HOW ETHANOL IS MADE:

Dry mill production of ethanol is composed of eight steps.

The dry mill steps, described simply, are as follows:

1. Milling

The feedstock (usually corn, but can be a variety of other materials, including milo, wheat, sugar cane, beets, etc.) is passed through a hammer mill, which pulverizes it into fine particles, called meal.

2.  Liquefaction

The meal is mixed with water and an enzyme called alpha-amylase, which helps break down the meal further, into individual molecules. It is then passed through cook tanks, where the starch molecules from the meal are liquefied from the actions of  the enzyme and from heat. The cook temperature usually ranges from 250° F to 300° F. The liquefied meal is now called "mash", and is held at around 200° F, which reduces bacterial buildup while the mash is in holding.

3.  Saccharification 

The mash from the cook tanks is then cooled, and a second enzyme called gluco-amylase is added. This enzyme breaks down the starches in the mash into simpler molecules of sugars. The type of sugar created from this process is called dextrose.

4.  Fermentations

Yeast is now added to the mash to ferment the sugars. Fermentation breaks down the sugar molecules into ethanol, a liquid, and carbon dioxide, a gas.

Ethanol producers can use one of two types of fermentation processes, continual or batch. In a continuous fermentation process, the mash passes from one fermenter to another, piped together in series. By the time the mash enters the final fermenter, all the sugar will have been fermented.  In batch fermentation, the mash stays in one fermentation tank for approximately 2 days to allow complete fermentation. When the fermentation process is complete, the "mash" is now referred to as "beer." It is stored in a beer well before transfer to the next stage.

5.  Distillation 

The beer is about 10% alcohol by volume, and is not completely liquid. It also contains all the solids from the original feedstock (corn, milo, etc.) and from the added yeast. It is pumped from the beer well into a multi-column distillation system, which removes the alcohol from the beer by distillation. Basically, distillation utilizes the differences in the evaporating points of ethanol and water. Ethanol has a boiling, or evaporation, point of 178.4° F, so as long as the temperature of the columns ranges above that temperature and below 212° F, the boiling point of water, ethanol in a gaseous form, will rise to the top of the distillation column, where the gas is cooled to below 178° F. This causes the gas to condense back to liquid form, and contains a much higher percentage of ethanol than the original beer. This liquid condensate is then passed to the next distillation column in the series, where the process is repeated. By the time the product reaches the final distillation column, it is 96% ethanol, or 190 proof.

The residue from distillation, called stillage, is pumped from the bottom of these distillation columns to the co-product processing area. (See 8, below.)

6.  Dehydration 

The 190 proof ethanol is then passed through a molecular sieve, which removes remaining water that was not eliminated in distillation. Following dehydration, the ethanol is 200 proof and is referred to as anhydrous ethanol, which means "ethanol without water".

7.  Denaturation 

The Bureau of Alcohol, Tobacco, and Firearms (The ATF), requires any alcohol used for fuel be denatured, or un-drinkable. To render the ethanol unfit for human consumption, 2-5% gasoline is added to the ethanol.

8. Co-Product Processing

There are two main co-products created during the ethanol production process. The first is carbon dioxide. During fermentation, as the yeast "eat" the sugar, they not only create ethanol, but they also release large amounts of carbon dioxide gas. This gas can be captured, purified, compressed, and sold. It is used primarily in the food processing industry for carbonated beverages, and also for use in the flash-freezing of meat.

The stillage (the solids that remain after distillation) is sent through a centrifuge to remove excess liquid. This works much like the spin cycle of your washing machine. The liquid that is separated out is sent back into the process, and the remaining solids are referred to as "distillers grains". Wet distillers grains (WDG) are transferred directly from the centrifuge to a wet cake pad, where they are transferred primarily to local feedlots and dairies for use as a cattle ration. While the shelf life of this product is rather limited, several companies are marketing preservatives proven to significantly extend the product. 

Another alternative is to route the wet distillers grains through a dryer to remove most of the moisture. This dried product is appropriately called "dried distillers grains" or DDG, and is a high protein feed ingredient for cattle, swine, poultry, fish, and has been researched for human consumption. It has a significantly longer shelf life than WDG.