How Are Oats Processed? (Oats To Oatmeal)

Oats are a delicious and versatile pantry ingredient, whether you enjoy overnight oats or oatmeal in the morning, snack on cookies, or order your coffee with oat milk. This gluten-free grain is healthy and full of fiber. But for it to get to your table – have you ever wondered how oats are processed?

Oats must be processed to be edible. The processing includes quality testing, cleaning, dehulling, and kilning or toasting. After being sized, oat groats can be steel-cut, flattened into flakes, or ground into flour. Manufacturers and retailers buy and sell processed oats and their by-products.

Walking through the store, you will notice how many oat products are available. There are steel-cut oats, rolled oats, instant oats, infant oats, granola, snack bars, cookies, oatcakes, and bread. These products are all outcomes of the oat processing industry. Let’s look at how oats are processed and why.

From Oats To Oatmeal: How Oats Are Processed

Without processing, oats aren’t edible – you can’t eat them in their raw form. However, this process doesn’t involve chemicals or additives but procedures to clean, sift, and make the oats digestible.

Three main steps will take your oats from the farm to your table.

Left to right: Oat groats, flakes, bran and flour

Step 1: Testing

Farmers send their harvested raw oats to the mill or plant.

Before the oats are processed, they must be tested to ensure high quality and food safety. Tests include checking for foreign material, insects, moisture content, and weight.

Once the oats have been accepted, they enter the milling phase.

Step 2: Milling

In the milling phase, where the oats are cleaned and preserved to make them safe to eat. Milling has three sub-steps: cleaning, hulling, and kilning.


The first step in processing oats is to clean them:

  • Oats are loaded onto moving trays, so unwanted materials, such as stones, twigs, and other grains, are sieved out. The oats then move through a series of cylindrical meshes to remove ever-smaller contaminants, such as weed seeds, wheat, or barley.
  • The oats also pass through a rotary magnet to remove any metal.
  • A high-intensity spray washes the oats, and a blast of air dries them.


Once the oats are clean, the indigestible and unpalatable husks that cover the edible oat kernels need to be removed.

  • The oats spin through rotating rubber discs that remove the hull without breaking the kernel or groat.
  • A second process, aspiration, forces air over the oats to blow away the loose hulls.
  • The oats are then sieved again to remove unhulled oats.
  • The remaining kernels or groats then go through polishing to remove any last bits of husk.
  • The hulls are a by-product of oat processing. They can be ground to form oat fiber and used as a filler in baking and processed meat products. They are sold as livestock feed and poultry bedding or converted to biomass fuel.


The third phase of milling is essential for stabilizing and preserving the oats, giving them a longer shelf life and preventing them from spoiling.

This step is essential as once the groats no longer have protective husks, their fatty lipids are exposed to air and will begin to break down and rot.

  • The groats enter a large steamer, where moist heat destroys harmful bacteria to prevent spoilage.
  • Another step involves exposing the wet oats to hot air. Drying and toasting them for 90 minutes to two hours develops their delicious flavor.
  • After kilning, the oats contain very little moisture, are no longer raw, and cannot sprout.
  • The oats from the kilning process are called whole oat groats and are ready for consumption.
Whole Oat Groats

Step 3: Production 

After kilning, oats enter the production stage, where the groats are prepared for different uses, depending on the size of the groat or flake needed. Production processes include cutting, flaking, and grinding.


Before production, the oat groats need sizing and separating.

This phase is required as the oat groats come in many sizes, making them suitable for different applications. In addition, oats break during milling, especially dehulling. 

The groats move over a series of sieves and screens, which separate and sort them into different sizes: 

  • Whole groat oats can be packaged to be sold as is.
  • Smaller and broken groats go for further processing.
  • Leftover, small, and badly damaged groats are an ingredient used by pet food manufacturers.


The first production procedure is called steel-cutting, where the groats get chopped up by a rotating, bladed machine.

Steel-cutting can result in coarsely cut oats (cut into only two pieces), regularly cut oats (four bits per groat), or finely cut oats.

The oats can exit production and be packaged at this stage or sent for further processing (including milling, steaming, and flaking).

Steel Cut Oats

Flour Milling

One possibility for steel-cut oats is milling them into whole-grain oat flour.

Grinding or milling takes place using stone (for stone-ground flour) or a hammer mill. 

The ground oats then pass over sieves to separate the oat bran from the flour. The oat bran is a thin, fiber-rich outer layer of the oat groat, generally hidden under the hull. Oatbran is a different product from flour and is ground and packaged for baking or making into porridge.

The remaining flour goes through mesh sifter screens to separate coarser and finer flour. The coarse flour gets ground until a fine oat flour remains.

The flour is packaged and sent to stores or used to produce infant food and baked products.


Whole groats and steel-cut oats intended for flaking first go through a steaming process to soften them and prevent breakage. Steaming also helps to further preserve and extend the shelf-life of the oats.


Flaking means that the roundish oat groats or cut oats get flattened into flakes. The larger the flake needed, the bigger groat or cut oats they will use.

  • To create oat flakes, groats get crushed between two large smooth or corrugated rollers set to the required flake size. 
  • A stream of hot air blows over the flakes to dry and further toast them.

The oats that result from the flaking process are called rolled oats and vary in flake size. Whole groats will end up 0.02 inches (0.5-0.8mm) and sold as regular, thick, or medium rolled oats. 

Steel-cut oats can be rolled into thinner flakes, going through more than one rolling. Steel-cut oats can undergo further processing through rolling and steaming to become very thin quick-cooking or instant oats.

Rolled oats can be packaged for sale or sent on to manufacturers for making into granola, muesli, snack bars, cookies, and so on. Rolled oats can be eaten “raw” at this stage or cooked into porridge.

A final stage in the journey could be seen as making oat milk by blending oats and water, read about that in my post on how to make oat milk.

Are Oats Considered Natural Or Processed?

Oats are extremely healthy but still processed because they have to go through cleaning, dehulling and kilning processes before they get to the store. Oats need processing before eating as they have an indigestible fiber hull.

However, oats are a natural product since processing involves only heat and water, with no chemical additives, coloring or flavoring agents, or sugar.

The oat processing industry focuses on making the oats edible and easier to cook by steaming, toasting, chopping, and rolling the oats into different forms.

The most “natural” form of oats is whole oat groats, which have been cleaned, the husks removed, and treated with heat. You are getting the complete oat kernel, with the healthy bran remaining.

The most processed are instant oats which are refined down to very small flakes so they cook almost instantly. These oats have the most nutrients removed from processing.

See the video for the whole journey:

Can You Eat Unprocessed Oats?

You cannot eat raw oats straight from the field. For oats to be edible, cookable, and sold in stores, they must be processed. Oat groats are the least processed and resemble the whole grain.

Processing involves cleaning, dehulling, and preserving the oats to make them safe to eat.

Unprocessed oats will make you sick, as they contain indigestible hulls and several contaminants. Even oat groats need soaking and cooking to soften them to be ready to eat.


Hopefully, you now know all about how oats are processed – without processing, oats are inedible. Oats are processed in three stages, testing, milling, and production.

Only good-quality oats will be milled, which includes cleaning, dehulling, and kilning the oats. The resulting oat groats can then enter a production phase where different products emerge: steel-cut oats, rolled oats, instant oats, or oat flour. Oat fiber and oat bran are handy by-products.

Have any questions? Ask me in the comment section below and I’ll get back to you.

Tom Hambly

Tom Hambly is the founder of Boss The Kitchen. With a background in cooking and building websites, he enjoys running this site to help other cooks improve. About Tom Hambly.

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