Flour Analysis for Bakery Operations

The pre-eminence of wheat in the production of bread, small baked products and fine pastry is based upon its gluten formation capabilities.

Wheat gluten is formed from the flour protein substances gliadin and glutenin that ‘gelatinise’ during kneading and upon addition of water, and create a three-dimensional network.

During the kneading process, wheat gluten absorbs and binds up to 2-3 times its own weight in water. The swollen, elastic gluten gives the dough a bond. It makes it expandable and pliable, makes it rise and gives it leavening ability. During baking, the wheat gluten congeals and together with the gelatinising starch forms the crumb structure.

The baking behaviour of wheat flour is determined first of all by its physical dough properties. For this reason, the emphasis during wheat flour analyses has to be not only on the determination of the quantity and quality of the ingredients, but above all, on examining the dough characteristics during the kneading process.

In contrast to wheat flour, rye flour only has a low level of gluten-forming properties. For this reason, rye flour dough has a lower gas retention capacity. Rye flour is characterised by its large volume of water-binding mucilage  – pentosan – that makes it possible to achieve much higher dough yield. Rye flour also contains more starch with lower gelatinisation temperatures (50-70°C) than wheat flour (60-90 °C).

As the enzymatic optimum lies within the rye flour’s gelatinisation temperature range, a major part of the rye starch can be broken down into dextrins and soluble sugars. These are now no longer in a position to retain the formerly bound dough water. This breakdown of starch in the course of the baking process can take on a serious dimension in the case of very large enzymatic activity and lead to bread faults such as water stripes and an inelastic crumb.

Rye flour analyses concentrate primarily on an assessment of enzymatic activity and starch gelatinisation.

Moisture Content

The storability of flour is closely linked to its moisture content. The oven drying method (ICC Standard no. 110/1) is generally used as analysis method to determine the moisture content of a particular type of flour. With this method, a precisely weighed quantity of flour is subjected to a specific drying time and temperature. The moisture content of the flour (in percent) is determined from the drying loss which is established through weighing.

The moisture content can be determined more easily with quick analysis methods such as ‘Aqua-Part’ or ‘NIR’ methods.

High moisture contents shorten the storage life of flour and reduce its dough yield. Flour with a high moisture content tends to go lumpy. The moisture content of the flour should therefore not be higher than 15 percent.

Type Number

According to DIN 10355, milling products from bread cereals may only be marketed  according to specific types.

The flour type is the measurement index for the mineral content (formerly ash content) of the flour that remains after incineration and is in close relationship to the milling yield / extraction rate.

To determine the type number, the flour is incinerated in a furnace (muffle furnace) at 900°C for as long as necessary until there remains a white flowing residue consisting of minerals (ICC Standard No. 104/1). The type number indicates how many grams of minerals and/or ash are there in 100 kg of water-free flour.

The minerals can mainly be found in the rim areas of the cereal grain. The volume of minerals increases more and more in line with the intensification of milling. At the same time, there is an increase in the content of proteins, dietary fibres, fats and enzymes, whilst the gluten and starch content decreases proportionately.

In practice, dark, high mineral-content flour is characterised by high water absorption and enzyme activity. In comparison with lighter flour with lower mineral content, it achieves a smaller baking volume. Coarse wholemeal contains all the components of the cereal grain with the exception of the wheat germ and the outer shell.

For this reason, wholemeal, as very coarse milling product, has the highest type number. Whole-grain flour contains all the components of the cleaned, whole grain – including the wheat germ. For this reason, it is not subject to type rating. The grains may be separated from the outer shell prior to processing.

The author is the MD of König Laminiertechnik GmbH. He is a Food Technologist with 35 years experience in bakery technology.

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