Effect of wheat flour on bread quality
Tuesday, April 22, 2014 08:00 IST
Bread wheat is an important crop worldwide. There are six different classes, or types, of wheat. Each class is used for specific purposes to get the best possible finished product. Hard red wheat is best for yeast breads. Soft wheat is best used in cakes, pastries and other baked goods, as well as crackers and cereal. Durum wheat is the hardest of all wheat and makes the best pasta.
Bread flour is milled primarily for commercial baking use, but can be found at most grocery stores. While similar to all-purpose flour, it has higher gluten content, which is optimal in making yeast breads.
Flour performance depends on its composition, which in turn depends on wheat characteristics and milling.
The quality of bread flour is determined by its ability to produce a consistent finished product with these characteristics:
• High loaf volume;
• Symmetrical loaf shape;
• Attractive and even crust colour;
• Fine and uniform crumb structure;
• Smooth texture;
• Light crumb colour;
• High absorption (moisture content); and
• Tolerance to processing variations.
Wheat flour is made from many components and every component has an effect on the quality of bread. The biggest component of wheat is starch. Protein content is influenced mainly by nitrogen fertilisation, while the protein quality is determined primarily by the wheat genotype. However, both quality and content of the wheat protein are affected by the climatic conditions during wheat maturation. Vitreousness is considered to be related to the endosperm microstructure whereas hardness is suggested to influence the adhesion forces between starch granules and protein matrix. Many studies investigating bread wheat baking performance have addressed protein properties, with particular emphasis on gluten strength. Differences in baking quality among cultivars have been related to differences in gluten composition, particularly to the high molecular weight glutenin subunits.
Factors affecting the quality of bread are:
Wheat and Milling Characteristics
Wheat is classified on the hardness, colour, and growing season of the wheat varieties. Hard wheats have higher protein content than soft wheats and are used mostly for yeast-raised products. Soft wheats are used mostly for chemically leavened products. Colour refers to the red, white, or amber appearance of the bran on the outside of the kernel. Winter wheat is planted in the winter and harvested in early summer. Spring wheat is planted in the spring and harvested in late summer.
Milling separates the bran and germ fractions from the endosperm, which is used to make flour, and reduces endosperm particles to the correct size. A series of separation and sizing steps converts 100 pounds of wheat into about 75 pounds of various flour types. Patent flour is made from the purest endosperm fraction with the lowest bran content. Clear flour is made from less pure fractions and has higher protein and bran content. Straight flour contains all the flour fractions and has a protein and bran content that falls in between the other two.
Ash: It is the mineral residue remaining after organic matter has been incinerated. Wheat bran contains more minerals than does endosperm, so ash content roughly correlates with flour type. Typical ash levels are 0.4 to 0.45 per cent for patent flours, 0.45 to 0.5 per cent for straight flours, and approximately 0.6 per cent for clear flours.
Protein quantity: It is affected primarily by wheat growing conditions. The protein content of flour is usually about 1 per cent less than the wheat from which it was milled and is about 1 per cent lower for patent flour than it is for clear. Typical flour protein levels for bread Products range from 11 to 15 per cent.
Protein quality: It is measured indirectly by dough-testing devices such as Farinograph. It is affected primarily by wheat variety, which determines the characteristics of the glutenin and gliadin fractions of gluten, which make up about 85 per cent of the flour protein. Typical Farinograph stability times for bread flours are 8 to 12 minutes.
Damaged starch: It is created during milling. Higher damaged starch levels increase absorption and the amount of yeast fermentation. Percentage of damaged starch in flour is determined as grams of starch susceptible to hydrolysis by alpha-amylase per 100 gram of flour on a 14 per cent moisture base. Typical damaged starch levels in bread flours are 5 to 10 per cent.
Starch: It is solid forming in the dough and causes the accumulation of water on the surface of dough, fragmentation products are sugars and these sugars are important for the fermentation and the colour of the bread. Dextrins occur on the surface of the bread during baking. The heat becomes yellowish first and then brown. Concentrated vapours and these dextrins get bright because of being put vapour into the oven. Outer part of wheat particle contains the materials, which are not used by human digestive system and those are called as cellulose and pentosan. Celluloses and Pentosans have important properties with respect of bread production process as follows:
Fat: Wheat flour contains 1-2% ratio of fat. Black flours contain more fat than white flours. Fats have positive effects on gluten elasticity. Therefore, it has positive effect on bread quality of fat in the wheat. When wheat flour is burnt, there remains a part called non-combustible and mineral. Mineral stuff ratio in black flours is more rather than white flours. It is not a desirable feature.
- Cellulose and pentosan inflate absorbing big amount of water
- Absorb big amount of water at the stage of dough kneading. Therefore, black flours absorb more water
- Pentosans create gels at the stage of water absorption
- The dough made with flours, which contain a big ratio of wheat bran become sticky and damp and elongation is less. As a result of this, fermentation tolerance of the dough and the ability of gas retention reduce, bread volumes become small
Absorption: It is measured by the Farinograph as an indication of the flour’s ability to hold water while maintaining its consistency. High protein and damaged starch levels give high absorption, which is good for baking performance because it increases the finished product yield and improves shelf life. Typical absorption levels for bread flours are 58 to 66 per cent.
Amylase enzyme activity: It is measured by viscosity tests like the Barbender Amylograph. It is influenced by wheat growing conditions and malting at the mill and is most important in straight lean doughs, where it affects the amount of yeast fermentation. Typical Amylograph values for malted bread flour are 450 to 550 Barbender units.
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Schofield, J.D.1994. Wheat proteins: Structure and functionality in milling and bread making. In Wheat, Production, Properties and Quality;London, UK, 73–106.
Dowell, F.E.; Maghirang, E.B.; Pierce, R.O.; Lookhart, G.L.; Bean, S.R.; Xie, F.; Caley, M.S.; Wilson, J.D.; Seabourn, B.W.; Ram, M.S 2008. Relationship of bread quality to kernel, flour, and dough properties. Cereal Chemistry, 85, 82–91.
(The author is assistant professor, Assocom Institute of Bakery Technology & Management, Uttar Pradesh. She can be contacted at email@example.com)
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