Dry milling and fractionation of grain facts for kids

Dry milling is a way to process grains, like corn, into useful products. It's like taking a whole grain and carefully breaking it apart. This process separates the grain into different parts: the germ, flour, and different sizes of grits. These parts are then used to make food for people and animals.

Dry milling is also important for making fuel like ethanol from corn. The main goal is to get the starchy part of the grain, called the endosperm, away from the germ and outer layers (pericarp). About 165 million bushels of corn are dry-milled each year.

How Dry Milling Works

Dry milling has some special features that make it unique. It separates grain parts based on their size and weight. This process doesn't use many chemicals, which is good for the environment. It also uses very little water, or sometimes none at all, for separating the parts.

This method is usually cheaper to set up than other ways of processing grain. However, it might not separate the grain parts as perfectly as other methods. This means the final products might have a slightly lower amount of starch, protein, or oil compared to other processes.

The most common machines used for grinding grains are pin mills, hammer mills, and disk mills. To get a lot of starch, grains often go through a process called degermination. This step removes the germ and the outer fiber (pericarp) first. The starchy endosperm is then collected in different sizes, like grits, cones, meal, and flour.

What Comes Out of Dry Milling?

When corn is dry-milled, it breaks down into different products. These products vary in size and how much of each you get from the original grain.

The table below shows the typical sizes and amounts of products from milled corn:

What Dry-Milled Products Are Used For?

Products from dry-milled corn are used in many different ways. They are common in animal food, for making drinks like beer, and in breakfast cereals.

Here are some common uses:

• Breakfast cereals
• Snack foods
• Pet foods
• Corn bread
• Breads
• Baby foods
• Baking mixes
• Batters
• Desserts
• Frozen foods
• Meat extenders
• Thickening agents
• Grain-based oil
• Vitamin carriers
• Mayonnaise
• Potato chips
• Soups
• Sauces
• Livestock feed

Dry milling is also great for making alcohol. It can use different types and qualities of grain without needing many changes to the machines. This makes it very flexible.

Types of Dry Grinders

There are three main ways corn is dry-milled:

• The Alkaline-cooked process
• The Stone-ground process (which doesn't remove the germ)
• The Tempering degerming process

The tempering degerming process is the most common method used in the industry today for dry-milling grains.

How the Dry Milling Process Works Step-by-Step

Dry milling corn involves several important steps. Each step uses specific equipment to achieve its goal.

Tempering

First, corn and water are mixed in a special chamber. They sit there for about 10 to 30 minutes. This step is called tempering. It helps the germ and the starchy endosperm absorb different amounts of moisture. This makes the germ more flexible and easier to separate later.

Degermination

The main goal of degermination is to break the corn kernel into its parts: the outer layer (pericarp), the endosperm, and the germ. A machine called a Beall degerminator is often used for this. It's known for getting a lot of flaking grits. This machine has a cone inside that spins very fast.

Aspiration

After degermination, aspiration is used to separate the light outer pericarp from the heavier mix of endosperm and germ. This is done by using air flow. Lighter particles are blown away, while heavier ones drop down.

Gravity Separation

Gravity separation is a method that separates things based on their weight. In dry milling, it's used to separate the endosperm from the germ. Since the endosperm and germ have different weights, gravity helps sort them out.

Roller Milling and Sifting

After separation, roller mills use spinning cylinders to grind the different materials, especially the grains. These mills can be used instead of hammer mills or ball mills. Sifting is then used to sort the endosperm particles into different sizes, like grits or flour.

Oil Recovery

Finally, oil can be recovered from the corn germ. There are two main ways to do this. One is corn expelling, which is simple and cheap but doesn't get all the oil out. The other is extraction, which gets more oil but is more expensive and has some safety risks. Extraction is used more often because it gets a higher amount of oil.