Sugar-cane vs corn ethanol

By Jillian Jastrzembski

Technically, ethanol can only be one thing: a 2-carbon alcohol with the formula CH₃CH₂OH. And yet, not all ethanol is created equal. Ethanol can be sourced, produced, and purified in multiple different ways. As it turns out, what goes on behind the scenes really does matter.

The way we produce and recycle chemicals makes a footprint on the world we live in. This footprint impacts the ecosystem, the economy, the health of the environment, and the well-being of its inhabitants.

The production process of ethanol also impacts the quality of the end product. Ethanol has multiple roles in our world, and each one requires a different chemical grade or purity. For example, fuel ethanol need not be pure or safe for consumption. But food grade ethanol must be safe and relatively flavorless, and analytical grade ethanol requires high purity.

Ethanol can be produced synthetically, but it is more commonly derived via fermentation of sugar. Ethanol produced via fermentation is called bio-ethanol. Any source of sugar will suffice, but some are more advantageous than others. The two most common sugar sources for ethanol production are corn and sugarcane.

In this article, we’re breaking down the pros and cons of sugar-cane and corn-based ethanol. Which is better for the environment? Which is better for the economy? And which is the right choice for you?

Sugar-cane ethanol

What we like about sugar-cane for making ethanol is that it’s a more efficient and eco-friendly process. Sugar-cane is made up of sucrose, which is a disaccharide composed of one glucose and one fructose. Chemically speaking, this simple sugar is a preferable starting material compared to complex carbohydrates like starch. This helps cut down on both pre-processing and purification, while resulting in fewer byproducts and a cleaner end product.

This is especially important when it comes to food grade and other non-fuel ethanol applications. As we’ll see in the next section, starch from corn needs a substantial amount of pre-processing just to create the starting material. It also produces more byproducts, so it requires extra clean-up steps.

Fermentation is the process where sugar is broken down by yeast to produce ethanol and carbon dioxide. This is the same process happening when grape sugar is fermented to produce wine. Alcoholic beverages like wine are also characterized by “secondary metabolites” or other aromatic byproducts of yeast fermentation.

As a crop, sugar-cane also holds many advantages over corn. It has better yield, crop-cycle duration, and fewer water requirements. However, in the United States, sugar-cane is not as common a crop as corn, which is why sugar-cane ethanol is often imported from countries like Brazil.

Corn Ethanol

Just like sugarcane, corn may also be used as a sugar source for ethanol production. The actual fermentation is exactly the same – yeast converts the sugar into alcohol and carbon dioxide. Therefore, both corn and sugarcane ethanol are types bio-ethanol, because they are plant-derived. What we like about corn-based ethanol is that corn is an abundantly available crop in the United States.

What’s different about corn ethanol? The sugar source in corn is not sucrose, as it is for sugar-cane. Instead, corn has starch, a complex carbohydrate. Whereas sucrose is composed of only two sugar units, starch is a polymeric carbohydrate structure with multiple sugar units connected together.

These units need to be broken up into individual glucose units in order to feed yeast for fermentation. That process is known as depolymerization.

Corn can be prepared for fermentation via wet-milling or dry-milling. Wet-milling is more energy intensive, but more effective. Dry-milling is used for fuel ethanol, which need not be as pure. However, all non-fuel ethanol, including food grade ethanol, must undergo wet-milling to extract the starch from other components of the grain. Eliminating those non-starch components from the starting material is important, because it helps to eliminate byproducts of the fermentation.

And yet, fermenting wet-milled starch still produces a messier end product compared to sugar-cane ethanol. Byproducts of starch fermentation include short chain fatty acids, esters, and aldehydes, which contribute to undesirable off-aromas. These need to be removed for most non-fuel applications of ethanol. Other byproducts are considered safety concerns, including compounds like phenol, benzoic acid, and styrene. These too must be removed to create food safe or high-purity products.

Corn ethanol is therefore more challenging to purify, following fermentation. Distillation can be used as a first step, but because water and ethanol form an azeotropic mixture, the highest purity that can be achieved from distillation is 96.5%. Besides, other organic impurities will not necessarily be removed during distillation. Other methods must be used, such as the use of adsorbent materials, including activated carbon.

Are corn ethanol and sugar-cane ethanol vegan and Kosher?

One advantage of both corn and sugar-cane ethanol is that it is relatively easy to comply with Kosher law. This is not the case for all bio-ethanol. For example, it is also possible to produce ethanol from lactose, a sugar found in dairy. Lactose-derived ethanol would not be considered Kosher. Any ethanol must also undergo the official process for Kosher certification.

It is certainly possible to keep bio-ethanol vegan. However, one consideration is that bone char is often used in the production of sugar from sugar-cane. Bone char is made by charring animal bones, typically from pigs or cows. It is possible to replace bone char with activated carbon (from a non-animal source), in order to produce a vegan product. The product must still undergo the official USDA certification to obtain the vegan label.

Corn ethanol or sugar-cane ethanol: which is better?

All things considered, which is a better source for ethanol: corn or sugar-cane? Corn is America’s most abundant crop, making it the obvious domestic choice. Meanwhile, sugar-cane ethanol is by far the more efficient and eco-friendly option.

References

Onuki, Shinnosuke, et al. “Taking ethanol quality beyond fuel grade: A review.” Journal of the Institute of Brewing 122.4 (2016): 588-598.

Price, Rabbi Gavriel. “Kosher certification of nutraceuticals and dietary supplements.” Nutraceutical and Functional Food Regulations in the United States and around the World. Academic Press, 2019. 601-607.

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