1. Milling: The
corn (or barley or wheat) will first pass through hammer mills, which grind it
into a fine powder called meal.
2. Liquefaction:
The meal will then be mixed with water and alpha-amylase, and will pass through
cookers where the starch is liquefied. Heat will be applied at this stage to
enable liquefaction. Cookers with a high temperature stage (120-150 degrees
Celsius) and a lower Temperature-holding period (95 degrees Celsius) will be
used. These high temperatures reduce bacteria levels in the mash.
3.
Saccharification: The mash from the cookers will then be cooled and the
secondary enzyme (gluco-amylase) will be added to convert the liquefied starch
to fermentable sugars (dextrose), a process called saccharification.
4. Fermentation:
Yeast will then be added to the mash to ferment the sugars to ethanol and carbon
dioxide. Using a continuous process, the fermenting mash will be allowed to
flow, or cascade, through several fermenters until the mash is fully fermented
and then leaves the final tank. In a batch fermentation process, the mash stays
in one fermenter for about 48 hours before the distillation process is started.
5. Distillation:
The fermented mash, now called "beer," will contain about 10% alcohol, as well
as all the non-fermentable solids from the corn and the yeast cells. The mash
will then be pumped to the continuous flow, multi-column distillation system
where the alcohol will be removed from the solids and the water. The alcohol
will leave the top of the final column at about 96% strength, and the residue
mash, called stillage, will be transferred from the base of the column to the
co-product processing area.
6. Dehydration:
The alcohol from the top of the column will then pass through a dehydration
system where the remaining water will be removed. Most ethanol plants use a
molecular sieve to capture the last bit of water in the ethanol. The alcohol
product at this stage is called anhydrous (pure, without water) ethanol and is
approximately 200 proof.
7. Denaturing:
Ethanol that will be used for fuel is then denatured with a small amount (2-5%)
of some product, like gasoline, to make it unfit for human consumption.
8. Co-Products:
There are two main co-products created in the production of ethanol: carbon
dioxide and distillers grain. Carbon dioxide is given off in great quantities
during fermentation and many ethanol plants collect that carbon dioxide, clean
it of any residual alcohol, compress it and sell it for use to carbonate
beverages or in the flash freezing of meat. Distillers grains, wet and dried,
are high in protein and other nutrients and are a highly valued livestock feed
ingredient. Some ethanol plants also create a "syrup" containing some of the
solids that can be a separate production sold in addition to the distiller's
grain, or combined with it. Ethanol production is a no-waste process that adds
value to the corn by converting it into more valuable products.
Ethanol is also
made from a wet-milling process. Many of the larger ethanol producers use this
process, which also yields many other products, such as high fructose corn
sweetner.
Grain
Ethanol