Target Grade Level / Age Range:
High School: 9-12
As a result of this lesson, the student will …
- Identify the types of fermentation that can produce ethanol.
- Identify how starch and cellulose differ in the fermentation process..
- 8 ½ x 11 or larger paper
Suggested Companion Resources
- Cellulose – a long chain of linked sugar molecules that give wood and other plant matter its strength. It is the main component of plant cell walls
- Cellulosic ethanol - biofuel produced from wood, grasses, or the inedible parts of plants
- Starch – carbohydrate consisting of large glucose (sugar) units joined together
- Enzyme – biological molecules (proteins) that act as catalysts and help complex reactions occur. Specific enzymes are required to catalyze different reactions.
- Distillation – the act of purifying a liquid by a process of heating and cooling
- Milling – to grind or crush corn or other grains.
- Dry-milling – a less versatile, less capital intensive process of milling corn for ethanol production that primarily focuses on the production of grain ethanol
- Wet-Milling – feed material is steeped in water to soften the seed kernel to separate the various components. By-products can be removed and repurposed before the starch is used to produce ethanol
- Liquefaction – a process that generates a liquid from a solid or gas
- Saccharification – the process of breaking a complex carbohydrate (like starch) into simple sugars
- Fermentation – metabolic process that converts sugar to alcohol
- Distillation – action of purifying a liquid by a process of heating and cooling
- Dehydration – the process of removing water from a substance or compound
- Denaturing – to render unfit to eat or drink without destroying usefulness in other applications
- Germ – reproductive part (embryo) of the seed that will grow into a plant
- Fiber – plant material that cannot be easily digested in monogastric animals
- High fructose corn syrup – sweetener (also called glucose-fructose) made from corn starch.
Background – Agricultural Connections
Before teaching this lesson, the instructor should first review how to correctly balance chemical equations.
Interest Approach or Motivator
Recall with students that ethanol is a product of fermentation, highlight the following points:
- Ethanol is a product of fermentation.
- Define fermentation as a sequence reaction which releases energy from organic molecules in the absence of oxygen.
- Sugar converts to Ethanol + Carbon Dioxide
Explain to students that all beverage ethanol (alcohol) and industrial ethanol (fuel) is made in this process. Lead students to this understanding by making comparisons of other items that are similar, but carry differences. For example, apples and oranges are both fruits and both are grown on trees. Both can be eaten with little preparation. But, you might only use apples to make a pie. Go on to explain that all ethanol is not made through the same process. In objective 1, students will write down the fermentation equation and explain the two methods used in the production of ethanol.
Now think about raw milk. What is raw milk used to make? Elicit student responses.
Raw milk is used to make a number of different products including the milk we drink, cream, cottage cheese, yogurt, ice cream, buttermilk, and is processed a number of different ways to be used in hundreds of foods. Ethanol also has similarities and differences. We are mostly concerned with industrial ethanol, or ethanol that is made for use as a fuel. Food grade ethanol can also be produced. While the outcome is a little different and the products are used for different reasons, the process of fermentation is virtually the same. Sugars are broken down to make ethanol and a by-product of carbon dioxide. There are, however, a couple of different fermentation processes depending on what the raw material is. Today we will examine the fermentation equation in-depth. We will be able to identify and describe two different fermentation processes.
OBJECTIVE 1. Identify the types of fermentation that can produce ethanol.
- Fermentation Equation: Raw Material + Yeast= Ethanol (Energy) + by-product of carbon dioxide. C6H12O6 -> 2 CH3CH2OH + 2 CO2.
The fermentation processes yields two products. Ask students to name the two products (ethanol and carbon dioxide).
Ask students to recall the input in the fermentation process (sugar).
As students write the chemical equation have them assign a color for each component. The instructor should record the equation on the board using colored writing utensils to match the suggestions in the lesson.
Students can choose any color crayon and write “Fermentation Equation” as a heading in their notes. Then locate brown, red, blue and at least one other color crayons/markers. We know that sugar is an input to the fermentation equation. Since this sugar or simple carbohydrate hasn’t been processed yet, call it a “Raw Material” for our equation. The brown crayon will represent the inputs to our equation. Use the brown crayon to write “Raw Material” on the far left side of the equation.
We also need yeast in this equation on the left side of the equation. Using a color other than brown, red or blue, make a plus sign to the right of raw material. Now, write “Yeast” to the right of the plus sign using the brown crayon.
Raw Material + Yeast
These two components yield, or equal two outputs, ethanol and carbon dioxide. Use the number/symbol crayon and draw an equal sign in the equation to the right of yeast.
Raw Material + Yeast =
Locate the red and blue crayons. These represent the outputs of our equation. Use the red crayon to write ethanol and the blue crayon to write carbon dioxide, so our equation should look like what I have on the writing surface.
Raw Material + Yeast = Ethanol + Carbon dioxide
Now guide students through the process of writing the chemical equation for the fermentation process using elemental symbols. Using the corresponding colors for the elements, write the equation, and then explain how the equation is similar to the equation above that is written out in words.
There will be three elements in our equation that will make up the components. They are C – carbon, H – hydrogen, and O – oxygen. Use the same colors to match up with our previous equation.
The first part of our equation is C6H12O6. This represents the raw material, or sugar and yeast. Use brown again to write out this compound. (Note: yeast is a living organism and can’t be represented as a single chemical compound.)
Next, draw a symbol that leads to the right side of the equation, or the products. Use an arrow, this arrow means “equals” or “yields”. Using the crayon you chose for numbers and symbols draw an arrow left to right from the chemical compound we just drew.
Since we used the elements carbon, hydrogen and oxygen on the left side of the equation, we need to see those same elements on the right side of the equation. Ask students what can be expected on the right side of the equation, or what are the products of this process?
We should see the results of ethanol and carbon dioxide. Write these compounds in a chemical equation. Leave some space between the arrow and the placement of your next letter. The compound we want to get out of this process is ethanol.
C6H12O6 => CH3CH2OH
The second product of the fermentation process or a by-product is carbon dioxide. What is the chemical compound used to represent carbon dioxide? (One atom of carbon and two atoms of oxygen). Use blue to represent carbon dioxide and record that compound.
C6H12O6 => CH3CH2OH + CO2
In order to balance this equation, we need to make sure there is the same number of atoms of each element on each side of the equation. To balance the equation, we must add a 2 before ethanol and carbon dioxide to get the same amount of atoms on the right side. Let’s do that now. (Instructors may wish to go in-depth into teaching balancing equations; this is suggested below as an extended classroom activity.)
C6H12O6 => 2 CH3CH2OH + 2 CO2
As we look at the two equations we wrote, we can immediately see the similarities because of the color coding. Brown represents the inputs sugar and yeast. What does red represent? (ethanol) And blue represents oxygen. As you think back to the fermentation process, you can make associations with the colors and the compounds involved.
- There are different types of fermentation processes that are used depending on what the raw input ingredient is.
- Typically ethanol is derived from grains such as corn and wheat in which starch is readily available and easily broken down into sugars.
- Cellulosic Ethanol- ethanol that is exactly the same as grain-based ethanol, but it is made from agricultural residues (wood, corn stover, grasses, etc.).
OBJECTIVE 2. Identify how starch and cellulose differ in the fermentation process.
The starch and cellulose fermentation process each have unique steps.
- Starch Dry-milling Process
- Starch must first be broken down into simple sugars before fermentation can even occur.
- Milling: Corn, barley or wheat is cleaned and then passed through hammer mills to break the exterior hull and grind it into fine powder.
- Liquefaction: The meal will then be mixed with water and an enzyme called alphaamylase as a catalyst.
- The meal will pass through cookers where the starch is liquefied.
- A pH of 7 is maintained by adding sulfuric acid or sodium hydroxide.
- Heat is applied to enable liquefaction.
- Cookers with a high temperature stage 120-150 degrees Celsius and lower holding period of 95oC will be used.
- The higher temperature reduces the bacteria in the mash.
- Saccharification: The mash from the cookers will be cooled and the enzyme glucoamylase will be added to convert starch molecules to fermentable sugars or dextrose.
- Fermentation: Yeast will be added to the mash to ferment the sugars to ethanol and carbon dioxide. Fermenting mash will flow through several fermenters until the mash is fully fermented and leaves the tank. In a batch fermentation process the mash stays in one fermenter for about 48 hours.
- Distillation: The fermented mash will then be pumped to the continuous flow, multicolumn distillation system where the 10% alcohol will be removed from the solids and 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 coproduct processing area.
- Dehydration: The alcohol will then pass through the dehydration system where the remaining water will be removed. Most plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol at this stage is call anhydrous.
- Denaturing: Ethanol that will be used for fuel is then denatured with a small amount (5%) of some product like gasoline, to make it unfit for human consumption
- Starch Wet-Mill Process: by products are removed throughout the cycle instead of only at the end
- Cleaned and inspected corn is steeped (soaked) for up to two days, which begins to break down the bonds holding the starch and proteins together.
- The corn is then coarsely ground up to remove the germ from the rest of the components. The germ can be used to make corn oil, and the remainder of that process creates some feed products that can be given to livestock.
- The slurry is finely ground. The fiber is then taken out using an attrition-impact mill. The fiber is used as an element in animal feeds.
- The starch and gluten are separated using a centrifuge to make the denser starch fall to the bottom of the mix. The starch continues in the process towards becoming ethanol. Gluten is used as another ingredient in animal feeds.
- Water and enzymes are added that will ferment the starches into ethanol and other alcohols. Some of the unused starch is removed to be turned into high fructose corn syrup, a common inexpensive sweetener.
- During fermentation, the CO2 gas that has collected in the fermentation chamber is removed and sold to soda companies for carbonation.
- Cellulose Production Process
- Made from cellulosic biomass materials that are composed of cellulose, hemicellulose, and lignin.
- Plant wastes- corn stover, cereal straws, sugarcane and bagasse
- Plant wastes from industrial processes- sawdust, paper pulp
- Energy crops- switch grass.
- Aim is to extract fermentable sugars from the feedstock, in which they are locked in complex carbohydrates called polysaccharides.
- Separating complex structures is essential to the efficient and economic production of cellulosic ethanol.
- There are two major processes in cellulosic ethanol production
- Acid hydrolysis- this is the break-down of complex carbohydrates to simple sugars.
- Enzymatic hydrolysis- this process utilizes pre-treatment process to reduce the size of the material to make it accessible for hydrolysis. Enzymes then are added back in to break corn material for fermentation.
- Made from cellulosic biomass materials that are composed of cellulose, hemicellulose, and lignin.
Students will create map of the process organizing the various steps in the ethanol production process. Prior to class, cut out the Tassel to Tank information slips and randomize them. With the background knowledge they now have, students should be able to work together and organize the steps of the ethanol process.
Divide students into 13 groups (pairs or trios). Distribute one random Tassel to Tank information slip to each group. Give students 5-8 minutes to familiarize themselves with the information on the card and answer the card’s discussion question(s).
One at a time, have a leader from each group come to the front of the class and present the information about their production step. Then, ask the student to place their step in the correct order, relative to the other steps already standing at the front of the class.
Review the information with students and discuss the tougher questions from the Tassel to Tank information slips. Display the two slides mapping out the ethanol process. Discuss at what point in the process the enzymatic reactions happen (pretreatment, hydrolysis, fermentation). Discuss at what point in the process the sugars are converted to ethanol (fermentation).
Have students in pairs or as individuals recreate the maps in their notebooks. Using their own words to describe what happens at each stage, have students write a short story about a character (Kernel Corn, Biomass Betty, or another of their choosing) as he/she travels through the process. Students can choose to write a story about either the starch based process or the biomass based process. Have students explain what happens to their character at each stage. Allow student creativity – for example using a hammer to crush the grain. Give students 5-8 minutes to write their stories.
The instructor should circulate through the room to be sure individuals or groups are including essential elements in their stories and to assist groups in creating describing what is happening.
Review the ethanol and fermentation process by allowing students to share their stories. As students are sharing, the instructor should correct any technical inaccuracies.
Answers to Evaluation:
- Acid hydrolysis
- Enzymatic Hydrolysis
- 2 Liquefaction
- 4 Fermentation
- 1 Milling
- 6 Dehydration
- 3 Saccharification
- 5 Distillation
- 7 Denaturing
- C6H12O6 -> 2 CH3CH2OH + 2 CO2.
- The starch process breaks down carbohydrates at a more rapid pace than cellulosic fermentation. Starch fermentation is cheaper and more economical than cellulosic.
- The major difference in the wet mill and dry mill process is that in the wet mill process after milling, the corn is heated in a solution of water and sulfur dioxide for 24-48 hours to loosen the germ and hull fiber. The germ is then removed from the kernel and corn oil extracted from the germ. The remaining germ meal is added to the hulls and fiber to form corn gluten feed. The only fermentation that occurs in wet-mill processing is that of the germ while the entire seed is used in dry-mill processing.
- Corn gluten meal, corn gluten feed, also used as animal feed, corn germ meal, corn oil, carbon dioxide, and high fructose corn syrups.
Essential Files (maps, charts, pictures, or documents)
Did you know? (Ag facts)
- The fermentation process to convert corn into ethanol takes between 40 and 50 hours.
- Instructors can teach a “lesson within the lesson” on balancing chemical equations and go in depth on why twos were placed before ethanol and carbon dioxide in the chemical equation for fermentation. Additionally, instructors can obtain chemical equations for other reactionary processes to allow students to practice balancing chemical equations.
- Invite a chemist (preferably involved in the ethanol/fermentation process) to serve as guest speaker for career exploration opportunities.
- Any students involved in grain production can give a short talk on the production process from planting to harvest so students can see where the raw material in the fermentation process originates.
- Adapted from Renewable Fuels Instructional Materials: Copyright © 2009 by National FFA Organization. Used by permission.
- E-Moments® is a registered trademark of the National FFA Organization. Copyright © 2004 by National FFA Organization. Used by permission.
- New materials, updates and revisions were funded in part by a grant from the Iowa Energy Center as a special project of the Iowa Agriculture Literacy Foundation.
Iowa Agriculture Literacy Foundation
Agriculture Literacy Outcomes
- Theme 4: STEM
- Identify current and emerging scientific discoveries and technologies and their possible use in agriculture (e.g., biotechnology, bio-chemical, mechanical, etc.)
- Evaluate the benefits and concerns related to the application of technology to agricultural systems (e.g., biotechnology)
Education Content Standards
- HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
- HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
Common Core Connections
- NL-ENG.K-12.6. Applying knowledge.
- W.9–10.2 Write informative/explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately through the effective selection, organization, and analysis of content
- W.9–10.3 Write narratives to develop real or imagined experiences or events using effective technique, well–chosen details, and well–structured event sequences.