Coffee is deceptively complicated. At its simplest, coffee is only ground cherry seeds (the beans) and water.
However, these two ingredients give rise to a world of complexity when you consider how green coffee beans are roasted and ground and how you prepare the water for brewing.
This article explores the science of coffee in depth, from how the water you use affects your coffee’s taste to why grinding your own beans at home makes your coffee better.
Time to get ready for some coffee science! Grab your lab notebook and a hot cup of coffee.
Coffee chemistry 101
1. Roasting
Now that we are done discussing plants, lets move on to chemical reactions. The process of roasting coffee is rich and complex, with many nuances and subtleties. It takes experts years to perfect their craft of roasting, and their main struggle is with the chemistry involved.
The first challenge in coffee roasting is heating green coffee beans to the point where chemical reactions are started, without roasting them too much and causing pyrolysis.
When a material is heated above its decomposition temperature, it undergoes a chemical process called pyrolysis. In pyrolysis, the first step of combustion, substances are heated to extremely high temperatures in the absence of oxygen. Wood charring is one example of this process.
If you think that combustion and charring both sound bad for coffee beans, you are correct. Coffee roasters avoid exposing their coffee beans to full pyrolysis.
While one chemical reaction creates an unpleasant taste, another chemical reaction is what coffee roasters strive for. The Maillard reaction is a chemical reaction that occurs when food is heated and involves the interaction of sugars and amino acids.
The Maillard reaction is what gives browned food its unique flavor. This includes baked crusts, browned meat, and caramelized onions.
When roasting coffee beans, care must be taken when the temperature reaches 302°F as this marks the start of the Maillard reaction.
How long a batch of beans is cooked for affects its flavor. Shorter coffee bean roasting times result in beans that are sweeter and more acidic, while longer roasting times give the beans a maltier flavor.
2. Brewing
Chemistry is a key player in both coffee roasting and brewing.
In general, there are two main types of brewing methods: immersion brewers, where coffee grounds soak in water, and percolation methods, where water passes through ground coffee.
There are two brewing methods, immersion and percolation. They both work by mixing coffee grounds and water, but they do it in different ways.
It’s easy to think that the key to making coffee is simply giving the coffee grounds time to dissolve in the water. However, while dissolution is important, it’s not the most crucial element.
Coffee grounds dissolve once they come into contact with water; however, the process of moving flavor molecules from the inside of the coffee grounds to the edge takes more time.
The faster movement of particles at high temperatures results in more flavor being extracted from coffee grounds.
The coffee grounds in immersion style brewing methods are kept at a higher temperature than in percolation brewing methods.
We need to make the French press coffee grounds take longer in order to extract a similar amount of flavor from both a French press and a pour over.
Since flavor is more pronounced in a high-temperature French press, baristas grind the beans more coarsely, so the flavor has farther to travel from the center of the particles to the edge.
3. Morning Coffee Brewing Temperature
What will happen if we change the temperature when brewing coffee, but keep all other variables the same?
Temperature affects the solubility and rates of compound extraction. Although you can make a cup of coffee using ice water, it would not taste as strong as a cup made with boiling water. Additionally, it would take a very long time to brew a decent cup.
The process of making cold brewed coffee involves placing ground beans in cold water and allowing it to brew in the refrigerator for a prolonged period of time. This results in a lower rate of extraction, meaning that the final product will have a more subtle flavor.
The temperature of the water moderately affects how much caffeine can dissolve in it, and strongly affects how much organic acids can dissolve.
Coffee that is brewed overnight in a fridge should have low caffeine levels and be less bitter than coffee brewed with boiling water.
When you use boiling water, everything is extracted much faster, resulting in high levels of caffeine and bitter organic acids.
The temperature of the water used to brew coffee must be taken into account when considering the volatility of oils.
The rich flavor of coffee is due to the organic acids and caffeine evaporating along with the steam. This means that the perfect cup of morning coffee should not be brewed in extreme temperatures. The coffee will not taste as good if it is brewed in extreme heat or extreme cold.
4. Coffee Brewing Time
The best cup of coffee is one that has the most volatile oils and caffeine but limited amounts of bitter organic acids.
You can control the amount of coffee elements extracted by changing the brewing time.
This is the amount of time that the water is in contact with the ground beans, letting the oils, caffeine, and acids to dissolve.
If you don’t let the coffee steep long enough, you’ll end up with a cup that’s high in caffeine but low in taste, aroma, and richness.
If you extract coffee for too long, the levels of organic acids in your cup will be too high, making the coffee taste bitter.
It takes some trial and error to figure out how long it should take to brew a perfect cup of coffee. Other factors that affect the duration of extraction are the temperature and coarseness of coffee beans.
To make a perfect cup of coffee every time, you would have to experiment with the brewing duration for the same quality of coffee beans while keeping all other variables constant.
5. Water
The kind of water you use to brew your coffee is also an important factor. You might think that all water is the same, but different types of water can have different effects on your body. For example, tap water varies significantly from one location to another.
The mineral content in water alters coffee’s flavor by itself leaving a taste in your cup and also indirectly by changing how it is extracted.
There is a lot of debate among coffee experts about what mineral concentrations make the best coffee. Although there is no clear consensus, most experts agree that certain mineral concentrations produce the best results. Some companies offer mineral packets that can be added to distilled water to create the optimal mineral profile for brewing coffee.
6. Coffee-to-Water Ratio
The amount of coffee you use in relation to the amount of water is the most important part of making a good cup of coffee. If there is not enough coffee, your cup of coffee will taste weak, even if all the other variables are optimized.
When there is more coffee than water, the brew will be very strong. The amount of water you use when making coffee depends on the extraction method you use and other variables.
If you want to make a strong cup of coffee using a drip filter, you need to use less water than coffee because the temperature of the water is higher and the rate of extraction is also high.
If you are using a plunger or a French press, you will need to use more coffee beans for the same amount of water. This is because the temperature of the water decreases quickly.
You can control how much water is used in a shot of espresso, depending on your preferences. The water temperature is usually kept at 97 C.
7. Grind Size
When determining the grind size for coffee, one could argue that it is more of a physics topic than chemistry. However, since the grind size affects extraction, and extraction is a process full of chemistry, it makes more sense to keep it under the chemistry category.
We have talked about how big the pieces of coffee should be when using a French press compared to pour-over brewing, but we can go even smaller.
Freshly ground coffee beans release flavor-packed oils. When you grind coffee shortly before you brew it, those oils are still intact, which results in a more flavorful cup of coffee.
Coffee that has been freshly ground is more fresh than coffee that has been pre-ground. This is because freshly ground coffee hasn’t had as much time to be in contact with air. Coffee grounds start to oxidize when they are exposed to the air.
When coffee oxidizes, the chemical composition of the coffee changes and it is no longer good to drink. It isn’t dangerous, but it doesn’t taste very good. Processes like oxidation are not exactly appetizing.
How well the coffee beans are ground will also affect the taste of the coffee. Although the best and most expensive coffee grinders exist, they don’t always produce grind sizes that are uniform in size.
The ratio of large to small particles in the coffee beans will determine how the coffee tastes when it is brewed. The size of the particle dictates which flavor compounds are extracted, with smaller particles providing stronger flavors.
If your grinder produces too many small particles, it will be difficult to extract more subtle flavors from your coffee beans, and your coffee will usually taste harsh and bitter.
If you have a good coffee grinder, it will produce similar sizedGROUND COFFEE each time you use it. Having a consistent grind size will allow you to adjust other brewing factors to improve the flavor of your coffee.
If you’re looking for a consistently good cup of coffee, it’s worth it to invest in a good grinder. Cheap grinders and pre-ground coffee often have inconsistent grind size distributions, which can make it frustrating to get a good cup.
If you can only afford one coffee-making tool, make sure it is a high-quality grinder. A good grinder will have a dramatic impact on the quality of your coffee.
8. The Coarseness of the Bean Grind
The grind of the coffee beans and the duration of extraction are connected. If you want a strong coffee, you should use finely ground coffee beans. The larger the grind, the smaller the surface area.
This means that if you grind coffee beans into a fine powder, you will increase the surface area that is available for extraction. This will lead to a faster extraction of the desired compounds.
This can have positive or negative consequences depending on how long the extraction process takes. Turkish coffee is often fine-ground and boiled. This is what makes it very strong and bitter.
The tiny size of the coffee grounds results in a lot of suspended solids, which clog coffee filters and slow down the extraction process.
This results in a very quick extraction, but also a less complete one. Beans that are coarsely ground have a smaller surface area in contact with water, resulting in a quick extraction, but not a complete one. Although it would be time-consuming, it is possible to remove coffee beans from the ground coffee. However, doing this would be wasteful because the water would not be able to penetrate the beans.
If most of the elements are still inside the bean when it is thrown out, it is likely that it was not processed correctly.
The ideal grind size for coffee beans lies somewhere in between very fine powder and very coarse beans. The amount of time the hot water is in contact with the ground coffee beans affects the strength of the coffee.
The more finely ground your coffee beans are, the more caffeine, volatile oils, and organic compounds will be present in your cup of coffee.
If a cup of coffee tastes weak or bland, it means the beans were ground too coarsely or the water flowed through too quickly. If the coffee is extremely bitter, it means the grind was too fine and there are high levels of organic acids.
Conclusion
Did you enjoy our coffee science 101 crash course? Even though a lot of scientific advancements have been made in the coffee industry, there is still more research that needs to be done in order to improve the quality of coffee. Hopefully, the information provided in this article has given you a better understanding of the different aspects of the coffee industry.
A lot of coffee’s flavor comes from chemicals, so people who want to get the most out of their coffee beans need to know a lot about chemistry. That’s all for today; quiz tomorrow.