What Affects the Caffeine Content of Coffee?

Many people rely on the caffeine in coffee to give them a jumpstart in the morning and keep them going throughout the day. In fact, the International Coffee Organization (ICO) has reported Americans alone consume 400 million cups per day. This makes up 45% of daily worldwide coffee consumption. It makes you wonder how much caffeine is in that much coffee.

The Food and Drug Administration (FDA) estimated that a typical 8-ounce cup of coffee includes 80-100 milligrams of caffeine. Doing the math, we see the large amount of caffeine Americans consume daily through coffee alone.

What is Caffeine?

Natural caffeine is a substance that occurs in plants such as coffee beans, tea leaves, and cacao pods. It stimulates the central nervous system and brain to wake people and keep them alert. Caffeine is also produced synthetically for use in products such as sodas and energy drinks.

What Are Other Ways Caffeine Can Affect Our Bodies?

Along with the energy boost it provides, most coffee drinkers enjoy the taste of freshly brewed coffee. As you reach for the second (or third) cup of coffee of the day, it is important to understand the effects that caffeine has on your body.

What can happen if you consume too much caffeine?

Overconsumption of caffeine can have effects on your body over time. These effects can include heartburn, elevated blood pressure, decreased bone density, and muscle twitching. With continued caffeine consumption, your body may go through withdrawal if caffeine is discontinued. Withdrawal symptoms can include headaches, dizziness, anxiety, and irritability.

Studies have also shown that caffeine, in moderation, can have positive effects. For regular coffee drinkers, these include a decreased risk of developing Alzheimer’s and dementia, certain cancers, strokes, Parkinson’s, and decreased suicide risk (by 45%). On a daily level, studies have shown caffeine can boost concentration and memory levels.

What are the Factors Affecting Caffeine Content in Coffee?

Because we know caffeine can have both negative and positive effects on the body, it would be helpful to understand the factors affecting the caffeine content in your next cup of coffee. Monitoring the caffeine content in your coffee prevents overconsumption of the stimulant and the negative side effects associated with it.

1. Coffee Beans – Arabica or Robusta?

If you brew your coffee using Arabica beans, you may find taste or cost to be more important than the caffeine content of your coffee. Arabica beans are known for their sweet fruity taste and high acidity. They also have about half the caffeine content of Robusta beans. Because they are easier to grow, Robusta beans are lower in price but tend to have a bitter taste.

2. Type of Roast – Light or Dark?

In general, the myth of dark roast beans having a higher caffeine content relative to light roast beans has been debunked. It is not about the roasted beans themselves, but the grinds used to make the coffee.

A study looking at the correlation between roast levels and caffeine content found the answer to be less than straightforward. It is important to understand that roasting time in itself does not directly affect the caffeine content of coffee beans. However, roasting time affects the mass of the beans.

How does the change in the beans’ mass affect the caffeine content of the coffee?

If you measure out your coffee grinds using a scale, then the study found there was a noticeable difference (+32%) in the caffeine content of coffee brewed with dark roast beans versus light roast beans. Because longer roasting times result in beans with lower density, more of them are required to reach a certain weight. 

However, most coffee drinkers opt to measure out their coffee grinds using a scoop or spoon. In this case, the difference in the brewed coffee’s caffeine content was found to be only 9% more with dark roast beans. During the roasting process, the beans’ density has changed, but not so much the coffee beans’ size. Read about the science behind the roasting process to understand what happens to the coffee beans.

3. Brewing Methods

In general, coffee brewing methods with a higher level of extraction will produce coffee with higher caffeine content. Dr. Bob Arnot, the author of The Coffee Lover’s Bible, outlines the following brewing factors affecting your coffee’s caffeine content:

  1. Grind size: Brewing coffee beans with a smaller grind size will produce coffee with higher caffeine content. This is due to the greater total surface area (relative to volume) of the smaller grinds.
  2. Water temperature: Brewing with hotter water extracts more caffeine from coffee grinds. 
  3. Brewing methods: Methods that fully immerse the coffee grinds produce coffee with higher caffeine content relative to pour-over methods. Full immersion brewing methods also allow the grinds to brew longer if desired. With longer brewing times, more caffeine is extracted from the grinds.

For maximum extraction during brewing, coffee drinkers should discover the optimal balance between these factors. However, keep in mind that specific brewing methods require a certain grind size and water temperature.

The Science of Coffee Roasting

coffee brewing in chemex pots
coffee bean berries

Coffee comes from the seeds of the fruit of the coffee tree, but the coffee bean that you grind and brew to make a cup of coffee has changed quite a bit since it was harvested. The raw coffee beans, also known as green coffee beans, are dried, cleaned, and roasted to become the coffee beans used for drinking. Roasting is the process of heating green coffee beans to enhance their flavor and aroma, as well as improve their solubility in water. This process causes chemical reactions within the coffee bean. The science of coffee roasting results in a brown, aromatic, and flavorful coffee bean that can then be ground and brewed. 

roasting coffee beans

Why do coffee beans need to be roasted?

While you can technically make coffee from green coffee beans, it does not resemble what you would normally consider a traditional cup of coffee. Green coffee beans are much softer and spongier than roasted beans, and they lack the flavor and aroma associated with coffee. Roasting is necessary to bring out the flavor and aroma from coffee beans. 

What happens during the coffee roasting process?

Roasting uses heat to trigger chemical reactions within the coffee bean, followed by rapid cooling to stop the process and prevent over-roasting the beans. There are five main stages to the coffee roasting process. 

  1. Drying or Yellowing
  2. The Maillard Reaction
  3. The First Crack
  4. The Second Crack
  5. Carbonization

During the drying or yellowing stage, the chlorophyll in the coffee bean begins to break down. This causes the bean’s color to fade from green to yellow or gray. The heat is also causing the bean to start drying out. 

Next, the Maillard Reaction occurs. This is one of many chemical reactions occurring during the roasting process, but the Maillard reaction is one of the key reactions in developing the flavor of the coffee bean. During this phase, the amino acids and sugars within the coffee bean react, causing the beans to turn brown. Volatile compounds are formed, producing the aroma of coffee. Caramelization will also occur as the beans continue to get hotter, contributing to the color, sweetness, complexity, and flavor of the coffee. As the roast continues, the coffee beans will continue to darken. 

The first crack happens around 385° or 390°F (196°C or 199°C). This is when the pressure of the water vapor within the coffee bean causes the bean to expand, releasing water and oxygen. The beans become more porous and brittle, losing some of their density. The first crack sounds similar to popcorn kernels popping. 

The chemical reactions continue following the first crack, and this time will have the most influence on the final result from the roasting. Lighter roasted beans will display more of the characteristics of the bean, while darker roasts will be more characteristic of the roasting process. The extent of the roast will also impact the bitterness versus sweetness of the coffee, as sugars are broken down and others are formed.

The second crack occurs when the cellulose in the coffee bean weakens and begins to break apart, releasing carbon dioxide and oils. Instead of popcorn popping, the second crack sounds more like oil sizzling and crackling in a frying pan. At this point, the coffee beans will be a darker roast. 

If the coffee beans continue roasting, they will reach carbonization, or burning. The coffee bean begins to break down and burn, creating a fire hazard. 

Once the coffee beans have reached the desired roast, rapid cooling is used to stop the chemical reactions and prevent them from over-roasting. The primary methods of cooling are air or water quenching. Air quenching uses fans to cool the beans, while water quenching uses a spray of water, which quickly evaporates. 

While freshly roasted coffee shouldn’t be used immediately, as the flavor needs time to set up, the coffee beans should be used within three weeks of roasting for the freshest coffee. Coffee beans will begin to lose their flavor and aroma upon contact with air due to the evaporation of compounds. 

Learning More about Home Coffee Roasting

Are you interested in trying to roast your own coffee beans at home and experiencing the science of coffee roasting firsthand? Check out more of our home coffee roasting resources

Jars of roasted coffee beans