Our Process

Siouxland Energy Cooperative prides itself with top of the industry conversion rates. Not only are we competitive in the industry, we are achieving this while using high moisture corn. Below is a short summary of our process from start to finish.

Grain Receiving

Grain is delivered by truck to the ethanol plant where it’s loaded in a storage bin which is designed to hold enough grain to supply the plant for 4–7 days. If the corn is brought in at harvest, we crack and pack the corn and store it in a bunker, enabling us to store 25% to 50% of our annual corn needs.


The grain is screened to remove debris, and then milled into a fine powder to allow water and enzymes to contact and to react with starch in the ground material. 

Slurry Tanks

In slurry tanks, the ground material is mixed with recycled water and enzymes.  The contact and reaction of these components cause starch gelatinization, beginning the break down process of corn starch.

Jet Cooking

The slurry flows through a jet cooker, shearing the starch which allows more starch to be available for breakdown into a simple sugar, or glucose.


In liquefaction tanks, the process hydrolyzes the gelatinized starch into glucose to produce mash.


The glucoamylase enzyme breaks down the dextrins to form simple sugars. Yeast is added to convert the sugar to ethanol and carbon dioxide. The mash is then allowed to ferment for 50–60 hours, resulting in a mixture that contains about 15% ethanol as well as the solids from the grain and added yeast.


The fermented mash is pumped into a multi-column distillation system where additional heat is added. The columns utilize the differences in the boiling points of ethanol and water to boil off and separate the ethanol. By the time the product stream is ready to leave the distillation columns, it contains about 95% ethanol by volume (190-proof). The residue from this process, called stillage, contains non-fermentable solids and water and is pumped out from the bottom of the columns into the centrifuges.

Molecular Sieves

The 190-proof product stream is pumped into the molecular sieve system. These specialized tanks contain molecular sieve beads that adsorb water molecules from the process stream while ethanol molecules pass through unaffected. When the product stream leaves the molecular sieves, it contains approximately 99% ethanol by volume (200 proof).

Before the ethanol is sent to the storage tanks, a small amount of denaturant is added, making it unfit for human consumption.



The stillage from the bottom of the distillation columns contain solids from the grain and added yeast, as well as liquid from the water added during the process. This stillage is then sent and separated through the centrifuges into thin stillage (a liquid with 5-10% solids) and wet distillers grain.


The liquid that is not routed back to the cook/slurry tanks is sent through a multiple-effect evaporation system where it is concentrated into syrup containing 25-35% solids.

Oil Recovery 

We separate oil from the post-fermentation syrup stream as it leaves the evaporators. The oil is routed to oil storage tanks, and the remaining concentrated syrup is routed to both the wet distillers grain and to the syrup storage tank.