FLOUR QUALITY ANALYSIS

Career transition hindered me to write for awhile, now I’m part of food manufacturing company that is trademark for French breads. Though, I have been in food business for more than a decade, bread production is a new genre for me. Baking might mirror a simple process but understanding technical aspect from raw materials, processes to finished goods is like Yeast – that causes ferment and agitation to create quality breads.

Flour is the heart and soul of bread production – quality flour is every bakers demand! I had the chance to attend a seminar on Flour Quality Analysis by one of Philippines’ flour milling company. Attendees are from technical services, quality assurance department, research and development with aim to understand flour quality parameters, standards and procedure enabling us to speak in one language in terms of flour technology in relation to food business.

Background study – Flour Milling is an art or process of separating endosperm from bran and milling the whole endosperm into flour. There are three (3) parts to a wheat kernel (sometimes called a wheat berry): The BRAN is the hard outer covering of the wheat kernel, high in fiber and nutrients; the GERM is the nutrient-rich embryo that will sprout and grow into a new wheat plant; and the ENDOSPERM is the biggest part (80 -83%), the “inside” of the kernel – mostly starch. Take note that white flour is made from the endosperm only and not whole grain. While, Whole Wheat Flour is combination of all 3 parts of the whole berry (whole grain).

Four Major Systems of Operation in Flour Milling Process: First, Breaking system – the function of the first three breaks is to open up the wheat and break off the bulk endosperm and sizes it suitably. The last two breaks scrape off the remaining endosperm from bran as clean as possible. Second, Purification system – is a process concerned with separating of bran particles from good endosperm stock. Purifiers also grade endosperm stock into various size particle ranges for efficient reduction or grinding. Third, Reduction system – is to grind the purified endosperm into flour of desired fineness and as to uniform granulation as possible without excessive damage to starch granules or gluten quality. Lastly, the Sifting system – is classifying or sourcing out of ground stocks mostly coming from break and reduction systems according to size or granulation.

After yielding Flour as end product its time to test quality to determine how this flour will perform in bakery according to customer’s specifications and how consistent flour quality; during our training limitations we’re set: There are limitations to flour specifications, flour specifications only give an indication to quality, flour quality cannot guarantee quality due to variations in shop conditions, and, there are variations due to weather and human induced conditions. For customers get what he wants, first, the baker needs to understand his needs. Second, he needs to understand what tests his flour suppliers do. Third, co-relate his needs with the flour test done by millers. Lastly, specify the flour he wants.

In general, a bakery or customer’s flour specification requires physical, analytical, rheological, microbiological, nutritional and functional.  For Physical Specifications, this includes general description, wheat mix, color, odor and foreign material. Under physical the most critical parameter is the color since color often affects the color of the finished product. Generally speaking, bright white color flour is more desirable for many products. Color testing is subjective through visual inspection, thus, for a more qualitative and acceptable result – the Minolta Chroma Meter Test is one reliable method. This method reminds me of spectrophotometer in terms of technology wherein flour color results are reported in terms of 3-dimensional color values. Sample of flour is placed on granular materials attachment and compacted. The Minolta Chroma Meter is inserted into the granular materials attachment, then, flour color is determined by measuring the L value or whiteness. In Europe, bakers prefers darker to yellowish color of flour as they believe the more whiter the more additives was involved altering quality.

Analytical Specifications is more technical, most food industry has no resources to determine actual value of moisture content, ash, protein, enzymatic activity and oxidation treatment. Thus, most of us relay on submitted Certificate of Analysis. Protein content is the most important measurable flour characteristic; it is responsible for the formation of the framework of the baked product since it is related to many processing properties, such as water absorption and gluten strength. Protein content can also related to finished product attributes, such as texture and appearance. Protein content is determined through Kejldahl process or high temperature combustion in a protein analyzer. Since protein is the major wheat compound that contains Nitrogen, the protein content can be determined by measuring the amount of Nitrogen released during burning.

Gluten is responsible for the elasticity and extensibility characteristics of flour dough, the very reason wet gluten is common flour specification required by end users in the food industry. When I was in Universal Robina Corporation, I conduct daily wet gluten analysis for flour to be used in manufacturing crackers to provide information on the quantity and estimate the quality of gluten in flour sample. The manual method requires approximately 2 hours completing the test and your hands literally on labor. Thank heaven for technology with the invention of Glutomatic/Machine-washed that within 20 minutes accurate gluten percentage is provided. The procedure is to wash the flour sample with salt solution to remove the starch and other soluble; the residue remaining after washing is the wet gluten. During centrifugation, the gluten is forced through a sieve. The percentage of gluten remaining on the sieve is defined as the gluten index, which is an indication of gluten strength. A high gluten index indicates strong gluten.

Ash is the mineral residue remaining after incinerating a small amount of flour; ash provides an estimate of the degree of separation of bran and germ from the endosperm. Since ash is primarily concentrated in the bran, ash content in flour is an indication of the yield that can be expected during milling. For Ash Test Method, a sample of flour or ground wheat (approximately 5 grams) is weighed and placed in ash cup. The sample is heated at 585^oC – 600^oC n ash furnace until its weight is stable (usually overnight). Then, the residue is cooled to room temperature and then weighed.

Determining moisture content is an essential first step in analyzing wheat or flour quality since this data is used for other tests. Flour millers adjust the moisture content in wheat to standard level milling as indicator of grain storability and profitability. Moisture Test Method – a small sample of flour (2 grams) is weighed and placed in a moisture dish; the sample is heated at 135^oC in an air oven for 2 hours and then sample is cooled to room temperature and residue is weighed. There is more convenient and faster way to determine moisture content through Infrared Moisture analyzers that guarantee result in less than 10 minutes.

The falling number instrument analyzes viscosity by measuring the resistance of a flour and water paste to a falling stirrer. Since starch provides the supporting structure of bread, too much activity results in sticky dough during processing and poor texture in the finished product. A high falling number (for example, above 300 seconds) indicates minimal enzymes activity and sound quality flour, while, a low falling number (for example below 250 seconds) indicates substantial enzymes activity and sprout-damaged flour.  

Rheological means mix-study of flour sample with water for Farinograph, Extensigraph, Alveograph and Amylograph tests. Farinograph determines dough and gluten properties of flour by measuring the resistance of the dough against the mixing action of the paddles. Results include absorption, arrival time (indicates the rate of flour hydration), stability time (indicates the time dough maintains maximum consistency), peak time (indicates dough development time, beginning the moment water is added until dough reaches maximum consistency), departure time and mixing tolerance index. The method requires a 50 or 300 grams flour sample on a 14% moisture basis and placed into the corresponding farinograph mixing bowl; water from a burette is added to the flour and mixed to form dough; as the dough is mixed, the farinigraph records a curve on a graph paper.

Weak Gluten Flour has a lower water absorption, shorter peak or development time, shorter stability time, shorter time to breakdown, and greater MTI or degree of softening during mixing that strong gluten flour. The Farinograph Test is one of the most commonly used flour quality tests in the world. The results are used as parameters in formulation: to estimate the amount of water required to make dough, to evaluate the effects of ingredients on mixing properties, to evaluate flour blending requirements, and to check flour uniformity.

Extensigraph determines the resistance and extensibility of dough by measuring the force required to stretch the dough with a hook until it breaks. Extensigraph results includes resistance to extension, extensibility, and area under the curve used as parameters in formulation: to evaluate the dough behavior due to fermentation, to evaluate the effects of additives on dough behavior, to evaluate flour blending requirements, and to check flour uniformity.

The Amylograph Test measures four starch properties and enzyme activity which results from sprout damage (alpha amylase enzyme activity); sprouting in wheat, as indicated by high enzyme activity, produces sticky dough that can cause problems during processing and results in products with poor color and texture. For Asian noodle products, flour of medium to high peak viscosity is preferred because it gives noodles better texture characteristics. The method requires 65g flour sample combined with 450ml distilled water and mixed to make a slurry; the slurry is stirred while being heated in the amylogrpah, beginning at 300^oC and increasing at a constant rate of 1.5^oC per minute until the slurry reaches 95^oC. The amylograph records the resistance to stirring as a viscosity curve on graph paper.

Its time now to review our test method procedures and update methodology for flour analysis.