OATS PROCESSING, MILLING

INTRODUCTION

The oat (Avena sativa) is a species of cereal grain grown for its seed. While oats are suitable for human consumption as oatmeal and oat milk, one of the most common uses is as livestock feed.

Oats are associated with lower blood cholesterol when consumed regularly.

Origin and Cultivation

Genetic evidence shows the ancestral forms of A. sterilis grew in the Fertile Crescent of the Near East. Oats are usually considered a secondary crop, i.e., derived from a weed of the primary cereal domesticates, then spreading westward into cooler, wetter areas favorable for oats, eventually leading to their domestication in regions of the Middle East and Europe.

Oats are best grown in temperate regions. They have a lower summer heat requirement and greater tolerance of rain than other cereals, such as wheat, rye or barley, so they are particularly important in areas with cool, wet summers, such as Northwest Europe and even Iceland. Oats are an annual plant, and can be planted either in autumn (for late summer harvest) or in the spring (for early autumn

harvest).

Production

In 2018, global production of oats was 23 million tonnes, an 11% decrease from 2017. Production was led by Russia with 20% of the world total and Canada with 15% (table). Other substantial producers were Spain, Australia, Poland, and China, each with over one million tonnes.

Uses

Oats have numerous uses in foods; most commonly, they are rolled or crushed into oatmeal, or ground into fine oat flour. Oatmeal is chiefly eaten as porridge, but may also be used in a variety of baked goods, such as oatcakes, oatmeal cookies and oat bread. Oats are also an ingredient in many cold cereals, in particular muesli and granola. Oats are also used for production of milk substitutes ("oat milk").Oats are also widely used as a thickener in soups, as barley or rice .Oats are also commonly used as feed for horses when extra carbohydrates and the subsequent boost in energy are required.

Nutritional value

Oats contain diverse essential nutrients. In a 100-gram serving, oats provide 389 kilocalories of food energy and are a rich source of protein (17%), 66% carbohydrates, including 11% dietary fiber and 4% beta-glucans, 7% fat, several B vitamins and numerous dietary minerals, especially manganese.The established property of their cholesterol-lowering effectshas led to acceptance of oats as a health food.

PROCESSING OF OATS

Oats processing is a relatively simple process. It includes following steps:

Cleaning and sizing

Upon delivery to the milling plant, the oats are cleaned, removing the chaff and items such as rocks, metal, oversized materials, and other grains. Oats of different sizes de-hull at differing velocities. So, once impurities have been removed, the raw oats are separated by width and length into different classifications before de-hulling.

Dehulling

Centrifugal acceleration is used to separate the outer hull from the inner oat groat. Oats are fed by gravity onto the centre of a horizontally spinning impeller, which accelerates them towards an outer mill ring. Groats and hulls are separated on impact. The lighter oat hulls are then aspirated away, while the denser oat groats are taken to the next step of processing. Oat hulls can be used as feed or as a biomass fuel and are often used within the oat processing line to power solid fuel boilers for steam and power

generation. Excess oat hulls are generally pelletised before being provided as feed.

Kilning

The unsized oat groats pass through a heat and moisture treatment to balance moisture for optimal storage conditions and to deactivate self catalysing enzyme activity. Oat groats are high in fat (lipids) and once removed from their protective hulls and exposed to air, enzymatic (lipase) activity begins to break down the fat into free fatty acids, ultimately causing an off-flavour or rancidity. Depending on temperature, humidity and moisture content, de-hulled oats can begin to show signs of enzymatic rancidity rapidly if not stabilized. This process is primarily done in food-grade plants, not in feed-grade plants. Groats are not considered raw if they have gone through this process; the heat disrupts the germ and they cannot sprout.

Sizing of groats

Many whole oat groats break during the dehulling process, leaving the following types of groats to be sized and separated for further processing: whole oat groats, coarse steel cut groats, steel cut groats, and fine steel cut groats. Groats are sized and separated using screens, shakers and indent screens. After the whole oat groats are separated, the remaining broken groats get sized again into the three groups (coarse, regular, fine), and then stored. "Steel cut" refers to all sized or cut groats. When not enough broken groats are available to size for further processing, whole oat groats are sent to a cutting unit with steel blades that evenly cut groats into the three sizes above.

Final processing

Three methods are used to make the finished product:

1) Flaking

This process uses two large smooth or corrugated rolls spinning at the same speed in opposite directions at a controlled distance, before which the cut groats are conditioned for flaking via steam injection.

After flaking, the oats are then dried to a sufficient moisture for storage and transport. Oat flake thickness is a key control point dependant of the type of oat flakes to be produced. Typically, the flakes produced are either instant, quick or traditional whole rolled oats and range in size from 0.4 mm to 1 mm.

2) Oat bran milling

This process takes the oat groats through several roll stands to flatten and separate the bran from the flour (endosperm). The two separate products (flour and bran) get sifted through a gyrating sifter screen to further separate them. The final products are oat bran and debranned oat flour.

3) Whole flour milling

This process takes oat groats straight to a grinding unit (stone or hammer mill) and then over sifter screens to separate the coarse flour and final whole oat flour. The coarser flour is sent back to the grinding unit until it is ground fine enough to be whole oat flour. This method is used often in India and other countries. In India, whole grain oat flour (jai) is used to make Indian bread known as jarobra in Himachal Pradesh.

Preparation at home

Oat flour can be ground for small scale use by pulsing rolled oats or old-fashioned (not quick) oats in a food processor or spice mill.