluating: • The balance between gluten strength and dough extensibility during processing [3] • The dough machinability • The fermentation process at different conditions • The effect of using additives and flour corrector solutions • And last but not least sensory attributes of the baked goods.

References: • [1] Codex Standard 199-1995, STANDARD FOR WHEAT AND DURUM WHEAT, CODEX STAN (199-1995), şuradan alınmıştır:

• [2] Servet, G.S., & Serpil, S. (Eds.). (2008). Food Engineering Aspects of Baking Sweet Goods. By CRC Press. P. 9-10

• [3] Wheat and Flour Testing Methods. (2004). A Guide to Understanding Wheat and Flour Quality”. By the Wheat Marketing Center, Inc. Portland Oregon. ABD.

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