Title:



Title: Coffee: It’s in the Roast!

Grade: High School

Length: 40 minutes

Purpose: To discover what is occurring at a chemical level when roasting coffee beans.

Learning Objectives:

• To understand the chemical reactions happening when roasting coffee.

• To realize that one can experiment roasting coffee at home with simple equipment.

• To understand that timing is the key element in determining the resulting roasts (light, medium, dark).

Introduce Ourselves (1 minute)

Introduction (5 minutes): The Legend of Coffee:

Cue: Divide classroom into three different tables before students enter the classroom so that groups are already made. Have Dixie cups set out with each of the three types of beans in them, three popcorn poppers, bowls, colanders, oven mitts, and all supplies set out on the table. Each table will have its own supplies.

►Legends of Coffee Slide

• Does anyone know what the world’s largest commodity is? (Pause)

• It’s oil. How about the second largest commodity? (Pause) Some would be surprised that coffee is the world’s second largest commodity.

• So how has this come about? How was coffee even founded in the first place? One legend says that coffee was first harvested by a goat-herder who noticed that his herd became friskier than usual after consuming the red cherries of a wild coffee shrub. Curious, he tasted the fruit himself. He was delighted by its invigorating effects, and was even spotted by a group of nearby monks dancing with his goats. Soon the monks began to boil the bean themselves and use the liquid to stay awake during all-night ceremonies.

►Cherries on the Branches Slide

• Another legend says coffee was actually called mocha. It was discovered in Arabia by a man named Omar. Omar who was banished in the desert with all his followers. There were put out there to die of starvation. As an act of desperation, Omar made one of his friends collect fruit from an unknown plant and boiled them to prepare a meal. This meal not only saved the entire party but also its survival gave a religious significance to the nearest town that went by the name of mocha where they settled. After this event, the plant was called mocha.

• Clearly coffee was a food before it was a drink. In fact, warriors around the time of 1000 A.D. crushed up coffee beans, mixed it with animal fat and rolled them into bite size balls. This was used to keep warriors from fatiguing or tiring during a battle.

• So why don’t we take a look at what coffee looks like before and after the coffee bean is roasted. In front of you are three different types of beans. The green ones are green coffee beans that have not been roasted, the brown ones are green beans that have been roasted, and the other ones are chocolate covered coffee beans. If you’d like, you are welcomed to try the roasted coffee bean, but probably not the green ones because they are very hard. If you aren’t very brave, go ahead and try the chocolate covered coffee beans.

• So what makes a green bean different than a roasted bean?

• How do you roast a bean and turn it into what we know as coffee? In this exercise, we will explain the origins of coffee, the chemical reactions and process of roasting the bean, and the elements of how one green coffee bean can turn into a full-bodied cup of coffee. With this knowledge, each of you will get to roast your own coffee.

• The National Coffee Association reported in 2003 that 166 million people drank coffee, with 37% of them being between 18-24 years of age. Franki is going to go more in depth about the chemical reactions happening when roasting coffee, the chemicals involved, and the exact balance it takes to roast a full-bodied cup of coffee.

Lecture (10 Minutes): Chemistry of Coffee Roasting

►Coffee Orchard Slide

Today we will experiment roasting coffee beans together. But first, we’ll talk about what actually happens to the green coffee beans during the roasting process. We’ve heard a few fun stories about how and when coffee was discovered, from eating the actual cherries, to boiling the green beans in water and grinding them into foods….those stories date from the 6th to the 10th centuries. But it wasn’t until many years later that it was discovered that roasting the green beans was the optimal means by which coffee could and would be best appreciated.

►“Map of Coffee World Slide

In 1475 the world’s first coffee shop opened in Constantinople, and it wasn’t until almost 400 years after that, in 1822, that the prototype of the first espresso machine was created in France.

In any good basic cooking class, you will learn that chemistry is the key element from which combinations of ingredients and order are defined. Understanding which ingredients work (or don’t work) together will change the way you approach cooking for the rest of your life. For example, salt melts in vinegar; therefore when you make your salad dressing you will always mix the salt with the vinegar before you add the oil. If you don’t, the salt remains in crystal form.

Transition: It is no different when “roasting” green coffee beans. In fact, scientists continue to learn more each day about the intricacies involved in roasting coffee. But, what do we know to date?

Many thermal and chemical reactions occur during the roasting process. Each of the following three major components of the green coffee bean reacts at a different temperature which is why careful temperature calculation, measurement and monitoring is so important during roasting. We will talk mainly about Sucrose, Cellulose and Trigonelline.

►Sucrose Definition Slide

Lacy will be posting the formal definitions and their formulas as I speak, but I’ll let you read them yourselves. Let us know if we move through them too quickly.

Sucrose – Sucrose is the principal sugar in coffee…..it’s the energy in the bean.

The melting point of pure crystalline sucrose is in the 160C -200C range, with 188C being the most commonly accepted temperature. To give you a frame of reference, water boils at 100C or 212F. And you bake a cake or a pie at about 188C or 370F.

►First Table Slide

Between 170C and 200C carmelization begins. It is at this time that water and carbon dioxide fracture and out-gassing begins, which causes the “first pop” of the bean. [When I say “first pop” I actually mean an audible pop. You can hear the bean pop, almost like popcorn. And you will hear the popping yourselves in a moment.]

The hotter the temperature, the more sucrose is carmelized and less amounts of sugar (or sweetness) remain. Carmelized sugar is less sweet in the cup than non-carmelized sugar.

So the darker the roast - the longer it’s been in the roaster, the more carmelized the sugar is, and the less sweet it is. The shorter time in the roaster, the less carmelized the sugar is, and the more sweet it is. Lacy put up a table for you which charts these temperatures and reactions in a concise manner. Franki…. pause here.

►Cellulose Definition Slide

Cellulose – Cellulose is the principal fiber of the cell walls of the coffee cells. It is the actual structure of the green coffee bean. Like wood is to the frame a house, cellulose is to the coffee bean.

►Second Table Slide

Darker roasts must reach the temperature which will cause a “second pop.” The beans must continue to be heated after the first pop, to over 230C to break or “fracture” the cell walls. Roasters and scientists have discovered that by limiting the maximum temperature to 271C, the damage to the cell is also minimized; and this enhances the overall “cup” complexity.

So what do you think would happen if you keep increasing the temperature? Yes, the coffee beans will burn.

Lacy put up the same table for you but this time, the cellulose component is included. Franki, pause again.

►Trigonelline Definition Slide

Trigonelline – Trig-o-nel-line is a nitrogenous base in coffee which is 100% soluble in water. It is the most significant component contributing to excessive bitterness. In a higher temperature roast (a darker roast), a roast reaching the second pop, ~85% of the trigonelline will be degraded or removed.

►Third Table Slide

So you can see that if the bean does not reach the second pop stage, it will contain more trigonelline. Lighter roasts will have more trigonelline. Does this mean that the beans with more trigonelline will be more bitter? Well possibly. But remember what we just learned about sucrose….that the less you roast a bean, the less the sucrose is carmelized and the sweeter the result.

This is why when the beans are properly roasted, the two elements (sucrose carmelization and trigonelline removal) can form an interesting compliment to each other. Notice the different possibilities in just these three components. Franki, look at the slide.

►Balance Slide

You can see that balance is very important, balancing the temperature so that the ideal amount carmelization is married with the proper degradation of the trigonelline, for example.

But there are other chemical elements that affect the roasting results. There are many other acids and aromatic oils that change the flavor and aroma of the coffee as well as the 3 primary components we’ve reviewed today.

So you can see that there are many combinations possible which give the roaster the freedom to develop his/her own style and roast. In addition, the roaster must also keep in mind the density of the bean which will vary depending on the country where the coffee is grown and the altitude and location of the orchard.

►Separating Cherries/Washing/Roasting/Cooling Slide

Let’s look at the 4 pictures on this slide behind me, starting with the one at the bottom right and moving counter clockwise. Washing & separating the cherries from the beans, washing the green beans, roasting the beans and cooling the beans.

Transition:

I can tell that you are all Expert Coffee Roaster Wannabees right now. So, I think it is right and just that you can all put your newly attained knowledge to the test. Tara will lead you through an activity which will give you some hands on expertise in roasting beans that you will be able to take home to practice on your families.

Activity (22 minutes): Popcorn Popper Roasting

Today we are going to roast coffee beans in air pop popcorn poppers. As we have all just learned through lecture, the ultimate taste of the coffee depends on the temperature the beans reached during roasting. For our experiment, temperature will be determined by the length of time the beans are in the popcorn popper; with the longest time reaching the highest temperatures. In general, to obtain a light roast through a popcorn popper, we would roast the beans for around 4 ½ minutes. To obtain a dark roast the beans would stay in the popper for approximately 7 minutes. A medium roast starts around 5-6 minutes.

This group has a medium-light roast, which are Ethiopian beans. This group has a medium roast beans, which are Peruvian beans. This group has a dark roast, which are Sumatran beans.

Each group has a bean whose optimal roast is light, medium or dark, and as a group you will decide how long you want to roast your bean.

• We are working with very hot beans please be very careful not to burn yourself or any of your classmates. We have water and fire extinguishers available in case anything should get out of hand.

• As we discussed, in order to bring out the best taste in any given bean, each bean has an optimal roasting time. As a group you should now determine how long you want to roast your bean. Remember, for a light roast we would want to roast for around 4 minutes, for a medium roast, about 5-6 minuets and for a dark roast about 7 minutes.

• Now that we have each decided how long to roast, we will place these large bowls in front of the popcorn poppers air chute to collect the chaff that comes off of the beans. Chaff is a fine skin like part of the bean that comes off during roasting.

• Each group has a colander (or strainer) and a large wooden spoon. For the time being, we will have these on our work surface and will use them later.

• Now, each group needs to designate one member to wear the oven mitts. This person will handle the poppers lid once the machine has been turned on. We will only be using one scoop of beans per group. Please use the measure cup that is part of your poppers lid to measure the correct amount of beans. Set these aside for now.

• Ok, now the fun starts. Lets all plug in our hot air popcorn popper machine and let it warm up for 30 seconds

• Set your timers for your groups predetermined roasting time. As one member starts the timer, another should quickly pour your beans from the lid measure cup into the machine. You should see your beans just barely rotating.

• One member should now take the wooden spoon and stir the beans.

• The student with the oven mitts will now place the lid back on the popper. The beans are now roasting. You can observe the process though the lid.

o Note the beans will still be green with only a small sweet smell

o At 2.5 minutes, the chaff should start shooting into the bowl

o Note the sweet smell

o At 4 minutes in, note the crackling sound known at the first crack

o This is the start of a light roast

o Note the light brown color

o At 5 to 6 minutes, a higher pitch crackling begins (second crack)

o This is the start of a medium roast

o Note the medium to light brown color

• Once your group has reached your desired roasting time, unplug your machine.

• The student with the oven gloves should quickly pour your beans out of the popper into your colander.

o DO NOT FOR ANY REASON TOUCH THE BEANS

• Take the colander over to the designated garbage bin and sift the beans to cool and remove any chaff that is remaining.

o DO NOT FOR ANY REASON TOUCH THE BEANS

• After a 10 minute cooling period, your beans should be cool enough to touch and taste.

• Once the other group’s beans have cooled, you may want to taste the beans. You should be able to observe a difference in each of the roasts.

• Now if your group has time, you may roast another batch of beans! This way if you felt you burned your beans, you can experiment to find a better roasting time.

• Clean up

Conclusion (1 minute): Although the goat herders hundreds of years ago did not have popcorn poppers and chocolate covered coffee beans, they were able to enjoy the stimulating affects of coffee beans just as we do today. And although we are not going into battle hyped up on caffeine from ground up coffee beans and animal fat, sometimes our mornings do feel that way.

• We have some coffee that we have been brewing from these same beans. If you would like to take a taste, please feel free to grab a small cup. Enjoy!

Supplies:

• 3 popcorn popper machines

• 3 Large Bowls

• 3 Long Wooden Spoons to handle and stir the hot beans

• 3 Colander’s for roasted beans

• Oven Mitts

• 3 Jugs of Water

• 3 types of green coffee beans

• Same 3 types of already roasted beans (just in case)

• Bowls (other) to store roasted beans

• 3 Kitchen timers

• 3 cue cards designating light, medium, dark station along with the name of the coffee bean

• Chocolate covered beans

• Computer for PowerPoint

• Note cards

• Drip coffee maker

• Filters

• Previously ground coffee beans

• Four ounce hot coffee cups

• Half and half

• Brown sugar

Resources:

1. Starbuck describes the history of coffee and the legends that surround it.

ourcoffees/coffee

2. Discussion on the history of coffee retrieved on January 18, 2009 at coffee.

3. The National Coffee Association goes over the history, roasting, and brewing of coffee. 2009.

4. Straub, Carl. (1995). Basic Chemical Reactions Occurring in the Roasting Process. SCAA (Specialty Coffee Association of America) Roast Color Classification System. Retrieved January 18, 2009 from .

5. Basic Chemical Reactions Occurring in the Roasting Process sourced from the SCAA and summarized. Retrieved January 18, 2009 from .

6. Coffee Chemistry: Acidity, Aroma and Cause of Bitterness. Retrieved January 18, 2009 from .

7. The coffee roasting process. How coffee roasting enhances the smell and taste of coffee beans

8. Coffee Geek. Tips on roasting in a popcorn popper.



9. How Coffee Roasting Enhances the Smell and Taste of Coffee:

Time for Coffee and Tea The Coffee Roasting Process. 2009. Time for Coffee and Tea 22nd January 2009.

10. The various stages of Coffee Roasting:

The Ins and Outs of Coffee Bean Roasting. 2008. Café – Shrewd Operations. 22nd January 2009.

11. Home Coffee Roasting Activity:

Discover the World of the Home Coffee Roaster. 2006. Gourmet-Coffee-Lovers-. 22nd January 2009.

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