What are Grain-based Flours?
Grain-based flours are powders produced by reducing grains to small particle sizes. They are used primarily for making breads, cookies, cakes, pastries and other baked goods.
Grain flours are commercially-available in two main forms:
- Whole flours which contain the grain’s endosperm, germ and bran fractions
- Refined flours which contain only the endosperm fraction
There is a wide variety of grain-based flours with wheat being the most-globally consumed. Corn is prevalent in the U.S., Latin America and some Asian countries while rye flour is a basic component of East and Central European baked goods.
Commonly used grain flours can be classified into gluten- and non-gluten containing types:
|Grains containing gluten||Grains not containing gluten|
Producing flours from grains is an ancient practice which is believed to have originated around 6000 BC. Scenes of milling and baking can still be seen on the walls of Egyptian tombs dating back to 2600 BC.
Earlier flour grinding systems were cone mills which developed into stone mills. Roller mills were invented in 1865 in Hungary while the first steam mill was built in England in 1879. Jet milling is one of the newest technological advances for making superfine flours.1
Typical composition of common grain-based flours:*
|Flour||Protein (%)||Fat (%)||Carbohydrates/total sugars (%)||Fiber (%)||Energy (Kcal)|
|Wheat||11.8||1.1||70.7 / 1.4||12.6||345|
|Rye (medium color)||10.88||1.52||75.43||11.8||349|
*USDA Branded Food Products Database, July 2018 & other sources3
Flour composition varies significantly with the grain’s cultivar, milling process, flour extraction rate among others.
Grain milling uses two approaches:
- Break open kernel to separate the endosperm from bran (principle of roller milling). It involves multiple grinding and separation steps from sifting to aspiration and gravity separation.
- Decortication/degermination and transforming the endosperm to grits or flour. Typically used with maize and sorghum.
Modern milling operations consist of:
- Cleaning the kernels to remove extraneous material.
- Tempering and moisture adjusting to toughen the bran and make the germ more pliable so the endosperm is easily separated.
- Breaking/crushing the kernels between corrugated rollers, loosening the endosperm from the bran and germ.
- Separating or purifying the endosperm from the bran and the germ, using sieves and air currents to produce middlings.
- Grinding the middlings into flour between a series of smooth, reduction rollers.
Steps 3, 4 and 5 can be repeated several times to generate flour streams where each progressive stream contains less endosperm and more bran and germ impurities than the last. These streams are selectively combined and sifted to produce commercial grades of flour. The flour is then naturally aged or treated with bleaching and maturing agents. Production of whole wheat flours requires unique systems to prevent lipid deterioration due to rancidity.
Ancient grains such as spelt, Khorasan and emmer have vitreous and hard kernels with high ash content. They produce flours with low yield. Barley milling challenges are similar to those of ancient grains.
Triticale grains are milled using standard wheat flour milling techniques. However, its low milling efficiency caused by the grain morphology (shriveled, long, deep creases and soft endosperm) can be improved by co-milling triticale with wheat3
Millet and sorghum are decorticated prior to grinding. Roller milling produces whole wheat flour, semi-refined and a bran-rich fraction. Finely-ground particles are sifted after each pass. One major challenge with sorghum is the presence of starch granules in the mesocarp which makes the pericarp very friable.
Oat kernels have outer and inner hulls which should be removed prior to grinding and groat cutting and separation. The berries or groats are hulled, heat-treated to soften them and inactivate the lipases. Groats are scoured/polished with special brushes clean the groats. Pearling step for de-branning and pre-processing to improve flour yield and eliminating breakage and reducing microbial decontamination. The flour and bran system produces whole oat flour, or a combination of low bran oat flour and oat bran.
Rye is milled similar to wheat. A quick tempering step is needed to loosen the bran. For producing rye flour, finely corrugated break rolls are placed much closer than in wheat milling.
Corn flour milling following the old process consists of preparing cornmeal by grinding the whole corn kernel after removing the bran coat. Newer processes call for degerminating to reduce rancidity and bran removal followed by milling
Performance of grain-based flours in bread formulations is summarized below:
|Wheat||Elastic and extensible||Good volume and fine crumb|
|Spelt||Inelastic and sticky||Dense (e.g. German Oberschwäbische Seelen)|
|Khorasan||Sticky and crumbly with high water absorption||Dense and low volume. Adaptable to quick bread|
|Emmer||Sticky with high water absorption, can be overmixed easily.||Dense and low volume bread.|
|Triticale||Weak, inextensible. High alpha-amylase makes dough develop very quickly. Less tolerant to mixing.||Best with unleavened breads. Composites with wheat flour up to 40% makes good quality bread.|
|Rye||Rye gluten is less elastic than wheat. It holds less gas during leavening; dough should be acidic or sourdough style for better development.||Compact and dense. Suitable for sourdough, pumpernickel breads and gingerbread.|
|Barley||Ruptures easily but can retain moisture in yeast-raised and quick bread doughs.||Hard and less cohesive crumb. Sweet nutty taste. Best for unleavened breads. Suitable for sourdough method and as a composite with wheat flour.|
Non-gluten containing flours
|Oat||Whole oats flour has high water absorption, long development time and low dough stability.||Nutty and pleasant tasting. Up to 10% composite with wheat flour produces acceptable bread.|
|Corn||dough wetting and mixing are easier than wheat flour||10% corn flour wheat composite provides nutty flavor and a golden yellow color. Works well in quick breads and other baked goods.|
|Millet||Sticky and weak dough (low workability, hard, high water absorption||Hard texture with nutty flavor. Best in unleavened type, Chapatti.|
|Quinoa||Poor dough mixing quality (high alpha amylase activity).||Acceptable breads up to 10% composites with wheat flour. Better breads can be prepared with sourdough fermentation.|
- Walker, G. ‘List of machinery in Caudwell Mill’ 2002; CAUD-06916.
- Peña, R. and Amaya, A. Milling and breadmaking properties of wheat triticale grain blend. J. sci. Food Agric., 1992, 60, 4, pp: 483-487.
- USDA Branded Food Products Database, July 2018. https://ndb.nal.usda.gov/ndb/foods/show/45093121?fgcd=&manu=&format=&count=&max=25&offset=&sort=default&order=asc&qlookup=spelt+flour&ds=&qt=&qp=&qa=&qn=&q=&ing=